Stress intensity factors for nozzle corner cracks

Stress intensity factors have been determined by means of the frozen stress photoelastic technique for nozzle corner cracks in pressure vessel models. The model geometry was chosen to represent a nuclear reactor vessel with a radial branch, and cracks of varying depth were introduced longitudinally. The results were compared to experimental data obtained from burst tests, thus extending their scope.     

Prediction of Process-Induced Distortions in L-Shaped Composite Profiles Using Path-Dependent Constitutive Law

In this paper, the corner spring-in angles of AS4/8552 L-shaped composite profiles with different thicknesses are predicted using path-dependent constitutive law with the consideration of material properties variation due to phase change during curing. The prediction accuracy mainly depends on the properties in the rubbery and glassy states obtained by homogenization method rather than experimental measurements. Both analytical and finite element (FE) homogenization methods are applied to predict the overall properties of AS4/8552 composite. The effect of fiber volume fraction on the properties is investigated for both rubbery and glassy states using both methods. And the predicted results are compared with experimental measurements for the glassy state. Good agreement is achieved between the predicted results and available experimental data, showing the reliability of the homogenization method. Furthermore, the corner spring-in angles of L-shaped composite profiles are measured experimentally and the reliability of path-dependent constitutive law is validated as well as the properties prediction by FE homogenization method.     

Implementation of quality by design approach in manufacturing process optimization of dry granulated,immediate release,coated tablets – a case study

The aim of this study was to optimize the process of tablets compression and identification of film-coating critical process parameters (CPPs) affecting critical quality attributes (CQAs) using quality by design (QbD) approach. Design of experiment (DOE) and regression methods were employed to investigate hardness, disintegration time, and thickness of uncoated tablets depending on slugging and tableting compression force (CPPs). Plackett–Burman experimental design was applied to identify critical coating process parameters among selected ones that is: drying and preheating time, atomization air pressure, spray rate, air volume, inlet air temperature, and drum pressure that may influence the hardness and disintegration time of coated tablets. As a result of the research, design space was established to facilitate an in-depth understanding of existing relationship between CPPs and CQAs of intermediate product (uncoated tablets). Screening revealed that spray rate and inlet air temperature are two most important factors that affect the hardness of coated tablets. Simultaneously, none of the tested coating factors have influence on disintegration time. The observation was confirmed by conducting film coating of pilot size batches.     

Formulation and Compaction of Microspheres

The factors affecting the tabletability of formulations containing uncoated and/or coated microspheres were discussed by presenting a case study. The size and shape, as well as surface properties of microspherical particles, the type and amount of coating agent, selection of the external additives, and the rate and magnitude of the pressure applied were found to be the most critical factors to be considered in order to obtain and maintain the desired drug release properties of the microspheres. It was found that microcrystalline cellulose was needed in order to produce satisfactory beads in terms of size, shape and surface characteristics. The microsphere formulations, which were found to be highly sensitive to lubrication, were more compressible than their powder forms, but produced much weaker tablets. When coated with Surelease, increasing the amount of coating on the pellets reduced the tensile strength of their compacts. Compaction of the microspheres at high velocities resulted in a decrease in the tensile strength values and an increase in the volumetric strain recovery values. Dissoultion studies revealed that, regardless of the amount of coating applied, the coated microspheres lost their sustained release properties during compaction.     

Reviewing some design issues for filament wound composite tubes

This article discusses important aspects of the design of composite tubes manufactured by filament winding. The work was divided into three parametric studies. The first study was conducted to determine the minimum length that can represent an infinite tube in hydrostatic testing. The second study was conducted in order to find the optimum wind angle of composite tubes subjected to internal pressure under different end conditions. The purpose of the last one was to study the influence of diameter and thickness on the failure pressure during tube burst tests. A progressive failure analysis was performed using ABAQUS software employing a damage model implemented by a user subroutine (UMAT). The models used were validated using experimental data obtained from tube burst tests in previous studies. The results provide a better understanding of the behavior of composite tubes under internal pressure thereby making possible to improve design practices used in industry.     

Formulation and Compaction of Microspheres

Abstract

The factors affecting the tabletability of formulations containing uncoated and/or coated microspheres were discussed by presenting a case study. The size and shape, as well as surface properties of microspherical particles, the type and amount of coating agent, selection of the external additives, and the rate and magnitude of the pressure applied were found to be the most critical factors to be considered in order to obtain and maintain the desired drug release properties of the microspheres. It was found that microcrystalline cellulose was needed in order to produce satisfactory beads in terms of size, shape and surface characteristics. The microsphere formulations, which were found to be highly sensitive to lubrication, were more compressible than their powder forms, but produced much weaker tablets. When coated with Surelease, increasing the amount of coating on the pellets reduced the tensile strength of their compacts. Compaction of the microspheres at high velocities resulted in a decrease in the tensile strength values and an increase in the volumetric strain recovery values. Dissoultion studies revealed that, regardless of the amount of coating applied, the coated microspheres lost their sustained release properties during compaction.     

