THE UNIVERSITY OF MICHIGAN College of Engineering Department of Mechanical Engineering Cavitation and Multiphase Flow Laboratory Report No. UMICH-324490-1-T LIQUID IMPINGEMENT AND CAVITATION STUDIES OF EROSION RESISTANCE OF RUBBER-COATED MATERIALS FOR B. F. GOODRICH by F. G. Hammitt N. R. Bhatt T. M. Mitchell N. Orlandea J. M. Stifel E. E. Timm V. M. Wild December 1970

ABSTRACT High-speed motion picture sequences of liquid jet impact at 500 MPH with 6 rubber-coated materials supplied by B. F. Goodrich and also with Epon-828 and Plexiglas have been obtained, showing in good detail the portion of the impact believed responsible for damage. Some conclusions on favorable characteristics of the splash pattern for superior damage resistance are made. The erosion resistance of the same materials has been measured with repeated impacts with the same water jet at 500 MPH and with a cavitation test. It was found that the erosion resistance measured with the water jet is quite similar to that measured on the Goodrich propellor arm at the same speed, and is also quite closely related to the cavitation resistance. Thus the water gun could be utilized for tests up to Mach 2 as has been done with materials such as Astrocoat for NADC. The best correlation with material mechanical properties or splash parameters was that with hardness. ii

TABLE OF CONTENTS ACKNOWLEDGEMENTS............................. iii LIST OF FIGURES.J..........................iv LIST OF TAB LES................................vii I. INTRODUCTION............................... 1 II. PHOTOGRAPHIC AND EXPERIMENTAL OBSERVATIONS.... 3 A. Experimental Facilities Utilized............... 3 1. Impact Facility...................... 3 2. High Speed Motion Picture Facility. 3 3. Cavitation Damage Facility.............. 4 B. Liquid Impact Photographic Results............ 4 III. EROSION OBSERVATIONS......................... 7 A. Impact Erosion Tests................... 7 B. Correlation of Impact Damage with Mechanical -and Collision Parameters................... 10 C. Cavitation Erosion Results.................. 10 IV. OVERALL COMPARISONS........................ 11 V. RECOMMENDED FUTURE WORK...................13 A. Prevention of Reduction of Cavitation Damage by Surface Flexibility...................... 13 B. Detailed Material Behavior in Liquid Impact to Initial Failure........................... 13 VI. CONCLUSIONS................................15 VII. BIBLIOGRAPHY....... 17 FIGURES......................................18 TABLES............, 0.... e e 0 73 VII. APPENDIX.. 77

LIST OF FIGURES Figure Page 1. Schematic of Water Gun Device........................... 18 2. High-Speed Motion Picture Sequence of Jet Impact - Goodrich #1............................................ 19 3. High-Speed Motion Picture Sequence of Jet Impact - Goodrich #3...................................... 20 4. High-Speed Motion Picture Sequence of Jet Impact - Goodrich #4............................................ 21 5. High-Speed Motion Picture Sequence of Jet Impact - Goodrich #5............................................ 22 6. High-Speed Motion Picture Sequence of Jet Impact - Goodrich #6.......................................... 23 7. High-Speed Motion Picture Sequence of Jet Impact - Goodrich #10........................................... 24 8. High-Speed Motion Picture Sequence of Jet Impact - Epon-828........................................ 25 9. High-Speed Motion Picture Sequence of Jet Impact - Plexiglas..................................... 26 10. Schematic of Cavitation Stationary Specimen, Vibratory Set-Up................................................. 27 11. Velocity Parameters During Liquid Jet Collision vs. Time from Initial Impact - Goodrich #1...............28 12. Velocity Parameters During Liquid Jet Collision vs. Time from Initial Impact - Goodrich #3 *.0 29 13. Velocity Parameters During Liquid Jet Collision vs. Time from Initial Impact - Goodrich #4.................... 30 14. Velocity Parameters During Liquid Jet Collision vs. Time from Initial Impact - Goodrich #5...... 31 15. Velocity Parameters During Liquid Jet Collision vs. Time from Initial Impact - Goodrich #6...............*.... 32 16. Velocity Parameters During Liquid Jet Collision vs. Time from Initial Impact - Goodrich #10..33

17. Velocity Parameters During Liquid Jet Collision vs. Time from Initial Impact - Epon-828................. 34 18. Velocity Parameters During Liquid Jet Collision vs. Time from Initial Impact - Plexiglas.................. 35 19. Water Gun Damage - Weight Loss (mg) vs. Number of Impacts - Goodrich #1................................ 36 20. Water Gun Damage - Weight Loss (mg) vs. Number of Impacts - Goodrich #3............................ 37 21. Water Gun Damage - Weight Loss (mg) vs. Number of Impacts - Goodrich #4................................. 38 22. Water Gun Damage - Weight Loss (mg) vs. Number of Impacts - Goodrich #5.............................. 39 23. Water Gun Damage - Weight Loss (mg) vs. Number of Impacts - Goodrich #6................................. 40 24. Water Gun Damage - Weight Loss (mg) vs. Number of Impacts - Goodrich #10........................... 41 25. Water Gun Damage - Weight Loss (mg) vs. Number of Impacts - Epon-828........................... 42 26. Water Gun Damage - Weight Loss (mg) vs. Number of Impacts - Plexiglas................................ 43 27. Water Gun Damage - Initial Period, Goodrich #3 and #10. 44 28. Water Gun Damage - Initial Period, All Goodrich Materials...............................................45 29. Goodrich Propellor Arm Weight Loss (500 MPH)............46 30. Damaged Specimen Photos, Impact to Left, Cavitation to Right - a) Goodrich #1, b) Goodrich #3 (x 1. 7).............47 31.. Damaged Specimen Photos, Impact to Left, Cavitation to Right - a) Goodrich #4, b) Goodrich #5 (x 1. 7).............48 32. Damaged Specimen Photos, Impact to Left, Cavitation to Right - a) Goodrich #6, b) Goodrich #10 (x 1. 7)............49 33. Damaged Specimen Photos, Impact to Left, Cavitation to Right - a) Epon-828, b) Plexiglas.......................50 34. Impact Data Correlation with Hardness.................... 51 35. Impact Data Correlation with Tensile Strength..... 52 36. Impact Data Correlations with Collision Axial Splash Velocity c*.....................................53 v

37. Impact Data Correlation with Collision Radial Splash Velocity......................................54 38. No. Impacts for 1 mm3 Volume Loss - Impact Tests vs. Incubation Period.................................... 55 3 39. No. Impacts for 3 mm Volume Loss - Impact Tests vs. Incubation Period...................................... 56 40. Cavitation Damage - Cumulative Weight Loss vs. Time - Goodrich #1................................... 57 41. Cavitation Damage - Cumulative Weight Loss vs. Time - Goodrich #3..................0.......*......... 58 42. Cavitation Damage - Cumulative Weight Loss vs. Time - Goodrich #4.................................... 59 43. Cavitation Damage - Cumulative Weight Loss vs. Time - Goodrich #5.................................... 60 44. Cavitation Damage - Cumulative Weight Loss vs. Time - Goodrich #6.................................. 61 45. Cavitation Damage - Cumulative Weight Loss vs. Time - Goodrich #10................................. 62 46. Cavitation Damage - Cumulative Weight Loss vs. Time - Epon-828...................................... 63 47. Cavitation Damage - Cumulative Weight Loss vs. Time - Plexiglas...................................... 64 48. Cavitation Damage - Comparison of Weight Loss Rates 65 49. Cavitation Data Correlation with Hardness............... 66 50. Cavitation Data Correlation with Tensile Strength......... 67 51. Correlation Between Test Devices - UM Water Gun 3 (1 mm3 volume loss) vs. Goodrich Propellor Arm (10 mm ). 68 52. Correlation Between Test Devices - UM Water Gun (1 mm3 volume loss) vs. Goodrich Propellor Arm (100 mm3)....... 69 53. Correlation Between Test Devices - UM Cavitation (1/MDPR) vs. Goodrich Propellor Arm (10 mm3)................... 70 54. Correlation Between Test Devices - UM Cavitation (1/MDPR) vs. Goodrich Propellor Arm (100 mm3)................... 71 55. Correlation Between UM Cavitation and UM Water Gun......72 vi

