Effect of separation distance on cavitation erosion of vibratory and stationary specimens in a vibratory facility

Vibratory cavitation erosion with vibratory and stationary specimens is studied for three materials in tap water at room temperature. The separation distance is varied from 0.127 to 6.096 mm. Test materials were commercially pure lead, soft (1100-O) aluminum and type 316 stainless steel. The double-horn amplitude was 58.4 [mu]m (2.3 x 10-3 in) in a 20 kHz facility. The total duration of all tests was 10 min.The weight loss of both vibratory and stationary specimens of course depends on materials. The weight loss of stationary specimens is best correlated as a function of the reciprocal of the separation distance.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25720/1/0000277.pd

Comparison of cavitation erosion test results from venturi and vibratory facilities

A detailed comparison of cavitation erosion performance in tap water for five alloys in a vibratory (no-flow) system and a Venturi (flow) system was made. The effects of temperature variation (80 - 200 [deg]F), Venturi throat velocity (34 - 49 m s-1) and vibratory horn double amplitude were studied. Correlations between maximum erosion rate (maximum mean depth of penetration rate (MDPRmax)) and incubation period IP, and the material mechanical properties Brinell hardness and ultimate resilience UR = UTS2/2E. (where UTS is the ultimate tensile strength and E is the elastic modulus), were examined. Only moderate success was achieved in correlations between "erosion resistance" MDPRmax-1 and IP and these mechanical properties. However, a good correlation was found between MDPRmax and IP, pertinent to both facilities, of the form MDPRmax-1 = aIPn, where n is near unity (0.94). The cavitation intensity, as measured by MDPRmax, was found to be 10-20 times greater in the vibratory system, depending on horn amplitude and material. This ratio varies between 5 and 30 if individual materials are considered separately, being greatest for 1018 carbon steel and least for 316 stainless steel. This indicates the important differences in form between these cavitating regimes and the imprecision of material comparisons made in both regimes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24046/1/0000295.pd

Velocity exponent and cavitation number for Venturi cavitation erosion of 1100-O aluminum and 1018 carbon steel

The purpose of the present investigation is to evaluate the effect of Venturi throat velocity on the cavitation erosion of specimens for constant cavitation number, which is here based on Venturi discharge conditions. 1018 carbon steel and 1100-O aluminum were tested in the University of Michigan high speed cavitation tunnel with tap water at 27 [deg]C (80 [deg]F). Results of present tests are consistent with previous work done at the University of Michigan, showing that the velocity-damage exponent varies over the range +/-1-5 for the velocity range 10-49 m s-1.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23900/1/0000141.pd

Instrument system for monitoring cavitation noise

The aim of this work is to contribute toward the development of a monitoring system for cavitation damage prediction in hydraulic machinery particularly high performance centrifugal pumps. A high-frequency pressure-bar probe and digital acquisition and processing system have therefore been designed to measure the characteristics of damaging pressure pulses from cavitation in a venturi which simulates conditions in hydraulic machinery. Measurements were made of pressure pulse height spectra, which were used to develop a cavitation damage prediction method.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49107/2/jev15i7p741.pd

Cavitation erosion incubation period

To evaluate the "incubation period" (IP) stage of cavitation erosion, short-duration vibratory horn tests in tap water were made on soft aluminum alloy (aluminum alloy 1100-O) and also on a much more resistant alloy (316 stainless steel). Curves of weight loss versus time, and corresponding scanning electron microscopy photomicrographs taken during the IP, are presented and discussed. The effects of horn amplitude and temperature are investigated for "open-beaker" tests. The IP for 316 stainless steel is found to be about 500 times that for aluminum alloy 1100-O for the same amplitude and temperature. This ratio can be predicted almost exactly by applying an assumed relation between MDPRmax and IP, i.e. MDPRmax-1 = k(IP)n.Fatigue cracks and individual-blow craters were found for 316 stainless steel but only individual craters were found for aluminum alloy 1100-O, although their ductilities are approximately equal. It is found that the IP based on the eroded area only, IPerod, is much less than the conventional IP (based on the total specimen area) if IP is based on the attainment of a given mean depth of erosion MDP.Relations between the eventual erosion rate MDPRmax and the IP are considered. It is found that IP data can often be used to predict eventual MDPRmax values according to the relation MDPRmax-1 [is proportial to] (IP)n where n [approximate] 0.93 and n [approximate] 0.95 for our vibratory and Venturi data respectively. However, different values for n have been reported in the literature. By assuming a "characteristic" erosion-time curve the time of occurrence of MDPRmax can also be estimated.It is verified that only bubble collapse stresses are important in the vibratory horn test, although specimens are vibrated under very high accelerations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25242/1/0000684.pd

