High-resolution 3D weld toe stress analysis and ACPD method for weld toe fatigue crack initiation

Weld toe fatigue crack initiation is highly dependent on the local weld toe stress-concentrating geometry including any inherent flaws. These flaws are responsible for premature fatigue crack initiation (FCI) and must be minimised to maximise the fatigue life of a welded joint. In this work, a data-rich methodology has been developed to capture the true weld toe geometry and resulting local weld toe stress-field and relate this to the FCI life of a steel arc-welded joint. To obtain FCI lives, interrupted fatigue test was performed on the welded joint monitored by a novel multi-probe array of alternating current potential drop (ACPD) probes across the weld toe. This setup enabled the FCI sites to be located and the FCI life to be determined and gave an indication of early fatigue crack propagation rates. To understand fully the local weld toe stress-field, high-resolution (5 mu m) 3D linear-elastic finite element (FE) models were generated from X-ray micro-computed tomography (mu-CT) of each weld toe after fatigue testing. From these models, approximately 202 stress concentration factors (SCFs) were computed for every 1 mm of weld toe. These two novel methodologies successfully link to provide an assessment of the weld quality and this is correlated with the fatigue performance

Development of explosive welding techniques for fabrication of regeneratively cooled thrust chambers for large rocket engine requirements Final report, 28 Jun. 1967 - 15 Sep. 1970

Explosive welding techniques in fabricating regeneratively cooled thrust chambers for large rocket engine requirements including ultrasonic inspection, metallography, and burst testin

The influence of copper on the properties of ductile iron for producing centrifugally cast rolls

An intentional change in material properties is an important condition for castings production. It is one way how to meet the casting requirements of how to adapt the material properties to the operating conditions. Centrifugally cast rolls are multi-layer rollers, castings. The working layer of the barrel is called the "shell" and the body of the roll and the necks rolls are called "core". The article deals with the influence of the properties of the core iron. Earlier laboratory experiments were primary analysed for metallographic analysis and mechanical properties. These data were compared back to the experiments. The results of these laboratory working were later applied in the operating conditions of the roll foundry Vitkovitcke slevarny, spol. s r.o. The spun cast roll produced with the applied metallurgical processing change was supplied to the hot strip mill. There were monitored the positive effect of the change of the metallurgical process of the production of the core iron on the useful properties of the centrifugally cast roll. The experiment was done in order to increase the mechanical properties of ductile pearlite ductile iron. The copper in these core iron material increases the hardness and strength primarily.Web of Science18310610

Dynamic Scenarios of the Formation of Martensite with the {110} Habits in the Ni50Mn50 Alloy

Martensitic transformation B2–L10 in the ordered alloy Ni50Mn50, which occurs at comparatively high temperatures (980–920 K), is discussed with the use of dynamic concepts of the wave control of the threshold deformation. The proximity of the observed orientations of martensite-crystal habits (and of twin boundaries) to the planes of the {110} family makes it possible to use the longitudinal waves along the axes 〈001〉 (in the basis of the initial phase) as the driving factors. It is shown that at temperatures of the onset of the transformation there is a satisfactory correspondence between the calculated and experimental data on the tetragonality of martensite and on the volume effect. The opportunity of different dynamic scenarios of the formation of the final phase is noted, namely, of separate crystals; layered structures, in which the crystals of martensite with the identical orientation relationships alternate with the untransformed regions of austenite; and packets of pairwise-twinned crystals. Examples are given of morpho-types corresponding to these scenarios. © 2019, Pleiades Publishing, Ltd

Elementary metallography

Materials and Processes 1 (MET 141) is offered to freshmen by the Mechanical Engineering Department at Purdue University. The goal of MET 141 is to broaden the technical background of students who have not had any college science courses. Hence, applied physics, chemistry, and mathematics are included and quantitative problem solving is involved. In the elementary metallography experiment of this course, the objectives are: (1) introduce the vocabulary and establish outlook; (2) make qualitative observations and quantitative measurements; (3) demonstrate the proper use of equipment; and (4) review basic mathematics and science

Microstructures and mechanical properties of pure tantalum processed by high-pressure torsion

A body-centred cubic (BCC) structure metal, tantalum, was processed by high- pressure torsion (HPT) at room temperature with different numbers of rotations. The microstructural evolution was studied by electron backscatter diffraction (EBSD). The grain sizes were significantly refined at the disk edge area in the early stages of deformation (N = 0.5) but tended to attain saturation after the numbers of rotations was increased to N = 5. As the deformation continued, some coarse grains appeared in the disk edge areas and it appeared that there was structural recovery at the expense of grain boundary migration in the tantalum during HPT processing. Microhardness measurements showed the hardness gradually evolved towards a more homogenized level across the disk surfaces as the numbers of rotations increased. The hardness level after N = 10 turns was slightly lower than after N = 5 turns, thereby indicating the occurrence of a recovery process after 5 turn

Creep degradation in oxide-dispersion-strengthened alloys

Oxide dispersion strengthened Ni-base alloys in wrought bar form are studied for creep degradation effects similar to those found in thin gage sheet. The bar products evaluated included ODS-Ni, ODS-NiCr, and three types of advanced ODS-NiCrAl alloys. Tensile test specimens were exposed to creep at various stress levels at 1365 K and then tensile tested at room temperature. Low residual tensile properties, change in fracture mode, the appearance of dispersoid-free bands, grain boundary cavitation, and internal oxidation in the microstructure were interpreted as creep degradation effects. This work showed that many ODS alloys are subject to creep damage. Degradation of tensile properties occurred after very small amounts of creep strain, ductility being the most sensitive property. All the ODS alloys which were creep damaged possessed a large grain size. Creep damage appears to have been due to diffusional creep which produced dispersoid-free bands around boundaries acting as vacancy sources. Low angle and possibly twin boundaries acted as vacancy sources