Slow-strain-rate tension tests

FIG. 8—HT/HP test vessel for slow strain rate tension testing. 

ASTM G 129 Slow-Strain-Rate Tension Tests... 

Zirconium and its alloys are susceptible to stress corrosion cracking (SCC) in such environments as Fe - or Cu -containing chloride solution, CH3OH -H hahdes, concentrated HNO3, halogen vapors, and liquid mercury or cesium [4,5]. Common test methods, e.g., U-bend, C-ring, split ring, direct tension, double cantilever, and slow strain rate tension, have been used to determine zirconium s susceptibility to SCC. 

The equipment required for slow strain-rate testing is simply a device that permits a selection of deflection rates whilst being powerful enough to cope with the loads generated. Plain or precracked specimens in tension may be used but if the cross-section of these needs to be large or the loads high for any reason, cantilever bend specimens with the beam deflected at appropriate rates may be used. It is important to appreciate that the same deflection rate does not produce the same response in all systems and that the rate has to be chosen in relation to the particular system studied (see Section 8.1). 

For comparison, the following relationship has been found for an X70 pipeline steel (slow strain rate test using compact tension specimens with the precrack located in the heat-affected zone of a weld) ... 

Tests using a constant stress (constant load) normally by direct tension have been described in ISO 6252. This test takes the specimen to failure, or a minimum time without failure, and frequently has a flaw (drilled hole or notch) to act as a stress concentrator to target the area of failure. This type of testing, as well as the constant strain techniques, requires careful control of specimen preparation and test conditions to achieve consistent results (246,247). Use of a slow strain rate with a four-point bend specimen configuration and constant load has been suggested as a method for ranking materials for environmental stress-crack resistance (248). 

Stress-corrosion cracking (SCC) occurs on certain materials when exposed in select corrosive environments. Standards applicable for measuring the tendency of a material to tmdergo SCC involve immersion testing of stressed specimens and tension and slow strain rate testing. The following standards are applicable for evaluating a material s tendency for SCC in a select environment ... 

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). 

SCC susceptibility is more readily detected using slow strain rate techniques than normal tension testing. This is because the slow straining procedure allows the corrosion effects to occur [17]. Table 8 provides information on standard test methods for evaluating SCC. 

Slow strain-rate tests, in which standard tension test specimens are subjected to a constant extension rate of 10-4 to 10-6 m/s while being exposed to a corrosive environment, provide a relatively quick method for SGG screening of metals. Such methods are described in the following standards ... 

Category 3 tests use smooth or notched tension specimens that are dynamically loaded at very low strain rates the slow strain rate test (SSRT) is the primary example. 

Kivisakk [195] used SSRT to study the SCC of carbon and stainless steels in white hquor. Specimens were prepared to ISO Standard 7539-4, Corrosion of Metals and Alloys—Stress Corrosion Testing—Part 4 Preparation and Use of Loaded Tension Specimens. The SSRT was done in accordance with ISO Standard 7539-7, Corrosion of Metals and Alloys—Stress Corrosion Testing—Part 7 Slow Strain Rate Testing. 

Slow strain rate technique The specimen is pulled in uniaxial tension at a controlled very slow strain rate in a given test environment to detect its susceptibility to see. 

An experimental technique for evaluating susceptibility to stress-corrosion cracking. It involves pulling the specimen to failure in uniaxial tension at a controlled slow strain rate while the specimen is in the test enviromnent and examining the specimen for evidence of stress-corrosion cracking. 

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. 

Slow strain rate tests can be used to test a wide variety of product ftxms, including parts joined by welding. Tests can be conducted in tension, in bend-... 

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