LIST OF TABLES Page 1. Materials Damage and Mechanic Properties................73 2. Liquid Impact Collision Parameters....................... 74 3. Comparison of Damage Between Test Facilities............. 75 vii

I. INTRO DUC TIO N An initial contract of one year between the B. F. Goodrich Co. and the Cavitation and Multiphase Flow Laboratory of the Mechanical Engineering Department of the University of Michigan had a three-fold objective: 1. Obtain high-speed motion pictures of the impacts of 500 MPH water jets generated by our water gun device upon 6 rubber-coated materials supplied by Goodrich to observe the details of this collision and attempt to ascertain possible differences in the response of materials that might be related to their droplet impact erosion resistance. The framing rates for these pictures should be such that as many frames as possible be available during the critical part of the impact process. The pictures were taken with our Beckman-Whitley framing camera capable of producing up to 80framesper run at 2 million frames per second. Due to the short time which can be sampled, optimum information in this case is obtained with less than maximum framing rate as will be explained later. Pictures have also been taken under the same impact conditions for two harder materials for comparison, Epon-828 and Plexiglas, 2. Investigate utility of this water gun device for the testing of rubber-coated materials for liquid droplet erosion resistance. Test data on the water gun device for the 6 materials supplied by Goodrich can be directly compared with results on the same materials at the same velocity generated by Goodrich using their propellor arm device. If a reliable relationship between results from these two devices could be shown at 500 MPH, data could then be obtained on the same or other materials of interest to Goodrich at velocities up to about 1200 MPH with the gun device (which has such a capability). A possibly significant difference between the two types of test at the moment is the fact 1

that the gun device impacts repeatedly in the same location on the specimen whereas the propellor arm provides a random distribution of impacts as does an actual rain storm. The capability of random distribution of impact could be added at moderate expense to the jet gun. 3. Investigate utility of our vibratory cavitation device for testing of the same materials for droplet impingement erosion resistance. Obviously, cavitation erosion data for these same materials are of interest per se, but their relation to impact data was to be investigated. All of the above tasks have been completed as will be explained in considerable detail in the body of the report. These preliminary results suggest the desirability of additional investigations covering at least another year of effort as will also be explained later. 2

II. PHOTOGRAPHIC AND EXPERIMENTAL OBSERVATIONS A. Experimental Facilities Utilized 1. Impact Facility. For the liquid jet impact tests, a repeating water gun (Fig. 1) was utilized. (1) This device produces liquid jets with velocity up to about 600 m/s, emanating from an orifice of 1. 61 mm.dia. The repetition rate is up to about 50 per minute. The actual jet shape depends upon various parameter settings. For the present tests, wherein the impact velocity was ~~223 m/s (500 MPH) its appearance is as shown in Fig. 2 - 9. The initial stage of the impact is with a "precursor jet" of diameter somewhat smaller than that of the main jet. Precursor jet diameter in these tests is' 1/3 mm. and main jet diameter is ^1. 2 mm. It is believed that the important part of the impact from the viewpoint of damage production is the initial part during which high transient pressures and velocities are possible. The pressure and velocity across the surface of a "steady-state'.' jet of the present impact velocity would be much smaller and probably not damaging during the short time of the collision. The six rubber-coated materials supplied by B. F. Goodrich Co. (Table 1) were tested at 500 MPH impact velocity, angle of impact perpendicular. Photographic sequences of the collisions were then obtained (Fig. 2 - 7) using the high-speed framing camera described in the next section. Collisions with two relatively non-elastic materi als (Epon-828 and Plexiglas) were also photographed (Fig. 8, 9) under the same conditions for purposes of comparison. Damage data (weight loss) were obtained for all these materials with repeated impact under the same conditions for which the photographs were made. (Table 1 and 3, and Fig. 19-28). 2. High Speed Motion Picture Facility. The motion picture sequences of the water jet impacts (Fig. 2 - 9) were made with a Beckman-Whitley framing camera capable of a maximum framing rate A modification to the device to provide a stripper plate allowing only the precursor portion of the jet to pass can be made in the future to obliviate this difficulty.

of 2 million frames / second, with a total of 80 offrames/run. To obtain maximum information per run, a framing rate of 0. 66 million frames per second was used. As will be observed in Fig 2 - 9, it is quite possible to estimate the radial and axial velocities of the liquid during the collision utilizing the times from initial impact noted on the individual photos. Note also that the flow patterns are well-developed by about 40 [s, and that there are considerable differences in flow patterns generated between the materials. These matters will be discussed in more detail later. Unfortunately it is not possible in these photos to observe the deflection of the specimen surface during the impact. However, from the steep angle of splash-back, it may be inferred that in some cas'es this deformation is considerable. A possible method for future tests for measuring the deformation during the impact and correlating it to photos such as these is discussed later in the report. 3. Cavitation Damage Facility. All the previously mentioned materials were also tested in cold water (70 F) in our vibratory stationary specimen set-up (Fig. 10) where the specimen is held 20 mils from the tip of the vibrating horn(). The double amplitude is 2 mils and the frequency 20 kHz. The resultant maximum damage rates are listed in Table 1 along with those fromthe impacttests. Generally it is noted that the correlationbetweenimpact resistance and cavitation resistance for these rubber-coatedmaterials is not good, especially when compared with the less elastic materials (Epon-828 and Plexiglas). B. Liquid Impact Photographic Results Fig. 2 - 9 respectively show high-speed motion picture sequences of impacts at 500 MPH (732 m/s = 233 m/s = 0. 67 Mach at STP) for the rubber-coated materials supplied by Goodrich and for the more rigid materials, Epon-828 and Plexiglas. Fig. 2 - 7 show the Goodrich materials in ascending rank according to the Goodrich numbers; Fig. 8 and 9 are for Epon and Plexiglas respectively. The times in microseconds

are shown in each frame. Though approximately 80 frames were exposed per run, only selected frames are shown to indicate the significant features of the impact. The portion of the overall impact shown by the figures is that with the "precursor" portion of the main jet which has a diameter of about 1/3 mm. The main jet of about 1. 2 mm diameter follows, but since this latter portion of the collision is a roughly steady-state impingement, as compared to the first portion, it is not thought to be important to the damage process. Though the impact phenomenon is quite similar for all the materials, there are significant differences in the velocity and direction of splash-back. This is minimal in the more rigid materials (Epon and Plexiglas), and quite pronounced in all of the rubber-coated materials, except for the natural rubber (Goodrich #1) which is similar in this respect to the rigid materials. It is maximal for Goodrich #4. Another difference which may be significant is the velocity with which the splash-back plume moves out radially from the center of the collision. This is maximal for Goodrich #4 and minimal for Goodrich #5 and 6 of the rubber-coated materials, but is considerably greater for the rigid materials. These trends are discussed in further detail below. Fig. 11 - 18 are plots of the velocity components taken from the photographs, Fig. 2 - 9. Some of the pertinent numbers from these plots are listed in Table 2. It is noted that typically both radial and axial splash-back velocity achieve a maximum very near the time of impact (0-1. 7.ts). In some cases both of these velocities are greater than the actual impact velocity, In all cases, the maximum radial velocity is greater than the actual impact velocity. In most cases, the maximum splash-back velocity is less.than the impact velocity, ranging from about 1/2 for Goodrich #4 to l. 3 x for Goodrich #5 and Epon-828. The initial radial velocity (which is also the maximum) is largest for Goodrich #3, being 2. 3 x the impact velocity for this material, and 2. 0 x When measured from actual point of impact, the radial splash appears to be quite symmetrical.