Predicting corner crack fatigue propagation from cold worked holes

We predict the fatigue propagation of corner cracks from cold worked holes using three dimensional finite element models. The models account for the through thickness variation in residual stress left after cold working. The predictions are compared to experimental results in aluminum 2024-T351 and 7075-T651. The models show the evolution of P-shaped crack fronts similar to those observed in experiments. Predictions based on the initial residual stress field left after cold working were nonconservative, predicting either slower than experimental crack growth or crack growth that arrests. Predictions based on an estimate of the stable relaxed residual stress field near the hole were conservative, and predicted 5-10 times greater life than the current Department of Defense reduced initial flaw size approach.     

Modelling the orthogonal machining process using coated carbide cutting tools

In this paper finite element methods were used to determine the influence of various coated and uncoated tungsten carbide cutting tools on the machining of a nickel-based super alloy Inconel 718. Disposable coated and uncoated carbide inserts were used both experimentally and as FEA models to study how the stress distribution within different coatings and carbide grades compared to each other, under a range of cutting conditions. Simulation of an orthogonal metal cutting process was performed using FORGE2, an elasto-visco plastic FEA code. All FE models were assumed to be plane strain. The results include the stress and temperature distributions through the primary shear zone, the chip/tool contact region and the coating/substrate boundaries. The tool wear and stress results from the FE modelling agree favourably with those obtained from experimental work.     

Numerical analysis of fracture in ceramic coatings subjected to thermal loading

In this paper the general purpose finite element code ANSYS has been employed to analyse fracture in ceramic coatings subjected to thermal loading. An approach is developed in which hypothetical material properties have been considered as material data for coupled (thermal and structure) finite element analysis. These properties were chosen by assumed changes in some functional properties of ZrO₂-G.G. coatings. The aim was to evaluate the stress intensity factors in different coatings. Furthermore, to demonstrate the influence of crack length and coating geometry on the stress intensity in coatings, finite element analyses were carried out for various cases. The normalized stress intensity factors were obtained. The results showed that the shorter the crack length and the thinner the coating, the sounder the coatings. Furthermore, coatings representing a wide range of thermal and mechanical properties have a close normalized stress intensity factor values. It is also concluded that the finite element technique can be used to optimize the design and the processing of ceramic coatings.     

Analyses of route Bc equal channel angular pressing and post-equal channel angular pressing behavior by the finite element method

Equal channel angular pressing (ECAP) process provides an efficient procedure for achieving ultrafine grained microstructures with excellent mechanical properties in metallic materials. In this article, a simulation scheme for predicting the mechanical behavior during and after ECAP was proposed. The proposed scheme was applied for interstitial-free (IF) steels, which are widely used for the automobile body applications. Plastic deformation behavior during several passes of ECAP in route Bc, including such aspect as deformed geometry, corner gap, forming load and strain uniformity, was predicted. Tensile testing responses of the ECAP-processed IF steel, including strain hardening, onset of necking, and post-necking behavior, were analyzed using the finite element method and compared with the experimental results. The predicted tensile curves, ultimate tensile strength, and elongation varying with the number of ECAP passes were in good agreement with experimental results. The computational scheme developed was demonstrated to successfully predict not only the plastic deformation behavior during ECAP but also the mechanical properties of the ECAP-processed material.     

Analysis of fatigue crack growth in an attachment lug based on the weight function technique and the UniGrow fatigue crack growth model

A generalised step-by-step procedure for fatigue crack growth analysis of structural components subjected to variable amplitude loading spectra has been presented. The method has been illustrated by analysing fatigue growth of planar corner crack in an attachment lug made of Al7050-T7451 alloy.Stress intensity factors required for the fatigue crack growth analysis were calculated using the weight function method. In addition, so-called “load-shedding” effect was accounted for in order to determine appropriate magnitudes of the applied stress intensity factors. The rate of the load shedding was determined with the help of the finite element (FE) method by finding the amount of the load transferred through the cracked ligament. The UniGrow fatigue crack growth model, based on the material stress–strain behaviour near the crack tip, has been used to simulate the fatigue crack growth under two variable amplitude loading spectra. The comparison between theoretical predictions and experimental data proved the ability of the UniGrow model to correctly predict fatigue crack growth behaviour of two-dimensional planar cracks under complex stress field and subjected to arbitrary variable amplitude loading.     

