Micromechanical modeling of interface damage of metal matrix composites subjected to off-axis loading

A three dimensional micromechanics based analytical model is presented to investigate the effects of initiation and propagation of interface damage on the elastoplastic behavior of unidirectional SiC/Ti metal matrix composites (MMCs) subjected to off-axis loading. Manufacturing process thermal residual stress (RS) is also included in the model. The selected representative volume element (RVE) consists of an r × c unit cells in which a quarter of the fiber is surrounded by matrix sub-cells. The constant compliance interface (CCI) model is modified to model interfacial de-bonding and the successive approximation method together with Von-Mises yield criterion is used to obtain elastic–plastic behavior. Dominance mode of damage including fiber fracture, interfacial de-bonding and matrix yielding and ultimate tensile strength of the SiC/Ti MMC are predicted for various loading directions. The effects of thermal residual stress and fiber volume fraction (FVF) on the stress–strain response of the SiC/Ti MMC are studied. Results revealed that for more realistic predictions both interface damage and thermal residual stress effects should be considered in the analysis. The contribution of interfacial de-bonding and thermal residual stress in the overall behavior of the material is also investigated. Comparison between results of the presented model shows very good agreement with finite element micromechanical analysis and experiment for various off-axis angles.     

Thermoelastic free vibration and dynamic behaviour of an FGM doubly curved panel via the analytical hybrid Laplace–Fourier transformation

The paper presents an analysis of functionally graded material doubly curved panels with rectangular planform under the action of thermal and mechanical loads. Based on the first-order shear deformation theory of modified Sanders assumptions, five coupled partially differential equations (PDEs) are established as equations of motion. Each thermo-mechanical property of the shell follows the power law distribution across the thickness, except Poisson’s ratio, which is kept constant through the panel. Assuming that four edges of the shell-panel are simply supported, a Navier-based solution is adopted to reduce the PDEs into time-dependent ODEs. Applying the Laplace transformation, the equations of motion are transformed into the Laplace domain. With the aid of analytical Laplace inverse method, solutions of stresses, strains, and displacements are obtained in time domain and expressed in explicit phrases. Dynamic, free vibration, and thermo-mechanical bending analysis of the panel is carried out for various geometries. Obtained results are validated with the well-known available data reported in the literature.     

Experimental and analytical assessment of axial crushing of circular hybrid tubes under quasi-static load

In the present article, axial crushing behavior of circular aluminum/glass–epoxy hybrid tubes is studied experimentally and analytically. 48 quasi-static axial crushing experiments are carried out on bare metal and hybrid tubes to evaluate the effect of different parameters such as metal and composite wall thicknesses and stacking sequence of composite layers on the crashworthiness characteristics. The specimens are made in two types of layups including angle ply pattern [±θ]_s and multi angle ply pattern (different ply angles). The experimental results reveal that stacking sequence has a considerable effect on crashworthiness characteristics, for example for layup [90/0/0/90], the absorbed energy is more than three times of aluminum tube with the same aluminum wall thickness. Also the aforementioned layup has better energy absorption compared to [90/90/90/90] which has been previously proposed as the best layup.     

Optimal and near-optimal test sequencing algorithms with realistictest models

In this paper, we first present the formulation and solution of the basic test sequencing problem. We then consider generalized test sequencing problems that incorporate various practical features such as precedence constraints and setup operations for tests, multi-outcome tests, modular diagnosis, and rectification. We develop various AO^* and information heuristic-based algorithms to solve these practical test sequencing problems. We also discuss the issues involved in implementation of the test sequencing algorithms for solving large problems efficiently, and show that our preprocessing techniques result in considerable speed-ups     

Consumption of Synbiotic Bread Decreases Triacylglycerol and VLDL Levels While Increasing HDL Levels in Serum from Patients with Type-2 Diabetes

To our knowledge, no reports are available indicating the favorable effects of synbiotic bread consumption on blood lipid profiles among patients with type 2 diabetes mellitus (T2DM). This study was conducted to evaluate the effects of the daily consumption of synbiotic bread on blood lipid profiles of patients with T2DM. This randomized double-blinded controlled clinical trial was performed with 78 diabetic patients, aged 35–70 years. After a 2-week run-in period, subjects were randomly assigned to consume either synbiotic (n = 26), probiotic (n = 26) or control bread (n = 26) for 8 weeks. The synbiotic bread contained viable and heat-resistant probiotic Lactobacillus sporogenes (1 × 10⁸ CFU) and 0.07 g inulin (HPX) as prebiotic per 1 g. The probiotic bread contained L. sporogenes (1 × 10⁸ CFU) per 1 g. Patients were asked to consume the synbiotic, probiotic and control breads three times a day in a 40 g package for a total of 120 g/day. Biochemical measurements including blood lipid profiles were conducted before and after 8 weeks of intervention. Consumption of the synbiotic bread, compared to the probiotic and control breads, led to a significant decrease in serum TAG (P = 0.005), VLDL-C (P = 0.005), TC/HDL-C (P = 0.002) and a significant increase in serum HDL-C levels (P = 0.01). No significant effect of synbiotic bread consumption on FPG, TC, LDL-C and non-HDL-C levels was seen compared to the probiotic and control breads (P > 0.05). Trial registry code: http://www.irct.ir IRCT201311215623N13.     