the impact velocity for Goodrich #10. It ranges from 1. 1 - 1. 3 x impact for the other materials. A large radial velocity may be significant in that Goodrich #3 and 10 were also most erosion resistant in the gun tests ('rables 1 and 3). It has previously been reported by other investigators, Brunton g')that radial velocities of 4 -5 x impact velocity are observed sometimes for impact of spherical drops upon materials such as Plexiglas (in our present tests the maximum radial velocity only slightly exceeded the impact velocity for this material). The reduced radial velocity in the present tests may be due to the fact that the jet nose is not perfectly spherical, and perhaps also to differences in impact velocity and drop diameter which would affect the surface deformation. The fact that the radial and axial velocities quickly decrease substantially tends to confirm the previously stated assumption that the significant damaging mechanisms exist only during the very early part of the collision, so that the remainder of the impact which occurs after the portion of the photographic sequences shown, is not important in this regard. Another significant difference between materials which can be observed in the photographs themselves, in the curve sheets, and in Table 2 is the degree of outward (radial) motion of the splash-back plume after the initial impact. For the rubber-coated materials this outward motion is minimal for the natural rubber, Goodrich #1, and maximal for Goodrich #4, 3 and 10 in that order. It thus appears that a large outward motion of the plume is desirable for erosion resistance (Table 1 and 3). Although the initial splash-back velocity is reasonably large for all materials tested, rubber-coated and otherwise, the photographs and Table 2 show that the actual height of plume attained is considerably the greatest for # 10, 4 and 3, so that this type of behavior is apparently desirable. Since the splash-back is presumably due to deformation of the surface under the impact guiding the velocity away from the surface, it is reasonable that it should be large for more flexible materials. Although 6

no actual observations of surface deformation during the impact were possible in these tests, a careful analysis of the photographs, with some assumptions, could allow its estimation. In further work, this might advantageously be done along with an attempt to measure the deformation, perhaps using ultrasonic or laser beam interference techniques. III. EROSION OBSERVATIONS A. Impact Erosion Tests The 6 rubber-coated Goodrich materials as well as Epon-828 and Plexiglas have been tested at the same velocity for which the impact photographs were taken (223 m/s). The weight and volume loss vs. number of impact curves are shown in Fig. 19 - 28, and the results are summarized in Tables 1 and 3. Prior to this initial set of tests, little knowledge of the behavior of materials of this type in the gun device and in this range of velocity existed. Consequently the tests were performed with the general objective of generating the full curve of weight loss vs. number of impacts until the coating had been eroded down to the substrate. Fig. 19 - 26 show such curves for the rubber-coated materials. Since the impacts occur repeatedly at very nearly the same spot when using the gun device, as opposed to the Goodrich propellor arm device where the impacts are random across the specimen surface as in an actual rain environment, a given degree of local attack upon the specimen corresponds to a much smaller total weight loss in the gun than in the propellor arm. Thus no direct comparison is possible at a given weight loss between the Goodrich propellor arm curve (Fig. 29), and the water gun curves for the same material. However, for a rough comparison, we have assumed that a given gun weight loss is equivalent in terms of local damage to either 10 or 100 x that weight loss for the propellor arm data. For the present however, the factor of 10 allows an extrapolation of the Goodrich data for 7

comparison with the gun data and will be used. If the factor of 10 were approximately correct, the gun tests correspond approximately to the propeller arm tests up to a weight loss of about 0. 2 gms (2. 0 gms for 100 x). The effect of both of these assumptions upon the relative ranking of materials by the propellor arm and gun devices is shown in Table 3, and will be discussed later. Once the general shape of the water'gun test curves for these various materials is known, it becomes apparent that time to initial failure rather than maximum weight loss rate (commonly used as the figure of merit for cavitation and impact tests on metals) is probably of primary importance. This could be characterized as the "incubation period", i. e., number of impacts to cause measurable weight loss. It could be measured by extrapolating to zero that portion of the weight loss vs. time curve which corresponds to an accelerated rate of weight loss. Examination of Fig. 19 - 26 shows that this is an uncertain procedure because of the substantial differences in detailed curve shapes. Nevertheless, incubation period as so estimated is listed in Table 1. Since there was no direct method for measuring the number of impacts to cause an initial failure of the coating (probably the most important figure of merit), an alternative approach has been adopted. The number of impacts necessary to cause a small but measurable weight loss is estimated directly from the weight loss vs. number of impacts curves. Table 1 lists the number of impacts necessary to cause 3 mm and 1 mm3 volume losses, as well as the "incubation periods" as defined above. Examination of Table 1 shows that the relative rankings of materials is much the same according to incubation period of impacts to either of the small volume losses used. However, the rankings according to maximum weight loss rate once gross failure has occurred (WLR of Table 1) are quite different. For example, according to any of the definitions of incubation period, Goodriod, Goodrich #10 is best and #3 next. According to maximum damage rate, #10 is still best, #6 is next and #3 is fifth. As will be discussed later, the cavitation resistance rankings of the materials according 8

to maximum damage rate is again somewhat different fromn the gun rankings with #4 being best, #3 the next, and #10 second from the worst. However, the rigid materials, Epon-828 and Plexiglas are far worsethan any of the rubber -coated materials. Examination of Table 3-c shows all Goodrich materials, with the exception of #4 and 10, hold the same ranking for cavitation and water gun. As indicated above, after initial tests had been completed on all materials, it became apparent that much greater detail in the early part of the test would be desirable, since the impacts to initial failure are probably much more important than the rate of failure once this occurs.' This suggests the desirability for future work of a more precise method for measuring initial failumresuch as might be provided with an ultrasonic probe, which conceivably could also measure deformation of the surface during the impact. This is discussed in more detail later. Though such an instrument was not available for the present tests, still a second run was made on the two materials appearing best in the first run, i. e. #10 and 3, with more numerous examinations and weighings. These results are shown in Fig. 27, where data from the initial portion of the tests for two specimens of both materials is shown. Average values for these materials are then used in Table 1. Fig. 27 indicates the considerable divergence between different specimens of the same material. Fig. 28 shows in more detail the results from the early portion of the tests for the other rubber-coated materials, so that comparison can be made. Fig. 29 is the Goodrich curve for the same materials from their propellor arm, also at 500 MPH. Fig. 30 - 33 are photographs of each material from both the water gun and the cavitation test after completion of the test. In all cases little or no damage can be seen in the photos from the cavitation tests, though slight damage could be seen in careful examination of the specimens. The damage from the gun tests is substantial and obvious. There is considerable difference in the damage pattern between materials. As previously mentioned more detailed probing of the very early portions of failure in future tests mightbe extremely rewarding. 9

B. Correlation of Impact Damage with Mechanical and Collision Parameters 3 Fig. 34 - 39 plot impacts to 1 mm volume loss (selected as the most meaningful figure of merit) against various parameters dependent upon the material properties, i. e., hardness, tensile strength, maximum radial velocity after impact, and maximum splash-back axial velocity. It is noted that the correlation is not particularly good with any of these, although those with either Shore-A hardness or microhardness seem best. Fig. 38 and 3 9 shows the correlations between "incubation period'" and impact to 3- 3 1 mm and 3 mm volume loss both of which are quite good since the impacts to "initial" failure seems of most basic importance, this parameter has been used for the remainder of this report. C. Cavitation Erosion Results Fig. 40 - 47 are plots of weight loss vs. time for the 6 Goodrich materials, Epon-828 and Plexiglas in the cavitation test. Since the rubber-coated materials are all very resistant to cavitation damage in this test as compared with more rigid materials (even metals), the weight losses in feasible test time are not sufficient to obtain closely reproducible cavitation damage curves. However, two specimens of each material were tested. Two separate curves for each specimen are shown on the curve-sheets, an averaged smoothed curve is then constructed, and finally a straight line from the origin to the average final weight loss. The slope of this straight line is then used as the figure of merit for the cavitation test for the particular material. Fig. 48 shows all these resultant straight lines without data points to allow an easy comparison between materials. The slopes of these weight loss lines are then converted into volume loss rates (MDPR) for Table 3. As shown on Fig. 48 and in Table 3, the rigid materials Epon-828 and Plexiglas are very much less resistant to this relatively mild cavitation field than are the rubber-coated materials. This was also true for the impact tests, but the differentiating factor was much less. 10

