Stress rupture tests

Lead Although subject to slight penetration at 980°C it shows no detrimental effects in stress rupture tests when tested in molten lead at this temperature or at 815°C . It is highly resistant to mass transfer in liquid lead as indicated by data obtained in tests at 800°C with a thermal gradient of 300°C . ... 

Lead Tantalum is highly resistant to liquid lead at temperatures up to 1000°C with a rate of attack of less than 0.025 mm/y. It exhibits no detrimental effects when stress rupture tests are conducted in molten lead at 815°C . 

E. A. Sticha, Tubular Stress-Rupture Testing of Chromium-Molybdenum Steels with High-Pressure Hydrogen, Journal of Basic Engineering, December 1969, Volume 91, American Society of Mechanical Engineers, New York, pp. 590-592. 

Accelerated testing depends critically on selecting a parameter whose effect on service life is so well understood that long lifetimes at low values of the parameter can be predicted from shorter lifetimes at higher values. The parameter may be the prime cause of degradation, such as in a stress-rupture test where longer lifetimes at lower loads are predicted by extrapolation from short lifetimes at higher loads. It can also be a secondary parameter, such as when temperature is increased to accelerate chemical attack while the principal factor, chemical concentration, is kept constant. This is because there is more confidence in the relation between rate of reaction and temperature than in the relation of rate of reaction to concentration. It is clearly essential that extrapolation rules from the test conditions to those of service are known and have been verified, such that they can be used with confidence. 

Morscher and Sayir (1995) studied the effect of temperature on the bend radius that a c-axis-oriented sapphire fiber can withstand for fibers of various diameters. They did this by performing bend stress rupture tests on these fibers... 

C. A composition in this two-phase field should have superior high-temperature mechanical properties. Greskovich [21] has synthesized ceramics in this phase field, and high-temperature stress rupture tests showed that they are the most stable silicon nitride ceramics among all of the other systems studied. 

What this relationship, in effect, says is that every material will fail during creep when the strain in that material reaches a certain value independent of how slow or how fast that strain was reached. That the Monkman-Grant expression is valid for Si3N4 is shown in Fig. 12.14, where the range of data obtained for the vast majority of tensile stress rupture tests lies in the hatched area. On such a curve, Eq. (12.42) would appear as a straight line with a slope of 1, which appears to be the case. 

The mechanical behavior of these Be-rich phases and its variation with temperature has been studied by means of hardness tests, bending stress-rupture tests, tension tests and compression tests (Ryba, 1967 Marder and Stonehouse, 1988 Fleischer and Zabala, 1990 c Nieh and Wadsworth, 1990 Bruemmer etal., 1993). The observed brittle-to-ductile transition temperatures are of the order of 1000°C. The low-temperature fracture toughness has been found to be between 2 and 4 MN/m with practically no macroscopic ductility (Bruemmer et al., 1993), though there are indications of local plasticity at... 

Stress rupture tests on test pieces are very important under conditions where, in addition to the stress, the atmosphere is chosen to accelerate failure. The best known t> pe of test is a test of the so-called environmental. stress cracking of plastics, where the aggressis e atmosphere is a chemical that causes cracking when the material is in a strained state. These tests are usually considered as a form of chemical resistance test and are cosered in Chapter 14. Ozone cracking of rubber, also an environmental resi.stance test, is another example. 

Chiou and Bradley [81] conducted hydraulic burst and stress rupture tests on 1.28mm thick (58v/o 87/ 35/87° hoop filament wound) tubes made from E-glass fibre/Brunswick LRF-571 DGEBA epoxy resin. There were 6% voids in the laminate. A co-cured nitrile rubber liner was employed, partly to keep the inner surface dry and partly to ensure that pressure could still be maintained if the GRP cracked during the tests. The tests followed 6 months immersion in static simulated sea water (Aquarium Systems Instant Ocean, p = 1023 kgm, pH = 8.2). The tubes had a high (1.5%) moisture uptake, although some of this might have been free water in the voids, but saturation was not reached. 

The exposed tubes exhibited a 20% reduction in burst strength, compared to dry tubes. The acoustic emission response suggested that damage started in the wet tubes at a much lower pressure. Stress rupture tests, that is, pressurize and hold, were conducted at three pressures (four were claimed in the text, but only three levels were stated) with the highest pressure being close to the rupture pressure of the wet tubes. There was no indication of moisture-induced degradation, even for the worst-case scenario , that is simultaneous application of a constant stress and immersion... 

FIGURE 8. Tensile stress rupture testing in air of (0/90) Nicalon/BSAS composites Vf = 0.4... 

FIGURE 9. Results of constant stress ( static fatigue or stress rupture") testing for Nicalon/BSAS composite (a) Batch A and (b) Batch B tested at 1100°C in air. The solid lines represent the predictions based on the results... 