Cavitation damage prediction

New results from cavitating venturi water tests were used to reinforce the concept of cavitation erosion efficiency previously developed from tests in a vibratory facility with both water and sodium. The concept emerges from a technique which allows a priori prediction of eventual cavitation erosion rates in flow machines. Bubble collapse pulse height spectra obtained from submerged microprobes are correlated with measured erosion rates in given laboratory and/or field devices to allow this prediction. Preliminary results from such correlations are presented together with other measurements of the effects of gas content, velocity and cavitation condition upon the mechanical cavitation intensity as measured by the pulse height spectra.New results from vibratory facility tests in tap water and synthetic seawater upon three materials of variable corrodability (304 stainless steel, 1018 carbon steel and 1100-0 aluminum) are presented. The ratio between maximum erosion rates for the saltwater and freshwater tests were found to increase toward unity as the mechanical cavitation intensity is increased, i.e. increased mean depth to penetration (MDPR), as expected on theoretical grounds.The relation between the incubation period and MDPRmax was examined from the vibratory test results, and was found to depend upon the material properties as well as the fluid flow conditions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23641/1/0000605.pd

Vibratory cavitation erosion in aqueous solutions

Vibratory cavitation erosion tests on AISI-SAE 1018 carbon steel in tap water and in mild (0.1 M) aqueous solutions of CaCO3, CaO, NaHCO3 and NaOH were conducted at a temperature of 80 [deg]F (27 [deg]C), a double amplitude of 1.38 x 10-3 in (35.1 [mu]m) and a pressure of 1 atm. For the maximum (150 min) test duration the weight loss in tap water (no additive) is the smallest. However, this is not the case for shorter test times. The biggest difference between weight losses among the various solutions is about 10% - 30%, which is somewhat beyond natural data scatter for such vibratory tests. Released gases and also particles may play an important role in the results.There are three easily distinguishable damage regions for all cavitated surfaces, i.e. generally undamaged rim, central heavily damaged region and transition region, as for most vibratory tests. The relative areas of the three regions are about 53.5%, 0.13% and 46.4% respectively for the present tests.The erosion rate and extent of the damaged regions do not depend substantially on the solute tested. The very small area of the heavily damaged central region is presumably due to the relatively low horn amplitude used in these tests. The increase in damage rate with respect to tap water is about 50% for the maximum test duration.Surface photographs and scanning electron microscopy photomicrographs (for a test duration of 150 min) are presented. Cracks, intercrystalline fractures and single-blow craters are most concentrated in the central region, as would be expected.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25216/1/0000656.pd

Effect of temperature on the cavitation erosion of cast iron

Vibratory cavitation erosion tests of gray cast iron, together with tests of tool steel and 316 stainless steel for comparison, were performed at various water temperatures and horn amplitudes under a suppression pressure of 1 bar. The erosion processes for cast iron under the highest temperatures used (200 and 230 [deg]F, i.e. 93 and 110 [deg]C) are similar to those at room temperature. For each of the materials tested, the maximum weight loss rate increases, shows a peak and then decreases with increasing temperature. However, the maximum damage temperature for cast iron decreases with amplitude, i.e. 200, 170 and 160 [deg]F (93, 77 and 71 [deg]C) for double-horn amplitudes of 1.0 x 10-3, 1.38 x 10-3 and 1.78 x 10-3 in (25.4, 35.1 and 45.2 [mu]m). The peak for tool steel and 316 stainless steel occurs at 160 [deg]F (71 [deg]C) regardless of amplitude. Liquid temperature effects for cast iron erosion were explained by considering the interrelation between corrosive action and mechanical action due to cavitation bubble collapse.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25276/1/0000719.pd

Cavitation erosion of cast iron diesel engine liners

Photomicrographs from vibratory facility cavitation specimens and from an eroded liner of a field diesel engine are compared. The causes of erosion are similar. Corrosion tests show that the results are different from those from cavitation. This further confirms that liner erosion of a diesel engine is primarily due to cavitation erosion caused, in most cases, by vibration of the liner wall.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24050/1/0000300.pd

Effects of applied stress on cavitation erosion

Cavitation erosion under static applied stress and/or alternating stress was studied using steel specimens which were set in close proximity to an oscillating horn in ion-exchanged water. For increasing static applied tensile or compressive stress, weight loss and its rate do not vary in a monotonic fashion but first decrease, then increase through a peak, and then decrease again. Tensile stress except for given stress regimes, and compressive stress at all stress levels, decreases erosion damage compared with zero-stress values. Under alternating stress, the weight loss rate varies with trends similar to those under static applied stress. However, the weight loss rate is larger than for the same static stress, so that the erosion damage is more affected by alternating stress than by static stress. The behaviors under applied stress are discussed through the effect of stress on the erosion particles.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23926/1/0000171.pd