IV. OVERALL COMPARISONS Table 3 compares the erosion resistance data from the water gun and cavitation tests with that achieved with the same materials and velocity using the Goodrich propellor arm. In Table 3-A the actual numerical data from each type of test for each material is presented. This table including Astrocoat for comparison, which was tested with our water gun for NADC at a much higher velocity,( approximately 600 m/s). While the cavitation resistance of this material is not outstanding, its resistance to impact damage is very great compared to the Goodrich rubber-coated materials or the others tested (Epon-828 and Plexiglas), since no weight loss was obtained after 20, 000 impacts even at 600 m/s (vs. 223 m/s for the other materials). Table 3-B lists all the same results as Table 3-B as erosion resistances. These are normalized in such a way as to assign unity to Goodrich #1, i. e., all values are divided by the value applying in that particular test to Goodrich #1. Table 3-C gives the relative ranking of each material according to that particular test, with the most resistant material being assigned the highest numerical ranking. The rankings are presented with and without inclusion of Epon-828, Plexiglas, and Astrocoat which were not included in the Goodrich propellor arm test. Fig. 51-55 show the degree of correlation between the water-gun and the propellor arm; cavitation and the propellor arm; and water-gun and cavitation, respectively. The propellor arm data is shown both for time to 10 mm3 volume loss and time to 100 mm volume loss, as previously discussed. As shown in Table 3-C, the relative ranking of materials between the water gun and the propellor arm for 100 mm or for 60 minutes is nearly identical, the only difference being the interposition of materials #3 and #5 in the rankings. However, there is somewhat greater difference between the gun tests and the propellor arm time to 10 3 mm volume loss. This situation is also illustrated in Fig. 51 and 52. 11

Thus it appears that the damage intensity caused bythe water gun at 1 mm volume loss is similar to that for the propellor arm to 100 mm3 loss. As previously explained, the ratio between comparable volume losses is presumably the result of the fact that water gun impingement is closely upon the same spot, while that for the propellor arm is randomly distributed across the entire facial area of the specimen. Fig. 53, 54, and 55 show that for the rubber-coated materials there is a relatively good positive correlation between liquid impact and cavitation resistance with either the water gun or the propellor arm. As previously reported by this laboratory 1), this was not the case when comparing cavitation with the rocket sled (at Mach 2), or the gun (at Mach 2) with the rocket sled, although the gun and cavitation test correlated closely. Hence the correlation between water gun and cavitation is further confirmed by the present tests, although apparently neither device correlates well for elastomeric materials with the much more intensive erosion environment provided by the Mach 2 rocket sled. However, the correlation with ceramics or laminates was relatively good. The discrepancy for elastromerics could be partly due to aerodynamic heating of the specimens in the rocket test, to which elastomerics could be more sensitive. There are exceptions in the present test to the correlation discussed above between the water gun and cavitation test. Of particular note in this regard is Astrocoat which was extremely resistent to impingement damage but only mediocre with respect to cavitation. It is the somewhat intuitive belief of the first author that the relative ranking of materials will change considerably with the intensity of the erosion environment and that this is particularly the case for elastomerics. This is illustrated by the fact that there is good correlation between the cavitation test, water gun and Goodri ch propellor arm at 500 MPH, whereas the correlation between either cavitation or water gun (which correlated well together) and rocket sled at Mach 2 was inverse. 12

V. RECOMMENDED FUTURE WORK Obviously the work completed in this one-year contract is only a beginning in many areas, so that desirable and significant new work can be postulated in many areas. Two possible areas of major importance are suggested below. A. Prevention or Reduction of Cavitation Damage by Surface Flexibility It is theoretically expected and has been shown by past tests, (3) some of which were just recently completed inthis laboratory, that, while a rigid surface will attract a collapsing bubble and cause the orientation of the resultant microjet to be toward the surface, the inverse is the case with a sufficiently flexible surface, so that cavitation bubbles are actually repelled, and the microjet oriented away from the surface of the material. Thus a material with a suitably-designed flexible surface might be virtually immune to cavitation damage. Preliminary tests, (3) which we have completed with spark-induced bubbles collapsing adjacent to a rubber diaphragm stretched across an air space, -indicate that the theoretically postulated mode of collapse described above actually occurs. Hence, a further investigation of this phenomenon using our relatively unique high-speed photographic facilities with tests in both our venturi and beaker set-ups could point the way to the rational design of rubberized materials to take advantage of this facet of bubble dynamics. B. Detailed Material Behavior in Liquid Impact to Initial Failure A complete understanding of the actual material behavior under impact, and the mechanism for the initial failure, would be most desirable to aid in the more rational design of better materials. The presently completed tests show in detail the motion of the water during the significant portion of the impact from the viewpoint of damage. However, it is not possible to view the motion of the surface during this time. It may 13

be possible to infer this motion from the observed fluid motion, but this would involve a rather intricate and lengthy analysis which has not yet been done. The continuation of a computerized calculation of velocity and pressures on the surface of a rigid surface during impact to include the effect of surface deformation would allow the predication of these splash velocities and a check of the analysis against the present photographs. This essentially analytical approach should be continued, but further significant experimental information should be obtained as explained below. It may be possible to at least obtain a rough estimate of surface motion during impact by an ultrasonic probe. Initial investigation of this concept is fairly hopeful, so that a more detailed feasibility investigation should be pursued. Another possible approach is through the use of laser interferometry with a transparent surface. This appears feasible but would involve a fairly major effort. However, at least a preliminary evaluation of the concept would be worthwhile. Further use of ultrasonic techniques would be made for detection of initial flaws in the surface after a few impacts. The present tests, based only upon visual observation and measurement of weight loss, are not sensitive enough to detect the initiation of failure, and the form which it takes, Since it is believed that more detailed information on the actual failure mechanism would be highly desirable, it is recommended that an ultrasonic probe be employed in this regard. This probe could also at least provide some information on the deflection of the surface during impact. The precision of the latter data might be limited because of the difficulty of obtaining sufficient resolution of the ultrasonic beam. Such should not be the case with the laser beam technique mentioned above. 14

