A new crack tip element for the phantom‐node method with arbitrary cohesive cracks

We have developed a new crack tip element for the phantom‐node method. In this method, a crack tip can be placed inside an element. Therefore, cracks can propagate almost independent of the finite element mesh. We developed two different formulations for the three‐node triangular element and four‐node quadrilateral element, respectively. Although this method is well suited for the one‐point quadrature scheme, it can be used with other general quadrature schemes. We provide some numerical examples for some static and dynamic problems. Copyright © 2007 John Wiley & Sons, Ltd.     

Cd-free buffer layers for CIGS solar cells prepared by a dry process

ZnSe buffer layers for Cu(ln,Ga)Se₂/buffer/ZnO solar cells have been prepared by metal organic chemical vapor deposition (MOCVD). Using photoassisted MOCVD, deposition temperatures down to 265°C are possible. It is shown that deposition temperatures well below 300°C are essential as well as deposition times not much longer than 3 min. Higher temperatures and longer deposition times lead to absorber degradation. With optimized buffer deposition efficiencies of 11% have been obtained on CIGS absorbers from the Siemens pilot production line.     

HF2V dissipator effects on the performance of a 3 story moment frame

In this paper, the seismic performance of the as-designed SAC Los Angeles 3 story seismic frame with rigid moment connections at the beam ends is compared with that of the same frame using semirigid connections with high force-to-volume (HF2V) lead dissipators. The presence of the gravity frames in the model is also considered. It was found that the placement of dissipators, ignoring the effect of the gravity frames, caused a 12% increase in period of the frame due to the decreased stiffness of the connections. During design level ground shaking the semi-rigid connections with HF2V dissipators have slightly lower accelerations, up to an 80% increase in peak drift, and a 200% increase in the permanent displacement compared to the as-designed case, but no structural damage is expected. When the gravity frames are considered, the floor accelerations decrease further, the peak displacements do not significantly change, but the residual story dirft ratios reduce to approximately 0.17%. This result is less than one half that of the as-designed frame, where typically gravity frame effects are not considered. The realistic analyses combining HF2V lead dissipators with gravity frames and well-designed non-structural elements creates a system with almost no structural damage and low residual displacements.     

Three-dimensional crack initiation, propagation, branching and junction in non-linear materials by an extended meshfree method without asymptotic enrichment

This paper presents a three-dimensional, extrinsically enriched meshfree method for initiation, branching, growth and coalescence of an arbitrary number of cracks in non-linear solids including large deformations, for statics and dynamics. The novelty of the methodology is that only an extrinsic discontinuous enrichment and no near-tip enrichment is required. Instead, a Lagrange multiplier field is added along the crack front to close the crack. This decreases the computational cost and removes difficulties involved with a branch enrichment. The results are compared to experimental data, and other simulations from the literature to show the robustness and accuracy of the method.     

On the numerical stability and mass‐lumping schemes for explicit enriched meshfree methods

Meshfree methods (MMs) such as the element free Galerkin (EFG)method have gained popularity because of some advantages over other numerical methods such as the finite element method (FEM). A group of problems that have attracted a great deal of attention from the EFG method community includes the treatment of large deformations and dealing with strong discontinuities such as cracks. One efficient solution to model cracks is adding special enrichment functions to the standard shape functions such as extended FEM, within the FEM context, and the cracking particles method, based on EFG method. It is well known that explicit time integration in dynamic applications is conditionally stable. Furthermore, in enriched methods, the critical time step may tend to very small values leading to computationally expensive simulations. In this work, we study the stability of enriched MMs and propose two mass‐lumping strategies. Then we show that the critical time step for enriched MMs based on lumped mass matrices is of the same order as the critical time step of MMs without enrichment. Moreover, we show that, in contrast to extended FEM, even with a consistent mass matrix, the critical time step does not vanish even when the crack directly crosses a node. Copyright © 2011 John Wiley & Sons, Ltd.     

Isogeometric cohesive zone model for thin shell delamination analysis based on Kirchhoff-Love shell model

We present a cohesive zone model for delamination in thin shells and composite structures. The isogeometric (IGA) thin shell model is based on Kirchhoff-Love theory. Non-Uniform Rational B-Splines (NURBS) are used to discretize the exact mid-surface of the shell geometry exploiting their C¹-continuity property which avoids rotational degrees of freedom. The fracture process zone is modeled by interface elements with a cohesive law. Two numerical examples are presented to test and validate the proposed formulation in predicting the delamination behavior of composite structures.     

Artificial Neural Network Methods for the Solution of Second Order Boundary Value Problems

We present a method for solving partial differential equations using artificial neural networks and an adaptive collocation strategy. In this procedure, a coarse grid of training points is used at the initial training stages, while more points are added at later stages based on the value of the residual at a larger set of evaluation points. This method increases the robustness of the neural network approximation and can result in significant computational savings, particularly when the solution is non-smooth. Numerical results are presented for benchmark problems for scalar-valued PDEs, namely Poisson and Helmholtz equations, as well as for an inverse acoustics problem.     

Sphingosine 1-Phosphate Receptor 5 (S1P5) Knockout Ameliorates Adenine-Induced Nephropathy

S1P and its receptors have been reported to play important roles in the development of renal fibrosis. Although S1P₅ has barely been investigated so far, there are indications that it can influence inflammatory and fibrotic processes. Here, we report the role of S1P₅ in renal inflammation and fibrosis. Male S1P₅ knockout mice and wild-type mice on a C57BL/6J background were fed with an adenine-rich diet for 7 days or 14 days to induce tubulointerstitial fibrosis. The kidneys of untreated mice served as respective controls. Kidney damage, fibrosis, and inflammation in kidney tissues were analyzed by real-time PCR, Western blot, and histological staining. Renal function was assessed by plasma creatinine ELISA. The S1P₅ knockout mice had better renal function and showed less kidney damage, less proinflammatory cytokine release, and less fibrosis after 7 days and 14 days of an adenine-rich diet compared to wild-type mice. S1P₅ knockout ameliorates tubular damage and tubulointerstitial fibrosis in a model of adenine-induced nephropathy in mice. Thus, targeting S1P₅ might be a promising goal for the pharmacological treatment of kidney diseases.