FIGURE 10. Fracture surface ofa 2-D Nicalon /Al203 composite following stress rupture testing at 1100°C in... 

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... 

The results of the stress rupture test at 1400°C are shown in Fig. 4. The threshold stress intensity factor below which no crack propagation occurs seems to be around 400 MPa as shown in Fig. 4. To understand slow crack growth in AI2O3 fibers and make accurate lifetime predictions, one needs to know the crack velocity as a function of stress intensity factor at high temperatures. It is well established that for a given... 

A considerable amount of mechanical properties design data on Alloy 800 has already been produced for SPX1, but certain additional work, especially long creep tests were necessary for confirmation. These long term creep/stress rupture tests include the effects of titanium and aluminium additions and welding evaluations. Work has been carried out mainly on pre-pressurised tubes tested at temperature 525 and 550 C. 

Creep and creep-rupture data may be presented as curves in different ways. One way is in terms of stress versus mpture time. Very often, instead of using the rupture time, the time until reaching a steady-state or minimum creep is preferred, because a much shorter period of time is required to collect creep-test data. Figure 6.100 is such a curve. Stress-rupture tests are used to determine the failure time, as mentioned above. The data are plotted as log—log curves. A straight line is... 

Long duration stress rupture testing was also done on this material. Five tests were carried out at various tempgratures. One at 700°C, three at 900°C and one at 1200°C. The lower temperature tests were done because Textron informed us that they have seen some degradation at these temperatures. There was no evidence of any unusual degradation at either of these lower temperatures. Three of the flexure bars, the one at 700°C and two at 900 0, survived for 500+ hours under a 250 MPa applied stress without failure, but with a small amount of permanent deformation. 

American Society for Testing and Materials, "Standard Practice for Conducting Creep, Creep-Rupture, and Stress-Rupture Tests of Metallic Materials," El 39-83, 1989Annuot Book of ASTM Sfondards, Vol. 03.01, p. 313. 

Thirty-two NT-154 tensile specimens were evaluated at temperatures from 1200 C to 1400 C. The first three specimens tested at 1400 C were to be loaded at 300 MPa for an exposure time of 100 hours. However, all three specimens failed during loading before reaching 300 MPa. As a result, an additional four tensile specimens were loaded to only 200 MPa for exposures at 1400"C up to 100 hours. At 1200 C five specimens were loaded to 300 MPa and four were loaded to 200 MPa for tensile stress rupture testing to 100 hours. The specimens that endured the 100-hour exposure were subsequently loaded to failure. In addition, five specimens were tested at 1250 C and six specimens were tested at 1300 C at 300 MPa. None of these tensile specimens survived the 100 hours. Five specimens were also loaded to 200 MPa at 1300 C for 100 hours. Fracture origins were determined by optical microscopy and SEM (JEOL/JSM-80 with EG G Ortec System 5000 Microanalysis System). 

The results of the tensile stress rupture tests for NT-154 at stress levels of 200 and 300 MPa are displayed in Figures 5 and 6, respectively. For an applied stress level of 300 MPa at 1250 C and 1300 C (Figure 6) the time-to-failure distribution was in two groupings approximately one order of magnitude apart. Similarly, at an applied stress level of 200 MPa at 1400 C and 1300 C (Figure 5)... 

Fifteen Hexoloy-SA specimens have been tested in tensile stress rupture at lAGOT. Applied stresses of 168.5, 200, 250, and 300 MPa were used. The results of the Hexoloy SA tensile stress rupture tests are summarized in Table 3 and plotted in Figure 9. 

Table 3. Summary of Tensile Stress Rupture Tests for Hexoloy SA...

Figure 3.1-126 shows some typical results of stress rupture tests characterising the time-dependent high temperature behavior dominated by creep deformation. A compilation of creep data may be found in [1.101]. 

It should be noted that creep- and stress-rupture-test data are obtained pnder atmospheric exposure additions in laboratories and under uniaxial loading. The stress condition existing in a vessel part under field service conditions Usually comprises stresses in three directions, a fact which complicates the application of the experimental data. In addition, the vessel material may be exposed to a corrosive atmosphere and be subject to scaling, hydrogen embritlle-menl, intergranular corrosion, and strain hardening. 

Voorhees, Sliepcevich, and Freeman (204) have presented a procedure for calculating the time of rupture from creep and stress-rupture data normally available to a designer. Prior to the work of Voorhees the design of thick-walled vessels at high pressures and elevated temperatures was usually based upon the maximum principal stress and an allowable stress determined from creep and stress-rupture test data. This is the current method recommended by the ASME code (11) for vessels operating at pressures up to 3000 psi. 

---