VI. CONCLUSIONS The major conclusions which can be drawn from this work follow. 1. It has been proven feasible to obtain detailed motion pictures of the impact from the water gun jet at 500 MPH upon 6 rubber-coated materials supplied by Goodrich as well as upon 2 relatively rigid materials,and this has in fact been done. The details of the resultant splashback, velocities and their directions, have been taken from these photos and listed in the report. The characteristics of the splash differ considerably between the rubber-coated materials, and between these and the more rigid materials. Comparing these photographic sequences with the measured erosion resistance of the materials to repeated impacts of the same form, it appears that a large radial and axial splash velocity, with the splash plume moving radially outward from the initial point of impact is desirable for superior erosion resistance. It appears that these velocity patterns would be the characteristics of a large surface deformation under impact, hence large effective surface elasticity, thus minimizing "water-hammer" pressures. The above remarks apply both to rubber-coated and more rigid materials (which in this case were less erosion resistant). 2. Results from both the water gun at 500 MPH and the cavitation device for the rubber-coated materials correlate quite closely with results from the Goodrich propellor arm (also at 500 MPH), if erosion resistance for the propellor arm is taken as the time to erode 100 mm from the surface. Erosion resistance for the water gun is then taken to be the number of impacts necessary to erode 1 mm from the surface, and the cavitation test erosion resistance is taken as the reciprocal of the maximum MDPR. The rational for comparing 100 mm3 volume loss for the propeller arm with 1 mm3 for the water gun is that the impacts are distributed randomly across the surface for the propellor arm but are concentrated at one point for the water gun. As previously reported(1) 15

the correlation is inverse between the Mach 2 rocket sled and the water gun at Mach 2) for this type of material. This indicates that the ranking of materials depends upon the intensity of the erosion environment. No detailed comparison of maximum volume loss rates in the impact tests has been made since this does not seem a good figure of merit. 3. For both impact tests,rated as described above, Goodrich #10 was uniformly the best material, Goodrich #4 was next for the water-gun, followed by Goodrich ff6 and #5. For the Goodrich propellor arm, the second best material is Goodrich #4, followed by Goodrich #3 and #5 In both cases Goodrich #1 (natural rubber) is worst, followed by Goodrich #4. Thus the correlation between results from the two devices is quite close. The cavitation results are somewhat similar, but #10 is.......... - worst for cavitation and #3 is best. Thus a good material for impact may not be good in cavitation. This is also illustrated by the behavior of Astrocoat. 4. Since the water gun and propellor arm results match reasonably closely at 500 MPH, the gun would be a useful device for extrapolating results for materials of interest to the 1500 MPH range of which it is capable. In this range, it was found in previous tests for Naval Air Development Center (NADC),that various materials were not eroded substantially a 20, 000 impacts (major damage with the present materials occurs 1000 impacts). However, Astrocoat, shown in Table 3, was better than the best of the present materials. 5. Correlations of damage resistance with characteristics of the splash and with material hardness and tensile strength have been made. It is found that the best correlation is with hardness. Brunswick Cross - Linked Polyethylene and Hughs on Elas tome ric, CD-1154-G4, e. g. See UMICH Report 02643-PR-5, December, 1970 F. G. Hammitt, et al. 16

ViI. BIBLIOGRAPHY 1. F.G. Hammitt, J. B. Huang, T.M. Mitchell, D. O. Rogers, E.E. Timm, "Cavitation and Droplet Irmpingement Damage of Aircraft Rain Erosion Materials", Proc. 3rd International Conference, Rain Erosion and Assoc. Phenomena, Farnborough England, 1970; also available as Report UMICH 02643-5-I, May 1970. 2. J'H. Brunton, "High Speed Liquid Impact", Phil. Trans., Roy. Soc., A, 1110, 260, July 1966, 78-85. 3. E.E. Timm, Unpublished Data, 1970. 17

ORIFICE PLATE DIAPHRAGM FEED WATER i BOLT SPRING 2765 Figure 1. Schematic of Water Gun Device

GOODRICH *1 T=O.OO s T= 1.67 ps T= 6.67 7s T= 15.00 ps T=23.33 s T=31.67 ps T=40.00 Es 3)02 Figure 2. High-Speed Motion Picture Sequence of Jet Impact - Goodrich #1

GOODRI CH #3 ~i ~~~~~~~~~~~~~~~~~~~~~ ~ ~~~~~~~~~~~~~~~~~~~ iiii:i::,:: TOOO ps T= 1.67 /s T=6.6 7 js T= 15.00 its T= 23.33 jas T=31.67 ~ T=40.00 jLs 3103 Figure~~~~~~~~~~~~~~~~~~~~~~~~~~~ 3. Hig Spe Motio P'icturte Seqec o;; i00f J!f e iV t! f Im p ac~~~~~~~~;t:: G o d r c #3 tt ~ f yft td0:;': f0i ft;t0000;:'t0 00;ii;;t0':000f000000000

GOODRICH #4 II T=O.OO,s T-I 1.67 /,s Ima' - Gr #4 Th6.67 ps5 Tb15.00 p5 T=23.33 s T=31.67 As T=40.00 p S 3104 Impact - Goodrich #4

GOODRICH #5 1: l: f:::::: S:: i:: 0: {::::::_0:::: f::+: 0 000::: T=O.00,s T= 1.67 ps T-=6.67 &s T8 15.00 /s ~~~jt,::: rT= 23.33 /Ls T-=3 1.67 p s::~~~~~~~~~~~~~~~~~~:: I e,,: /: T7 40.00 3 s 3105 Figure 5. High-Speed Motion Picture Sequence of Jet Impact - Goodrich #5

GOODRICH #6 ( T=O.OO ps T= 1.67 ps T=6.67 ps T= 15.00 Ps Mt T= 23.3 ps T= 351.67 s T= 40.00 s 3106 Figure 6 High-Speed Motion Picture Sequence of Jet Impact - Goodrich #6

GOODRICH #10 T=0.00 s T=1.67 1us T=6.67 ps T= 15.00 p s T=23.33 s T= 31.67 a T= 40.00 s 3107 Impact- Goodrich #10

EPON 828 LAMINATE >5 4 T=0.00 us T 1.67 us:: ~ ui~::::: t:::::::::::::::.:.'-': T= 6.67 us T15.00 us: + ---- -- -------- --- - ---::: - -- -- T: 23.33 us T 31.67 us T= 40.00 us 3109 Figure 8. High-Speed Motion Picture Sequence of Jet Impact - Epon-828

sBIT2xald - 4edurI 4af jo aouanbas a:n43fid uoI.oJN paadS-qt.-H 6 anl.1d Sd 0000tI=J 8~01~ 1si O Ob=L SV IXlc:: X s I 00-11 asW L900'9=1 si L9'1-1 SS 00V0'1.S. f:.~S~flX7

L ~OSCILJATOR OSCILLOSCOPE FREQUENCY COUNTER O ] TRANSDUCER ASSEMBLY ACCELEROMETER 150 WATT PIEZOELECTRIC POWER AMPLIFIER VESSEL TOP PLATE |k ~E EXPONENTIAL TEST FLUID~ 0 HORN -TEST TEMPERATURE 0 SPECIMEN CONTROL I' 0o 0 0 POW'ER SPECIMEN/ SUPPLY DISH CAVITATION VESSEL 2445 Figure 10. Schematic of Cavitation Stationary Specimen, Vibratory Set-Up

Radial Velocity Right Impact Velocity =223 M/S V Axial Velocity Right TJ Axial Velocity Left 300 0 Radius of Maximum Axial Velocity Right 0. Figure 11. Velocity Parameters During Liquid Jet Collision Q Radius of Maximum Axial Velocity Left vs. Time from Initial Impact Goodrich #1 200' >1~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~U U 0. 100 -0.: i 0O 0 5 10 15 20 25 Time (v s)

o Radial Velocity Left Impact Velocity a Radia-l Velocity Right 223 r/s ~ Axial Velocity Right V Axial Velocity Left 600 O Radius of Axial Velocity Ri'ght Radius of Axial Velocity Left Soo 500 300 Figure 1Z. Velocity ParameterS During Liquid jet Collision vs. Time from Initial Impact- Goodrich #3 200 100 0 5 10 15Is 20 25 30 35 40 Time (G s)

o Radial Velocity Left GOODRICH #4 A Radial Velocity RightImatVlcy =223 rn/s Axial Velocity Right 300 V Axial Velocity Left - El Radius of Axial Velocity Right 4Radius of Axial Velocity Left 200A2 0~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~0 > 100Figure- 13. Velocity Parameters During Liquid el olso vs. Time -from Initia 1 Impact -Goodich# 10 ~~15 20 25 30 35 404536 Time (p s)

