Bifurcation analysis based on a material model with stress-rate dependency and non-associated flow rule for fracture prediction in metal forming

Recent increasing application of advanced high-strength metals causes grow-ing demand for accurate fracture prediction in metal forming simulation. However, since the construction of objective and reliable fracture prediction method is generally difficult, essential progress in fundamental theory that supports evolution of fracture rediction framework is required. In this study, a fracture prediction framework based on the bifurcation theory is pre- sented. The main achievement is a novel material model based on stress-rate dependency related with non-associate flow rule. This model is based on non-associated flow rule with independent arbitrary higher-order yield function and plastic potential function for any anisotropic materials. And this formulation is combined with the stress-rate depen- dency plastic constitutive equation, which is known as Ito-Goya model, to construct a generalized plastic constitutive model in which non-normality and non-associativity are reasonably considered. Then, by adopting the three-dimensional bifurcation theory, which is known as the 3D localized bifurcation theory, more accurate prediction of the initiation of shear band is realized, leading to general and reliable construction of forming limit dia- gram. Then, by using virtual material data, numerical simulation is carried out to exhibit fracture limit diagram for demonstrating the generality and reliability of the proposed methodology. In particular, the effect of stress-rate dependency on the bifurcation analy- sis is investigated, and the order of the yield function is used to investigate the influence on the forming limit prediction

Percutaneous Sacroplasty for Sacral Metastatic Tumors Under Fluoroscopic Guidance Only

Percutaneous sacroplasty is a safe and effective procedure for sacral insufficient fractures under CT or fluoroscopic guidance; although, few reports exist about sacral metastatic tumors. We designed a pilot study to treat intractable pain caused by a sacral metastatic tumor with sacroplasty. A 62-year-old man and a 38-year-old woman with medically intractable pain due to metastatic tumors of S1 from lymphoma and lung cancer, respectively, underwent percutaneous sacroplasty. Over the course of the follow-up period, the two patients experienced substantial and immediate pain relief that persisted over a 3-month and beyond. The woman had deposition of PMMA (polymethyl methacrylate) in the needle track, but did not experience significant symptoms. No other peri-procedural complications were observed for either patient

Enhancement of Both Long-Term Depression Induction and Optokinetic Response Adaptation in Mice Lacking Delphilin

In the cerebellum, Delphilin is expressed selectively in Purkinje cells (PCs) and is localized exclusively at parallel fiber (PF) synapses, where it interacts with glutamate receptor (GluR) δ2 that is essential for long-term depression (LTD), motor learning and cerebellar wiring. Delphilin ablation exerted little effect on the synaptic localization of GluRδ2. There were no detectable abnormalities in cerebellar histology, PC cytology and PC synapse formation in contrast to GluRδ2 mutant mice. However, LTD induction was facilitated at PF-PC synapses in Delphilin mutant mice. Intracellular Ca2+ required for the induction of LTD appeared to be reduced in the mutant mice, while Ca2+ influx through voltage-gated Ca2+ channels and metabotropic GluR1-mediated slow synaptic response were similar between wild-type and mutant mice. We further showed that the gain-increase adaptation of the optokinetic response (OKR) was enhanced in the mutant mice. These findings are compatible with the idea that LTD induction at PF-PC synapses is a crucial rate-limiting step in OKR gain-increase adaptation, a simple form of motor learning. As exemplified in this study, enhancing synaptic plasticity at a specific synaptic site of a neural network is a useful approach to understanding the roles of multiple plasticity mechanisms at various cerebellar synapses in motor control and learning

Fracture prediction with a material model based on stress-rate dependency related with non-associated flow rule

In this paper, a novel material model for anisotropic metals is proposed. Fracture prediction using the proposed model is based on stress-rate dependency related with non-associated flow rule in which an arbitrary order function for both the yield and plastic potential functions are used. In addition, an explicit formulation of the equivalent plastic strain increment that is plastic-work-conjugated with the equivalent stress is also presented. Then, fracture prediction analyses are conducted by using the 3D local bifurcation theory