Multiphysics modeling and characterization of explosively loaded aluminum blocks

A coupled Eulerian–Lagrangian finite element simulation is made of an aluminum block of dimensions 4 × 2 × 1/2 in (101.6 × 50.8 × 12.7 mm) subjected to an intensive shock load at its top. The shock load was introduced by the detonation of plastic explosives which were attached to the top of the block. The objective is to determine the effect of the shock on the deformation history of the metallic block accounting for strain rate effects. The dynamic response of the block to the high-pressure pulse was simulated by taking into account the resulting elasto-plastic deformation, the solid–fluid interaction and the adiabatic temperature rise. The dynamics of the transient stresses below the loaded surface was captured by our model. Three aspects of the explosive shock load were accordingly examined: (i) the explosive thickness and (ii) the explosive overhang length and thickness upon the resulting deformation pattern. Upon the complete dissipation of the shock, we were able to determine the distribution of the residual stress in the principal directions. Compressive residual stresses were observed in the region at and below the surface of the loaded end. The above predictions were experimentally validated using explosively loaded aluminum blocks. The experimental findings revealed general agreement with the finite element predictions of both the deformation pattern and the residual stresses.     

Proteomics in chronic kidney disease: The issues clinical nephrologists need an answer for

A growing number of patients are recognised to have chronic kidney disease (CKD). However, only a minority will progress to end-stage renal disease requiring dialysis or transplantation. Currently available diagnostic and staging tools frequently fail to identify those at higher risk of progression or death. Furthermore within specific disease entities there are shortcomings in the prediction of the need for therapeutic interventions or the response to different forms of therapy. Kidney and urine proteomic biomarkers are considered as promising diagnostic tools to predict CKD progression early in diabetic nephropathy, facilitating timely and selective intervention that may reduce the related health-care expenditures. However, independent groups have not validated these findings and the technique is not currently available for routine clinical care. Furthermore, there are gaps in our understanding of predictors of progression or need for therapy in non-diabetic CKD. Presumably, a combination of tissue and urine biomarkers will be more informative than individual markers. This review identifies clinical questions in need of an answer, summarises current information on proteomic biomarkers and CKD, and describes the European Kidney and Urine Proteomics initiative that has been launched to carry out a clinical study aimed at identifying urinary proteomic biomarkers distinguishing between fast and slow progressors among patients with biopsy-proven primary glomerulopathies.     

Performance assessment of the suspended-load backpack

The suspended-load backpack is found to improve the energy efficiency of walking with a load in some scenarios. The objective of this study is to (i) analyze the dynamic load of the suspended-load backpack over a range of walking speeds and pack masses, and (ii) determine the optimal design parameters for the suspended-load backpack to minimize the effect of dynamic load on the efficiency of walking. A simple spring, damper and mass system is used to model the performance of the suspended-load backpack as well as the typical hiking pack. The oscillating load and phase angle are calculated over a range of loading and spring stiffness values to determine the system resonance and optimal spring stiffness design range for the suspended-load backpack. Our results reveal that the stiffness for the suspended-load backpack should be designed below one half of the resonance stiffness to minimize dynamic loads at a given walking speed. The location and magnitude of the maximum phase angle is also calculated. A performance comparison between the suspended-load backpack and a typical hiking pack demonstrates the beneficial range for the suspended-load backpack. The suspended-load backpack is found to provide significant reductions in the peak backpack load, compared with a typical hiking pack, while carrying large loads at fast walking speeds. The suspended-load backpack performs poorly for low pack loads due to in-phase oscillations between the pack and the walking person.     

Three-Dimensional Finite Element Analysis of Prosthetic Finger Joint Implants

The purpose of this study was to develop high resolution three-dimensional (3D) finite element (FE) models of the Swanson^® (No. 2) and NeuFlex^® (No. 10) joint implants to: simulate implant function; evaluate stress distributions and bending stiffness of these implants; and assess their comparative potential for fracture and range of motion (ROM) in flexion and extension. Geometric representations of the implants accurate to within 20 μm were achieved using digital laser imaging technology. Images were transferred to ANSYS 5.7 using appropriate interfacing software and 3D FE models of the implants were constructed. Hyperelastic material properties of the silicone elastomers were derived experimentally from uniaxial tensile tests on implant sections. Both implants experienced maximum von Mises stresses at 90° of flexion and minimum stresses at the neutral position of flexion (Swanson: 0°, NeuFlex: 30°). Within the reported functional ROM (33°–73°), the NeuFlex implant exhibited lower maximum von Mises stress and bending stiffness than the Swanson. The Swanson implant, which has a straight hinge, exhibited lower peak stresses and bending stiffness than the NeuFlex for flexion less than 20°. Areas of high von Mises stress for the Swanson implant included the stem–hinge junction and the peripheral zone of the body of the hinge, corresponding to clinical reports of fractures. In the NeuFlex implant, the maximum stress occurred on the dorsal surface of the hinge. Bending stiffness of the NeuFlex implant was modelled to be substantially less than that of the Swanson throughout the functional ROM (33°–73° of flexion). The resting position of the Swanson implant is at 0° of flexion. A moment was required to extend the NeuFlex implant from 30° to 0° of flexion. These results suggest that the NeuFlex may potentially facilitate flexion of the metacarpophalangeal (MP) joint, whereas the Swanson may promote a more extended position of the joint.     