O Radial Velocity Left GOODRICH #5 n Radial Velocity Right Impact Velocity + Axial Velocity Right = 223 r/s VJ Axial Velocity Left 300 3 O Radius of Axial Velocity Right KO Radius of Axial Velocity Left Figure 14. Velocity Parameters During Liquid Jet Colision vs. Time from Initial Impact - Goodrich #5 200 U o~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~w 100 0 1 ~ ~ 10 5 10 15 20 25 30 35 40 45 Time (hrs) 3165

'VJ Radial Velocity Left GOODRICH #6 A Radial Velocity Right Impact Velocity + Axial Velocity Right = 223 r/s 300 V Axial Velocity Left 300 E Radius of Axial Velocity Right O Radius of Axial Velocity Left 200 CD E -U vs. Time from Initial Impact Good 10 540 0 10 15 20 25 30 35 3166 Time (pLs)

O Radial Velocity Left GOODRICH # 1U L\ tRadial Velocity Right Impact Velocity ~ Axial Velocity Right = 223 m/s | V Axial Velocity Left E~ Radius of Max. Axial Velocity Right_ Radius of Max. Axial Velocity Left -3 500 2. 400 3 300 2001- ~ Figure 16..Velocity Parameters During Liquid Jet Collision 1 vs. Time from Initial Impact - Goodrich #10 100 ~0 5 ~ 10 15 20 25 30 35 40 45 50 Time (hrs) 3167

O Radial Velocity to Left (in photo) EPON 828 LAMINATE L\ Radial Velocity to Right (in photo) + Axial Velocity at Right (in photo) Impact Velocity = 223 m/s V Axial Velocity at Left (in photo) 300 Radius of Max. Axial Velocity Right 6 Radius of Max. Axial Velocity Left 7' 5 200 4 U L;I I, I I I I, 1.9-4 10 15 20 25 30 35 40 Figure 17. Velocity Parameters During Liquid Jet Collision vs. Time from Initial Impact - Epon-828 Time (hrs) 3168

rCt L4CLL t. -Radial VeloctyRgt Avia Iy R igh t Z)r 300 Ailt~ ~-~3 OctyLeft Impact Radius of A Velo3 m6 city XilVelocity,,gt -Radiu, Of Axial Vlc Ilcty Lteft 200 L I/ 0~~~~~~~ Pi loo ~~~~~~~~~- \\ - ~ ~ ~ ~ ~ ~ ~ ~ ~~~oct0,a -rarxiete~~~~~~~~~~~~I; rne s)

2O0 | GOODRICH #1 WLR = 0.039 mg/imp 19 Incubation Period - 10 imp Impact Velocity 18 = 223 m/s Jet Diam' 0. 33 mm 17 16 15 14 13 12 11 10 / 9 6 5 / 4 O 3 L- /Figure 19. Water Gun Damage - Weight Loss (mg) vs. Number of Impacts - Goodrich #1 So ]CT l l I 0 100 200 300 400 500 600 700 Number of Impacts 3170

GOO DRICH #3 WLR = 0.0595 mg/imp Impact Velocity Impact Velocity Incubation Period = 1000 imp = 223 m/s Jet Diam - 0. 33 mm 8 / ~/~0 / 3 /0 0o/ 4 Figure 20. Water Gun Damage - Weight Loss (mg) vs. 2 / Number of Impacts - Goodrich #3 0 I I I I I I I i'00 200 300 400 500 600 700 800 900 Number of Impacts 3171 3171

20 GOODRICH #4 WLR = 0. 0802 mg/imp 19 Incubation Period 380 imp Impact Velocity = 223 nu/s 18 Jet Diamond 0. 33 mm 17 16 / 15 14 13 12 11 10 9 8 7 6/ 5L/ 3 / 2 / Figure 21. Water Gun Damage - Weight Loss (mg) vs. 1 Number of Impacts - Goodrich #4 0 /I1 I I i 0 100 200 300 400 500 600 700 800 900 NUmber of Impacts 3172

i. 3 GOODRICH #5 WLR = 0.05 mg/imp Impact Velocity Incubation Period - 0 2 223 rn/s 1. 2 -- Jet Diam a- 0.33 mm 1. 1 1.0 0 O 0. 9 0. 8 0. 7 o.6 0.5 0 0.4 - / 0.3 0.2 2 Figure 22. Water Gun Damage - Weight Loss (mg) vs. fo~~~ l LllNumber of Impacts - Goodrich #5 0.1 o L,_. I I I I I. I i 0 o10 20 30 40 50 60 70 80 90 Number of Impacts 3173

20 r GOODRICH #6 WLR = 0. 0285 mg/imp Impact Velocity Incubation Period - 55 imp 19 1 = 223 m/s Jet Diarny 0.33 mm 18 17 16 15 14 13 12 / 11 10 9 8 7 6 5 4Figure 23. Water Gun Damage - Weight Loss (mg) vs. 2 r / Number of Impacts - Goodrich #6 V/ I i_ I _ - I I. 0 200 400 600 800 1000 1200 1400 Number of Impacts 3174

20 - GOODRICH #10 WLR = 0. 0129 mg/imp Incubation Period 4 730 imp Impact Velocity 18 = 223 m/s Jet Diam -0. 33 mm 17 16 O 15 14 O 13 12 11 10 / 9 0/ 7 1 O / 5 / 4 / Figure 24. Water Gun Danage -Weight. Loss (mg) vs. Number of Impacts - Goodrich #10 1 I... 1000 2000 3000 4000 5000 6000 7000 Number of Impacts

200 190 - Epon-828 WLR = 0. 125 mg/imp 180 Inc. Period = 880 imp 170 160 Figure 25. Water Gun Damage - Weight Loss (mg) vs. Number of Impacts - Epon-828 150 0 / 140 130 120 _ 110 100 O 90 80 70 60 50 40 30 20 10 0 400 800 1200 1600 2000 2400....2800 N umber of Impacts 3176

100 Plexiglas WLR = 0. 29 mg/imp Incubation Period = 1060 imp 90 Impact Velocity o = 223 m/s Jet Diam - 0. 33 mm 80 70 60 50 40 30 20 10 o Figure 26. Water Gun Damage - Weight Loss (mrg) vs. Number of Impacts - Plexiglas 0 4)0 800 1200 1600 2000 2400 2800 Number of Impacts 3177

Intial Period GOODRICH # 3 and # 10 Impact Velocity = 223 m/s Jet Diam -"0.33 mm 0 8/ 7 Spec. #1) x# 3 4 U GOODRICH- # 3 1..-> 2 fFigure 27. Water Gun Damage- Initial Period, Goodrich #3 and #10 0 I I I I I I I I I 0 250 500 750 1000 1250 1500 1700 2000 2250 2500 2750 3000 3250 3500 3750 4000 4250 4500 4750 5001 Number of Impacts 178

Initial Period All Specimens 10.0 Jet Diam" 0.33 Impact Velocity -223 rn/s / / ~#6 r~ 1 V Specimen0 Specimen 2 0 #4 J3 0~~~~~~~~ #3 Figure 28. Water Gun Damage - nitial Period,.2 ~~~~~~~~~~~~~~All Goodrich Materials.,~~~~~~~~~~~~~~ I:30 VD,o Number of Impacts 37

Comparative Weight Loss-Time Curves for 6 Elostomers Tested on the BFG Whirling Arm O-XA- 5435-1 -XA-5435-4 I (NATURAL RUBBER) (NEOPRENE) 0.9 0.8 Experimental Curv es - Guessed Curve -- 0.7 J | Sample: NACA 0025 Shape 6.5 in. Wide | Rain Rate: I in./Hr. Drop Size: 2mm t 0.6 - (Average Weighted by Volume) Impact Velocity: 500 mph E| Sample Radius 5 ft. (to Center of Sample) 0.5 I/ I 0O I -XA-5435-3 (NEOPRENE) 0.3 1 I / / XA-5435-5 0.2 1 // (NEOPRENE) I / / I -XA-5435-6 (NEOPRENE) 0. 1 0 -- 1 t _ XA-5435 —10. —.-G (ESTANE) 0 -I ~ 60 120 Testing Time (min.) — 3180 Figure 29. Goodrich Propellor Arm Weight Loss (500 MPH)

