Stress durability test

W. J. Russell, R. Rosty, K. M. Adelson, M. J. Bodnar, R. F. Wegman, E. A. Gamis, and D. W. Levi, Use of Stressed Durability Testing to Evaluate Polyhydric Alcohol-Phosphoric Acid Pretreatment of Steel for Adhesive Bonding, Technical Report ARSCD-TR-83014, U.S. Army Research and Development Center, Dover, New Jersey (October 1983). 

Several other tests are used to correlate properties with the working conditions. The dynamic mechanical analyzer (DMA) is used to measure modulus and viscoelastic properties related to ductility. By using the DMA test method, the degradation in modulus could be imderstood and applied to the end use application. The effect of the environmental conditions is also tested the esthetic durability in heated environments is not restricted to warp and relaxation attributed to creep. Creep and stress relaxation tests are also done on SMC/BMC for their structural applications. The retention of color is critical for a heated appliance application. BMC/SMC can be formulated to offer excellent color stability when exposed to high temperatures. 

The method used for testing durability of adhesive bonds was developed at 3M by W.D. Sell (16) and is called "sustained load stress durability". The metal substrates were 2024T-3 clad or bare aluminum alloy, 5052T-4 bare aluminum alloy or 1010 cold rolled steel. The surface preparation for the aluminum alloys was either the "optimized" FPL-etch" or the H PO -anodization process (12). The steel was solvent wiped. If a primer was used, it was cured before application of the adhesive. Film... 

The sustained load that is applied to the bond in relation to the bonds control strength is certainly a critical parameter. Whether or not the load has any effect on the adhesive itself (analogous to stress corrosion cracking of metals) cannot be ascertained from our data. The literature, especially that of Bascom (19) would indicate that it does. This work does indicate that designers of adhesively bonded structure should take durability testing of this sort into account in their design exper imentation. 

Figure 10.5 shows the data obtained on an epoxy-nitrile film adhesive on 5052-H34 aluminum alloy after immersion in hot water for 50, 100, 300, 500, and 1000 hours. This test is very useful because it permits a large number of adhesive-bonded specimens with different adhesives, adher-ends, and surface pretreatments to be tested at the same time with a relatively small investment in man hours and equipment. Figure 10.6 shows a comparison of the stressed-durability data and unstressed hot-water-soak data on the same epoxy-nitrile film adhesive, using 2024-T3 aluminum alloy. Note the parallelism of the plots. The curve in the lower left was obtained when lap-shear specimens were subjected to various levels of stress and then exposed to an environment of 60°C and 95% RH until failure. The failure time is plotted as a log function. The curve in the upper right portion is a plot of the data when the same types of lap-shear specimens were subjected to 60°C water for specified periods of time and then tested for their residual strength. In the first case, failure time was recorded. In the latter case, residual strength was determined. The same type of data is obtained with both curves. ... 

Significant scatter is often evident in time to failure data obtained from stress rupture tests conducted on either neat materials or on bonded joints. This scatter may obscure trends and frustrate the user. Results are typically plotted as load level versus the time to failure, a form that is analogous to S-N plots used in fatigue tests (see Durability Fatigue). In keeping with the principles of polymer physics, the time to failure axis should be plotted on a log scale, as illustrated in Fig. 1. Many creep-rupture models for homogeneous materials are based on forms like... 

Cyclic tensile testing was done after exposure durability testing [16]. The as-received and an exposed curve (similar time and stress of exposed fiber push out sanqile) are shown in Figure 10. As can be seen from the cyclic tensile tests performed at room temperature both as received and post exposed that the exposed sample has a smaller hysteresis consistent with scenario 2 above. 

The cyclic immersion test and the stressed high-humidity (sustained load durability) test are particularly aggressive and are both discriminating tests for adhesive durability performance. 

Pt Distribution Changes in Catalyst Layer in Fuel Cell Performance Pt dissolution, redeposition, and agglomeration eause Pt to be redistributed in the catalyst layer. The redistribution of Pt coneentration and particle size in the cathode catalyst layer has been observed using TEM after both the durability test and the highly aeeelerated stress test. Figures 23.24 and 23.25 show the redistribution of partiele size and eoncentration of Pt in the cathode eatalyst layer. 

In this chapter, we discuss the morphology and surface chemistry that result from various preparations and the performance of the resultant adherend in bond strength and durability tests (i.e., performance in hot, moist environments while under stress). The emphasis is placed on those adherends and preparations for which there is a direct correlation between the surface morphology and chemistry and bond performance. (See also Chapter 9 by Minford.)... 

An objective comparison of the abrasion resistance of superhydrophobic surfaces has been hampered by the lack of a single, standardized test method. Likewise, no single measure has been used for characterizing the effect of wear. Moreover, all these different approaches induce very diverse surface topography modifications but at the same time all of them are referred as mechanical durability tests. This is very confusing for someone who wants to evaluate how durable is one surface compared to the other. Generally, abrasion resistance is most directly and commonly measured using linear shear abrasion. In this form, shear stress arises from the force vector component parallel to the cross section of the material. The most common approach, based on the number of published papers, for the evaluation of the mechanical durability of liquid repellent surfaces is... 

The Nffd) dependence is typically a linear decaying function when plotted on a log-linear scale, that is, log Nf = a - bo. As one can see, this expression is similar to the one established in the static durability testing. This similarity has a particular physical meaning (in a statistical aspect). Furthermore, the extrapolation to a 0 is not valid here either upon the lowering of the applied stress or strain to a particular value, the value of increases rapidly, that is, there is a cyclic fatigue limit similar to the static fatigue limit. 

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