Grain and phase stress criteria for behaviour and cleavage in duplex and bainitic steels

Stress analyses by X-ray diffraction are performed on a cast duplex (32% ferrite) stainless steel elbow and a bainitic (95% ferrite) pressure vessel steel. During an in situ tensile test, micrographic observations are made (visible glides and microcracks) and related to the stress state determined in the individual ferritic grains (aged duplex) and the ferritic phase (bainite loaded at low temperatures). Several material parameters have been identified at different scales, as for example, the critical resolved shear stress of 245 MPa for the aged ferritic grain (duplex) or 275 MPa for bainite (–60 ◦C), a crystallographic cleavage propagation criterion of 465 MPa (stress normal to {100} planes), and a fracture stress of approximately 700 MPa in the ferritic phase. Even though the two steels are different in many respects, the macroscopic fracture strains and stresses are well predicted by the polycrystalline model developed for bainite, whatever the temperatures tested (considering 7% of the grains reaching the local criterion)

“I Know This is Supposed to be More Like the Real World, But . . .”: Student Perceptions of a PBL Implementation in an Undergraduate Materials Science Course

This qualitative case study examines the initial implementation of a problem-based versionof an undergraduate course in materials science for the purpose of identifying areasof improvement to the curriculum prior to a planned second implementation. The coursewas designed around problems that students work in small teams to solve under the guidanceof facilitators, with early sequence problems designed to foster the problem-solvingskills required to succeed in the course. This report describes students’ impressions ofand experiences in the course as they worked to solve the final problem at the end of thesemester and compares those impressions, where applicable, to impressions gatheredafter they had completed the first problem near the beginning of the semester. Usinggrounded theory techniques to analyze the data, six central themes emerged from theimplementation: course structure, facilitation roles, student roles, group processes, coconstruction,and resources. Implications for practice and potential instructional designsolutions that may aid in future implementations are discussed

Residual Stresses in a Two-Phase Microcracking Ceramic

Residual stresses in a SiC-TiB_2 particulate composite before and after stressing have been measured using X-ray diffraction. Tensile residual stresses in the TiB_2 drop by 60% after bending stresses of 250 MPa are applied. Likewise, the compressive residual stresses in the SiC phase decrease accordingly. Such behavior is consistent with stress-induced microcracking

Residual stress measurement with high energy x-rays at the Advanced Photon Source.

Preliminary measurements with high energy x-rays from the SRI CAT 1-ID beam line at the Advanced Photon show great promise for the measurement of stress and strain using diffraction. Comparisons are made with neutron measurements. Measurements of strains in a 2 mm thick 304 stainless steel weld show that excellent strain and spatial resolutions are possible. With 200 {micro}m slits, strain resolutions of 1 x 10{sup {minus}5} were achieved