Ca) 3181 Figure 30. Damaged Specimen Photos, Impact to Left, Cavitation to Right - a) Goodrich #1, b) Goodrich #3

Cavitation to Right- a) Goodrich #4, b) Goodrich #5 b) Goodrich #5

ct0O ~ ~:'i ~:/~i.: i::~i~::!~,..i i.~.:i:;.:..'.':.:....~...~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~......... ~~~~~~~~~~~::.:..... (D o, I'i hJ i..~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~~~~~~~~~~~~~~~~~~ ~~ ~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~...... 00 c'P

-eltTtXIald (q "8 z 8 Fagd ( P - j3i2I oq u 0 he 4i,^ 9 ~4X@a 0,',j, pPaisir=4 5,.()s6iS4014 ursau dS pa~eBL ed ~E;a.Tnd 011 ~OB~AT - ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~s\ s f78T E~~~~p~

11 Epon-828 Impact Velocity 12 Plexiglas 223 M/s 1 Goodrich #1 Jet Diam - 0.33 mm 3 #3 4 " #4 5 #5 6 " #6 10 #10 O 10 0 3 11 O5 O 6 4 0 1 Figure 34. Impact Data Correlation with Hardness o10 20 30 40 50 60 70 80 90 100 Hardness (Shore A) 3185

1 Goodrich #1 2 Goodrich.#0 Impact Velocity I 223 m/s 3 Goodrich #3 Jet Dia - 0.33 mm 4 Goodrich #4 5 Goodrich #5 6 Goodrich #6 0o 2 0 3 100~ 06 0 4 Yigure 35,. ImIpact Data Corr~elation with Te.ns ile Strength 2400 2600 2800 3 3200 3400 (60 3800 4000 4200 Tensile Stength (psi) 3186

1 Goodrich #1 Impact Velocity 3 Goodrich #3 223 r/s Jet Diam 0.33 mm 4 Goodrich #4 5 Goodrich #5 6 Goodrich #6 10 Goodrich #10 11 GEpon 828 12 Plexiglas O 01 Spon 828 0 Figure 36. Impact Data Correlations with Collision Axial Splash Velocity! I...I I.I I I _ I I I I1 1 I. I!2'( 140 160 180 2P0, 220 240 260'280 300 Il' 14 l0? x al.V1qlty ynsec 3187

I Goodrich #1 Impact Velocity |- 3 Goodrich 43 = 223 m/s 3 Goodrich #3 - 4 Goodrich #4 Jet Dianm - 0.33 mm 4 Goodrich #4 5 Goodrich //5 - 6 Goodrich #6 10 Goodrich #10 11 Epon 828 12 Plexiglas 0 ) 0,, //'I'7 300; - 5. 100 4O 30 30 Figure 37. Impact Data Correlations with Collision Radial Splash Velocity.10 I I I I I I I I l I I _ 200 230 260 280 310 340 370 400 430 460 480 500 Radial Velocity m/sec 3188

1 Goodrich #1 Impact Velocity =223 m/s 3 Goodrich #3 4 Goodrich #4 Jet Diam 0. 33 mm Cl, 5 Goodrich #5 0 6 Goodrich #6 o 10 Goodrich #10 01 1000 11 Epon 828 S 12 Plexiglas 0 U )5 O10.0Figure 38. No. Impacts for 1 mm Volume Loss - Impact Tests vs. Incubation Period 10 I T U) JUiJ UUU Incubation Period (Impacts) 38

1 Goodrich #1 Impact Velocity 3 Goodrich #3 = 223 r/s 2,4 Goodrich #4 4j 4l Goodrich #4Jet Diam =0.33mm 10 o 5 Goodrich #5 4 6 Goodrich #6 10 *Goodrich #10 11 Epon-828 m 1000 12 Plexiglas S~~~~~~~~~~~~ 0 04 0 60, 100 ~ ~ 1 3 Figure 39. No. Impacts for 3 mm Volume Loss Impact Tests vs. Incubation Period 10 1I 11111 I I I 1111 I I I 11111 1 10 100 1000 10000 Incubation Period (impacts) 3190

Goodrich #1 WLR (average ) =0.026 MDPR (average) -0. 0695 0.r 0. Specimen a 0. 7 Average 0 O 0 0 / 0. Specimen b O00 0 0. / Stationary Specimen Vibratory Cavitation Test 700 F Water 0. 0 0 0.13 0 5 10 15 20 25 Time (hrs)

Goodrich #3 WLR (average) =.1 / MDPR (average) = 0. 0192/ Specimen b ~3-~~ Specimen a Stationary Specimen Vibratory Cavitation Test 20 kHz, 2 mil 700 F Water O Figure 41. Cavitation Damage - Cumulative Weight Loss vs. Time - Goodrich #3 O r __ I ~. i I I. I! 0 2 4 6 8 10 12 - 14 Time (hrs) 3192

Goodrich #4 WLR (average) = 80 MDPR (average) = 0. 158 8 r Figure 42. Cavitation Damage - Cumulative Weight Loss vs. Time - Goodrich #4 7 Specimen a 6 0/0 5 4Average 3 // / / / Stationary Specimen 2 / Vibratory Cavitation Test / / / 20 kHz, 2 mil 70 F Water A~~~~~/ B - [}Specimen b 0 1 2 3.4 5 6 7 Time (hrs) 3193

Goodrich #5 WLR (average) = 15 MDPR (average) = 0. 244 Specimen b 7 0 Average Stationary Specimen Vibratory Cavitation Test 20 kHz, 2 mil 70~F Wate r Figure 43. Cavitation Damage - Cumulative Weight Loss vs. Time - Goodrich #5 1 2 4 5 6 Time(hrs) 6 3194

Goodrich #6 WLR (average) =.44 MDPR (average) = 0. 075 ~2 / Average Specimen a.8 Stationary Specimen Vibratory Cavitation Test /.2 / / t~~~~~0 kHz, 2 rail 1..6 70 F0 Water Figure 44. Cavitation Damage - Cumulative Weight Loss vs. Time - Goodrich #6 0 ___ I.. _ I I I I _ O 1 2 3 Time (hrs)4 5 6 3195 7

18 - Goodrich #10 WLR (average) = 2.4 16 k MDPR (average) = 0. 517 14 Specimen b 12 10 Stationary Specimen Vibratory Cavitation Test 20 kHz, 2 miu 4 70 F Water i~ - 34 56 _/ Si ony Specimen a 3196 Time (hrs) Figure 45. Cavitation Damage - Cumulative Weight Loss vs. Time - Goodrich #10

EPON- 828 WLR (average) =27 MDPR (average) = 4.4 3i 25_ — S Specimen a 15 Stationary Specimen 0 / ~/ Vibratory Cavitation Test 20 kHz, 2 mil 700 F Water 10 - Figure 46. Cavitation Damage - Cumulative Weight Loss vs. Time - Epon-828 0 30 60 90 120 140 Time (min)

Plexiglas WLR (average) -52 MDPR (average) =11.4 Specimen a 16 15 14t Specimen b 13 Slope of Average Curve 12 11 / / - / Slope of Average Curve 10 7 Stationary Specimen Vibratory Cavitation Test 20 kHz, 2 mil / 700 F Water 5 4 3 Figure 47. Cavitation Damage - Cumulative Weight Loss vs. Time - Plexiglas a0'5 1 ~15 0 30 35 40 45 50 Time (minutes) 3198

10 Plexiglas Figure 48. Cavitation Damage - Comparison of Weight Loss Rate 8 r Epon-828 Astrocoat Goodrich #4 Goodrich #6 Goodrich #3 Goodrich #1 I ~~~~~1w~~ Time (hrs) 3199