On the explosive hardening of one end of a metallic block

Aluminium and mild steel plates were subjected to shock loading on one end by detonating Metabel explosive sheet. The residual stresses in the principal directions were measured using the X-ray, back reflection method, through the specimen thickness.Macro- and micro-structural analyses and micro-hardness surveys of the unloaded specimens were made to examine how the influence of explosive thickness decays with distance from the loaded surface. A central fracture under explosive loading is explained by reference to unloading waves.     

Analysis of Bimaterial Wedges Using a New Singular Finite Element

This paper is concerned with the singular stress field at the vertex of a bimaterial wedge under in-plane loading. The boundary value problem is initially formulated in terms of the complex function method. The eigenequations are obtained using the continuity conditions along the interface and the traction-free conditions along the free edges, leading to the development of explicit expressions for the singular stress and displacement fields for a general bimaterial wedge. These expressions are then used to develop a new singular finite element. This element enables the determination of the singular stress field and the associated stress intensity factors reliably and efficiently. To establish the validity of the method, test cases are examined and compared with existing solutions. The method is then applied to evaluate the effect of the wedge geometry and the elastic mismatch upon the resulting stress intensity factors.     

Carnitine supplementation accelerates normalization of food intake depressed during TPN

When total parenteral nutrition (TPN; containing glucose, fat, and amino acids; caloric ratio 50:30:20) providing 100% of the rat's daily caloric intake is given for 3-4 days, food intake rapidly decreases by approximately 85%. After stopping TPN, there is a lag period of 3-4 days before food intake returns to previous level, which appears to be related to fatty acid oxidation and fat deposition. Carnitine plays a key role in the oxidation of fatty acids, and was demonstrated to reduce fat deposition in rats receiving TPN, by increasing beta oxidation. We therefore investigated whether rats receiving TPN supplemented with carnitine may prevent either the decrease or speed up the resumption or normalization of food intake, after TPN is stopped. Fourteen adult Fischer-344 rats had a central venous catheter inserted. After 10 recovery days, controls (n = 7) were infused with TPN providing 100% of rat's daily caloric intake for 3 consecutive days, followed by 4 more days of normal saline. The carnitine group (n = 7) received the same solution, but which provided 100 mg/kg/day carnitine. Daily food intake was measured and data were analyzed using ANOVA and Student's t-test. Both parenteral solutions depressed food intake maximally by almost 90% by day 3. Carnitine accelerated the normalization of food intake by decreasing the lag period by 1 day. We conclude that the addition of carnitine enhanced the normalization of post-TPN food intake and argue that this may be on the basis of enhanced fatty acid oxidation, a substrate known to play a significant role in the anorexia induced by TPN.     

On the local elastic–plastic behaviour of the interface in titanium/silicon carbide composites

The purpose of this study is to conduct a high-resolution nonlinear finite element analysis of the elastic–plastic behaviour of titanium/silicon carbide composites subject to transverse loading. This class of metal matrix composites is designed for the next generation of supersonic jet engines and deserves careful assessment of its behaviour under thermo mechanical loads. Three aspects of the work are accordingly examined. The first is concerned with the development of a representative unit cell capable of accurately describing the local elastic–plastic behaviour of the interface in metal matrix composites under thermal and mechanical loads. The second is concerned with the determination of the influence of mismatch in the mechanical properties between the inhomogeneity and the matrix upon the induced stress fields and the plastic zone development and its growth. The third is concerned with unloading and the role played by the interface upon residual stresses. It is found that the maximum interfacial stress in the matrix appears in the case involving cooling from the relieving temperature with subsequent applied compressive loading. It is also found that the mismatch in mechanical properties between the matrix and the inhomogeneity introduces significant changes in the stress distribution in the matrix. Specifically, it is observed that the maximum radial and tangential stresses in the matrix take place at the interface. The plastic deformation of the matrix leads to a relaxation of these stresses and assists in developing a more uniform interfacial stress distribution. However, the matrix stresses and the resulting equivalent plastic strains still reach their maximum values at that interface. The results show similarities in the patterns of the interfacial stress distribution and plastic zone development for all ranges of fibre volume fractions and loading levels examined. However, they also show marked differences in both the magnitude and patterns of matrix stress distribution between the adjacent inhomogeneities as a result of interaction effects between the fibres.     

On the dynamic crack propagation in an interface with spatially varying elastic properties

This article provides a comprehensive theoretical treatment of a finite crack propagating in an interfacial layer with spatially varying elastic properties under antiplane loading condition. The theoretical formulations governing the steady state solution are based upon the use of an integral transform technique. The resulting dynamic stress intensity factor of the propagating cracks is obtained by solving the appropriate singular integral equations, using Chebyshev polynomials, for different inhomogeneous materials. Numerical examples are provided to verify the technique and to show the effect of the thickness of the interfacial layer and the material properties upon the dynamic stress intensity factor of the crack and the associated singularity transition.