Cracking, thermal history

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. 

The characterization of amorphous semiconductors is further compU-cated by the fact that the same chemical composition can exist in many structural states which depend on the thermal history and preparational variables. Moreover, compositional heterogeneity, voids, cracks, as well as the preservation in some materials of molecular structures with relatively extended short-range order makes real amorphous materials quite different from the ideal disordered systems presently studied by theorists. 

Special calculations related with the thermal history of the Moon show that soon after formation its subsoil was warmed up by radioactive heat and considerably melted, which was accompanied by intense volcanic phenomena to form craters and cracks. Besides, at early stages, a very large number of meteorites and asteroids dropped onto the surface of the Moon, at whose explosions craters of different sizes and stractures appeared as well. Now, meteorites drop onto the Moon much less often, and the volcanism degree has considerably decreased. 

Oil accumulations can continue to undergo thermal evolution, depending on the depth of the reservoir and subsequent geothermal history. As noted in Section 4.5.2, oil becomes susceptible to thermal cracking at temperatures above 160-200 °C. For example, paraffinic-naphthenic oils (Fig. 4.22) are degraded to aromatic-naphthenic oils (with moderate S content, <1%), and aromatic-intermediate oils degrade to aromatic-asphaltic oils (with high S content, >1%). 

As discussed by Rossmanith (1997), applications of cracks in materials can be traced to the late Shang dynasty (<1000 BC), where the will of the ancestors was made known through cracks produced by heating specially prepared bones or shells (note that the bulk of this section is based on the detailed history by Rossmanith, 1997). Applying a heated bronze rod to the bone would induce large localized thermal stresses which could produce a crack on the back side of the bone. The shapes of these cracks were interpreted by priests and the knowledge so derived was used to form an... 

The model Is based on elastic-plastic fracture mechanics principles, and Incorporates effects associated with thermal expansion mismatch and modulus mismatch of various constituents, as well as non-linear material behavior as a function of load and temperature. Key properties of the constituents, such as those of the interlayer, reaction zone, and base material are provided as a data base these data were measured in this program by using bulk samples, The model then uses the processing history, specimen geometry and loading conditions to evaluate the performance of the joint, The results of finite element analysis of cracked specimens have been consolidated In arriving at the engineering model, JADM,... 

Cause A metallurgical history of the pipe showed that it was exposed to tensile stresses, thermal stresses and residual stresses from weldment. The temperature reached about 45°C. Surface topography suggested intergranular cracking. 

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