1) Goodrich #1 11 3) Goodrich #3 4) Goodrich #4 5) Goodrich #5 6) Goodrich #6 12 10) Goodrich #10 11) Epon-828 12) Plexiglas 13) Astrocoat 0 13 0 10 05 01 /06 03 Figure 49. Cavitation Data Correlations with Hardness...I I I I I I i I I I 10 20 30 40 50 60 70 80 90 lOC Hardness (Shore A) 3200

1) Goodrich #1 3) Goodrich #3 4) Goodrich #4 5) Goodrich #5 6) Goodrich #6 10) Goodrich #10 1.0 Oio O5 _ O~6' ~ 0. 1 10 Figure 50. Cavitation Data Correlation with Tensile Strength ).01 __ 1 1 I I. I I 2400 2600 2800 3000 3200 3400 3600 3800 4000 4200 Tensile Strength (psi) 3201

1) Goodrich #1 3) Goodrich #3 4) Goodrich #4 5) Goodrich #5 6) Goodrich #6 10) Goodrich #10 0 10 000 -- 03 0 5 100 04 01 Figure 51. Correlation Between Test Devices - UM Water Gun (1 mm3 volume loss) vs. Goodrich Propellor Arm (10 mm3) 0 10 20 30 40 50 60 Goodrich Propellor Arm 10 mm vol. loss (min) 3202

1) Goodrich #1 3) Goodrich #3 4) Goodrich #4 5) Goodrich #5 6) Goodrich #6 10) Goodrich #10 > 120 min. 1000 03 Os 100_6 04 10 Figure 52. Correlation Between Test Devices - UM Water Gun (1 rmm3 volume loss) vs. Goodrich Propellor Arm (100 mm3) 10~ __ _- __ — 1 I I I! 0 20 40 60 80 100 120 140 Goodrich Propel]or Armn 100 nm3 vol. loss (min) 3203

1) Goodrich #1 3) Goodrich #3 4) Goodrich #4 5) Goodrich #5 6) Goodrich #6 10) Goodrich #10 LO O 03 06 10 / 10I Figure 53. Correlation Between Test Devices - UM Cavitation 1~. (1/MDPR) vs. Goodrich Propellor Arm (10 mm3 It 1.. I I I I 1 0 10 20 30 40 50 0 70 Goodrich Propellor Arm 10 mm vol. loss (min) 3204

1) Goodrich #1 3) Goodrich #3 4) Goodrich #4 5) Goodrich #5 6) Goodrich #6 10) Goodrich #10 LO00 0 3 06 10 05 Figure 54. Correlation Between Test Devices - UM Cavitation (1/MDPR) vs. Goodrich Propellor Arm (100 mm3) 1 1/ 1 _ 1 1 1 1 1 l 0 20 40 60 80 100 120 140 (nGoodrich Propellor Arm 100 mm vol. loss (min) 3205

3206 Figure 55. Correlation Between UM Cavitation and UM Water Gun 1) Goodrich #1 3) Goodrich #3 0 3 4) Goodrich #4 5) Goodrich #5 6) Goodrich #6 10) Goodrich #10 11) Epon- 8 28 12) Plexiglas 0 6 13) Astrocoat 04 4 010 0 12 0 11 10 100 1000 10000 No. Impacts for 1 mm3 vol. loss (impacts) 3206 72

Table 1, Materials Damage and Mechanical Properties Te nsile nu t MP Mate rial Hard nesss Strength~ Elo_~nangataion Density GCun WLR Cavit LR IM a t to -tIpcst e d v at Shore A psi %/ gm/cm3 mg/imp mg /hr. 3 rn o 1 m3n 3 V o 1lshr LosssLo Goodrich #1 36 4190 740 0. 97D 0 039 0. 026 81 1 09 Goodrich #3 62 2830 710 1.359 0 059 0. 15 ROO1001000.09 Goodrich #4 55 3090 580 1. 321. 0. 081 0. 80 300 2.5 Goodrich #5 37 2440 1000_ 1. ZZ9 0. 05 1. 10 630 1300 4 Goodrich #6 45 -48. Z730 1080 1. 574 o. oz9 0. 44 Z18 8 50 7 Goodrich #10 75-80 3000 900 1. Z15 0. 012 2. 4 Z490 17 200 1 Epon-8Z8 99.5 - 1. 60 0.125 52. 00 860 0 9 1 Lamnina te Plexiglas 99.5 - 1. 19 o. 29 Z7. 00 810 6 5 4 Astrocoat 89 1. —i.10.0-004 3. ZO 131 500 z 0 2 6 7

Table 2 Liquid Impact Collision Parameters Max. V Max. V Max. Radial Vel. Max. Plume Ht. Specimen of Splash-Back Plume (40 At s) m/s Mmm (Impact Vel. = 223 m/s) Left Right Avg. Goodrich #1 180 299 28 1.8 2.2 2.0 (0-1. 7 U,1s) Goodrich #3 299 539 108 3.3 3.7 3.5 (0-1. 7/A s) (0-1. 7 Ass) Goodrich #4 120 240 110 3. 8 5. 4 4. 6 (0 -1. 7/4k s) (0-1. 7/ s) Goodrich #5 240 299 37 2.8 2.7 2.7 (0-1. 7 /s) (0-1. 7/s) Goodrich #6 180 299 63 4.1 4.5 4.3 (0-1. 7/,s) (o-1. 7lAs) Goodrich #10 180 1170 80 4. 6 4. 5 4. 6 (0-1. 7pxs) Epon-828 240 299 170 2.0 2.2 2.1 (0-1.7 ks) (0-1.7/ s) Plexiglas 180 240 180 1.8 2.3 2.1 (0-1. 7/As) (o -1. 7 Us7s) 74

Table 3-A Comparison of Various Test Facilities Goodrich U-M U-M Material Propeller Arm Water Gun Cavitation Time for Time for Impacts for 1 3 ( DPR 3) hr/mil. 100 mm3 10 mm 1 mmDPR max Vol. Loss Vol. Loss Vol. Loss Min. Min. Goodrich #1 20 5 61 1.44 Goodrich #3 47 13 1000 52. 0 Goodrich #4 45 23 71 6. 32 Goodrich #5 75 7 143 4.10 Goodrich #6 95 15 86 13. 33 Goodrich #10 > 120 40 1370 1. 93 Epon-828 600 0. 088 Plexiglas 460 0.227 Astrocoat 12, 900 1.34 Table 3- B Erosion Resistance Normalized to Goodrich #1 Goodrich U-M U-M Material Propeller Arm Water Gun Cavitation Goodrich #1 1. 000 1. 000 1.000 1. 000 Goodrich #3 2.37 2.6 16.4 36.1 Goodrich #4 2.25 4.6 1.17 4. 38 Goodrich #5 3.25 1. 4 2.36 2.85 Goodrich #6 4.75 3.0 1.41 9.25 Goodrich #10 8.0 22.4 1.34 Epon-828 9.85 0.061 Plexiglas 7.58 0.15 72 Astrocoat 211. 4 0. 77 75

Table 3-C Relative Rankings for Erosion Resistance*' Goodrich U-M U-M Material Propellor Arm Water Gun Cavitation 3 3 3 10 mm 100 mm 60 min. Impacts to 1 mm Mils/hr. Goodrich #1 1 1 1 1 1 5 8 * Goodrich #5 2 4 4 4 4 2 5 Goodrich #3 3 3 3 5 7 6 9 Goodrich #6 4 5 5 3 3 4 7 Goodrich #4 5 2 2 2 2 3 6 Goodrich #10 6 6 6 6 8 1 4 Epon-828 6 1 Plexiglas 5 2 Astrocoat 9 3 *:Highest Value = Greatest resistance'-"-This column includes Epon-828, Plexiglas, and Astrocoat in the rankings 76

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