Slow strain rate tensile testing

The cracking susceptibility of a micro-alloyed HSLA-100 steel was examined and compared to that of a HY-100 steel in the as-received condition and after heat treatment to simulate the thermal history of a single pass weld. Slow strain rate tensile tests were conducted on samples of these alloys with these thermal histories in an inert environment and in an aqueous solution during continuous cathodic charging at different potentials with respect to a reference electrode. Both alloys exhibited reduced ductilities at cathodic potentials indicating susceptibility to hydrogen embrittlement. The results of these experiments will be presented and discussed in relation to the observed microstructures and fractography. 

Figure 4. Slow strain rate tensile test results at closed-loop controlled potentials with respect to a reference electrode (a) Reduction in area (RA) and (b) RA ratio (to H Free in Ni(g)).

Slow strain test. The strain rate chosen frequently for the tests, based on several studies, indicates important susceptibility to cracking at about 2 x 10 6 s 1 for steels, aluminum and magnesium alloys. However, the tests refer to open-circuit conditions and the strain rate sensitivity of cracking is dependent upon potential as well as solution composition. Where necessary the potential of the specimens can be controlled using a potentiostat during slow-strain-rate tensile testing.171 The reduction of area is a simple and appropriate way to quantify the susceptibility to SCC. 

Slow strain rate tensile testing Fracture Mechanics Testing... 

V.G. Silva, S.S.M. Tavares, I.P. Baptista, R. De Oliveira 2012. Evaluation of the susceptibility of a superduplex stainless steel welded joint to sulfide stress corrosion by slow strain rate tensile tests in sour solutions. Corrosion 68 (1), 015006. 

Edwards e/a/. carried out controlled potential, slow strain-rate tests on Zimaloy (a cobalt-chromium-molybdenum implant alloy) in Ringer s solution at 37°C and showed that hydrogen absorption may degrade the mechanical properties of the alloy. Potentials were controlled so that the tensile sample was either cathodic or anodic with respect to the metal s free corrosion potential. Hydrogen was generated on the sample surface when the specimen was cathodic, and dissolution of the sample was encouraged when the sample was anodic. The results of these controlled potential tests showed no susceptibility of this alloy to SCC at anodic potentials. 

The test method was initially developed as the Slow Strain Rate (SSR) smooth bar Tensile Test (SSRTT), but more recently, it has incorporated the use of notched and precracked or fracture mechanic types of specimens. The SSR is conducted in tension at a constant displacement rate in the strain range of 10 to 10 s and always produces fracture of the test specimen. The degree of susceptibility is measiured as a SSR-ratio in terms of the rupture properties, being more susceptible as the value of the SSR-ratio decreases from unity until it reaches a threshold (Fig. 23). 

Of the large number of SSC test methods that have been used to evaluate materitils for this service, five have survived uniaxial load tensile test. Shell bent beam test, C-ring test, double-cantilever-beam test, and slow strain rate test. The first four of these are incorporated in NACE Test Method for Laboratory Testing of Materials for Resistance to Sulfide Stress Cracking in HjS Environments (TM0177). Following are comments on these methods [3]. 

The following examples illustrate some particular characteristics of the SCC and CF phenomena which may be helpful in understanding the mechanisms involved. These examples often refer to slow strain rate tests, which are tensile tests performed in the EAC environment at very low strain rates (usually s ). The comparison of ten-... 

Figure 7 Aspects of the nucleation of SCC by localized corrosion, (a) Peak aged Al-Li-Cu-Mg alloy 8090 after unstressed preexposure in aerated 3.5% NaCl for 7 days, (b) SCC initiated from one of the fissures shown in (a), following removal of the solution and continued exposure to laboratory air under a short transverse tensile stress (courtesy of J. G Craig, unpublished data), (c) Creviced region of 316L stainless steel after a slow strain rate test in 0.6M NaCl + 0.03M Na2S203 at 80°C and an applied anodic current of 25 xA, showing unstable pitting leading to crevice corrosion and SCC initiation (courtesy of M. I. Suleiman).

One of the simplest and most useful tests performed on reflow-attached flip chips to determine the adequacy of the solder joints (i.e., C4) is a tensile pull test (Fig. 31). This is done by adhesively attaching a metal stud to the back of a joined chip and pulling the joints in tension at a slow strain rate (approximately 1.0x10 sec ). The pull force is measured during the test using an appropriate load cell. The pull strength is a useful parameter, but the failure mode is a very important indicator of joint quahty. Planar failure at the solder joint interfaces is indicative of a weak and unacceptable interface condition. 

Tensile tests are conducted at a constant strain rate. Static data are determined at a slow strain rate of 10 ((in./in.)/s). From the tensile data, a stress-strain curve is plotted as shown in Figure 2.1. From this curve, a number of important mechanical properties are determined. 

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