On Question of Metals’ Plasticity

Straightforward and reverse descriptions are used to describe the metal’s plasticity zone. For the straightforward descriptions of the hardening zone, the “reference” point is the relative deformation εy corresponding to the yield strength σy. The deviation of the relative deformations in the metal hardening zone is measured relative to εy, and the deviation of the normal stresses is measured relative to σy. For the reverse descriptions of the metal hardening zone, the “reference” point is the relative deformation εu corresponding to the ultimate strength σu. The deviation of the relative deformations in the metal hardening zone is measured relative to εu, and the deviation of the normal stresses is measured relative to σu.

Flat-detector computed tomography evaluation in an experimental animal aneurysm model after endovascular treatment: A pilot study

We compared flat-detector computed tomography angiography (FD-CTA) to multislice computed tomography (MS-CTA) and digital subtracted angiography (DSA) for the visualization of experimental aneurysms treated with stents, coils or a combination of both. In 20 rabbits, aneurysms were created using the rabbit elastase aneurysm model. Seven aneurysms were treated with coils, seven with coils and stents, and six with self-expandable stents alone. Imaging was performed by DSA, MS-CTA and FD-CTA immediately after treatment. Multiplanar reconstruction (MPR) was performed and two experienced reviewers compared aneurysm/coil package size, aneurysm occlusion, stent diameters and artifacts for each modality. In aneurysms treated with stents alone, the visualization of the aneurysms was identical in all three imaging modalities. Residual aneurysm perfusion was present in two cases and visible in DSA and FD-CTA but not in MS-CTA. The diameter of coil-packages was overestimated in MS-CT by 56% and only by 16% in FD-CTA compared to DSA ( p < 0.05). The diameter of stents was identical for DSA and FD-CTA and was significantly overestimated in MS-CTA ( p < 0.05). Beam/metal hardening artifacts impaired image quality more severely in MS-CTA compared to FD-CTA. MS-CTA is impaired by blooming and beam/metal hardening artifacts in the visualization of implanted devices. There was no significant difference between measurements made with noninvasive FD-CTA compared to gold standard of DSA after stenting and after coiling/stent-assisted coiling of aneurysms. FD-CTA may be considered as a non-invasive alternative to the gold standard 2D DSA in selected patients that require follow up imaging after stenting.

Effect of Weld Metal Hardening Property on Deformation Behavior and Crack Driving Force of Mismatched Welded Joint

Effect of weld metal hardening property on the deformation behavior and crack driving force of strength mismatched welded joint with crack has been investigated using finite element method under plain strain condition. The results show that when the apply load is small, there is only small scale deformation around the crack tip, the whole structure is still in linear or small scale yielding condition therefore the weld metal hardening property has no significant effect on crack driving force. As the applied load increasing, the deformation region enlarges and at the same time the deformation level around the crack tip deepens, the increasing of weld metal hardening property decreases the local deformation level, consequently leading to the decreasing of the crack cracking force.