Synbiotic Food Consumption Reduces Levels of Triacylglycerols and VLDL,but not Cholesterol,LDL, or HDL in Plasma from Pregnant Women

To our knowledge, no reports are available indicating the effects of synbiotic food consumption on blood lipid profiles and biomarkers of oxidative stress among pregnant women. This study was conducted to evaluate the effects of daily consumption of a synbiotic food on blood lipid profiles and biomarkers of oxidative stress in pregnant women. This randomized, double-blind, controlled clinical trial was performed among 52 primigravida pregnant women, aged 18 to 35-year-old at their third trimester. After a 2-week run-in period, subjects were randomly assigned to consume either a synbiotic (n = 26) or control food (n = 26) for 9 weeks. The synbiotic food consisted of a probiotic viable and heat-resistant Lactobacillus sporogenes (1 × 10⁷ CFU) and 0.04 g inulin (HPX)/g as the prebiotic. Patients were asked to consume the synbiotic and control foods two times a day. Biochemical measurements including blood lipid profiles, plasma total antioxidant capacity (TAC) and total glutathione (GSH) were conducted before and after 9 weeks of intervention. Consumption of a synbiotic food for 9 weeks resulted in a significant reduction in serum TAG (P = 0.04), VLDL (P = 0.04) and a significant rise in plasma GSH levels (P = 0.004) compared to the control food. No significant effects of the synbiotic food consumption on serum TC, LDL, HDL and plasma TAC levels (P > 0.05) were observed. Trial registry code: http://www.irct.ir. IRCT201212105623N3.     

Determination of Proper Austenitization Temperatures for Hot Stamping of AISI 4140 Steel

High strength steels are desirable materials for use in automobile bodies in order to reduce vehicle weight and increase the safety of car passengers, but steel grades with high strength commonly show poor formability. Recently, steels with controlled microstructures and compositions are used to gain adequate strength after hot stamping while maintaining good formability during processing. In this study, microstructure evolutions and changes in mechanical properties of AISI 4140 steel sheets resulting from the hot stamping process at different austenitization temperatures were investigated. To determine the proper austenitization temperatures, the results were compared with those of the cold-worked and cold-worked plus quench-tempered specimens. Comparisons showed that the austenitization temperatures of 1000 and 1100 °C are proper for hot stamping of 3-mm-thick AISI 4140 steel sheets due to the resultant martensitic microstructure which led to the yield and ultimate tensile strength of 1.3 and 2.1 GPa, respectively. Such conditions resulted in more favorable simultaneous strength and elongation than those of hot-stamped conventional boron steels.     

Influences of material properties of components on formability of two-layer metallic sheets

Formability of two-layer metallic sheet is constrained by plastic instability and localized necking. Forming limit diagram (FLD) is an accepted measure of sheet metal formability. The formability of two-layer sheets depends on the material properties of their components such as strain hardening exponent, strain rate sensitivity coefficient, stiffness coefficient, and grain size. In this paper, the effects of the mentioned parameters on the FLD of two-layer sheets are investigated with a theoretical model which has been verified with an experimental approach. The results show that the forming limit of two-layer sheet lies between the forming limits of its components depends on their material properties.     

In-situ generated ZnO nanoparticles for enhanced performance of thin film nanocomposite membrane in forward osmosis process

This work developed a novel approach to the in-situ synthesis of ZnO nanoparticles to modify the polysulfone (PSf) porous membrane substrate. The zinc acetate was added to the casting solution, and ZnO nanoparticles were synthesized during phase inversion. The non-solvent pH and zinc acetate concentration controlled the ZnO synthesis and loading. Their effect on the substrates properties in terms of morphology, hydrophilicity and porosity was studied thoroughly. The result shows that the ZnO nanoparticles was not formed in acidic pH, while ZnO nanoparticles with size of 20 nm could be easily formed in basic pH. The successful synthesis of ZnO nanoparticles was investigated using FTIR and EDX analysis. The EDX images verify that in-situ synthesis led to a more uniform dispersion than conventional incorporation method. Then the effect of ZnO loading on the interfacial reaction and polyamide (PA) structure was investigated. SEM images verify the successful synthesis of a uniform and defect-free PA thin film on ZnO modified substrates. FO performance results show an enhancement in water flux and salt rejection as a result of ZnO incorporation in thin film nanocomposite (TFN) membranes, where TFN 1 wt.% in-situ membrane showed 40% higher water flux than the control TFC membrane. The porous and hydrophile substrate in TFN 1 wt.% in-situ membrane is responsible for improved separation performance. These modified membranes displayed uniform dispersion of ZnO nanoparticles within substrates, confirming that this method could effectively restrain the aggregation of the nanoparticles.     

Effect of Boundary Form Disturbances on the Frequency Response of Planar Vibrations of Piezoceramic Plates. Experimental Investigation

Strength of Materials - Experimental results for forced planar vibrations of parallelogram-shaped piezoceramic plates are presented. The concept of this study is to evaluate the potentials of...