Effect of punch and specimen dimensions on the confined compression behavior of S-2 glass/epoxy composites

The behavior of composite materials under transverse loading is often characterized using quasi-static experimental methods. A complete characterization requires experimentation for a range of specimen and impactor dimensions, necessitating a sizeable test matrix. However, if dimensional effects on specimen damage behavior can be understood, the number of tests required can be reduced. The present study considers confined compression testing of an S-2 glass/SC15 resin composite under quasi-static loading to understand damage initiation and propagation during penetration. A test matrix of 29 punch–specimen combinations was tested to determine the fracture behavior and applied load at failure. A finite element (FE) model of the experiments was also created to study the internal stress distributions. Characteristic fracture angles and applied stresses at failure were observed to be independent of punch–specimen dimensions. However, varying the dimensions of the punch and specimen was found to change the behavior of the internal stresses. Various failure criteria were evaluated using the numerical stress distributions to predict damage initiation. A Mohr–Coulomb compression–shear interaction on the fracture plane was found to best explain the observed experimental behavior.     

Fatigue analysis of damaged steel pipelines under cyclic internal pressure

A methodology for fatigue analysis of damaged steel pipelines under cyclic internal pressure is proposed. This methodology employs stress concentration factors, which are commonly used to modify standard S–N curves of metallic structures under high cycle fatigue loadings. Experiments are accomplished to evaluate the strain behavior of small-scale steel pipes during denting and cyclic internal pressure. A nonlinear finite element model is developed to obtain stress concentration factors induced by plain dents on steel pipes under internal pressure. Afterwards, analytical expressions are developed to estimate stress concentration factors as function of the damaged pipe geometric parameters. Finally, fatigue tests are conducted to evaluate the finite life behavior of small-scale damaged pipes under cyclic internal pressure and to validate the proposed methodology of fatigue analysis.     

Expansion of a cavity in a rubber block under unequal stresses

Elastic expansion of a small spherical void in the interior of a rubber block has been investigated by finite element analysis (FEA). The block was subjected to a far-field tensile or compressive stress while an internal pressure was applied to the cavity. The rubber was assumed to be virtually incompressible in volume and neo-Hookean in elastic behavior. Critical stress states were determined at which the void would become indefinitely large-a form of elastic instability. An applied tensile stress was found to lower the critical inflation pressure for instability, in agreement with experimental observations [1] whereas a compressive stress increased it. The critical mean stress was lowest for an isotropic stress system (when the applied tension was zero). It was higher when either compressive or tensile stresses were applied, i.e. under non-isotropic stresses, in agreement with the analysis of Hou and Abeyaratne [2]. However, the present results show a considerably smaller effect of tensile stress than predicted by Hou and Abeyaratne.     

钨合金动态力学性能的三维数值模拟研究

采用数值模拟的方法对钨合金在冲击载荷作用下的动态力学响应进行了研究。运用有限元动力分析程序建立了具有典型微观结构钨合金三维有限元单胞模型,对钨合金在拉伸载荷作用下的动态力学性能进行了数值模拟研究,分析了应变率对其力学性能的影响,给出了不同应变率条件下单胞模型的应力和应变分布云图,在与实验结果对比的基础上验证了该有限元模型的可靠性。     

Variables affecting the fatigue resistance of PVD-coated components

The effect of intrinsic properties of CrN coatings on fatigue behaviour was studied in this paper. The coating layer microhardness and the residual stresses characterising the surface film were measured and the obtained results were introduced in a numerical modelling predicting fatigue life procedure of coated components. The effect of a CrN monolayer film deposited on bulk samples, produced in 2205 duplex stainless steel, H11 tool steel or 6082 aluminium alloy was investigated. The fatigue limit of coated and uncoated samples was experimentally determined while the development of FEM models, confirmed by means of experimental tests, represents a powerful tool to predict fatigue life of coated components. The effects on the fatigue strength of coating and bulk material defects like droplets and non-metallic inclusions were considered along with the residual stress gradient characterising the coating and evaluated by means of X-ray measurements. The influence of the substrate material plastic deformation on the integrity of the coating was evaluated too.     

A micromechanical analysis to predict the cord-rubber composite properties

Both three- and two-dimensional generalized plane strain finite element analyses based on a micromechanics approach were carried out to investigate the linear and nonlinear effective composite properties as well as the stress fields. A unit cell model of cord-rubber composite subjected to different loadings was studied to predict the effective composite properties. The numerical results of effective composite properties obtained from 2D and 3D finite element analyses were compared with experimental data and other finite element results available in the literature. The effects of rubber material nonlinearity and large deformation on the effective composite properties and interface stress distributions are presented and discussed.     

5182-O铝合金塑性成形性能表征

目的 结合复杂加载状态试验、塑性和损伤断裂本构模型及有限元应用,实现AA5182-O铝合金在复杂加载状态下塑性变形和损伤断裂行为的精确表征。方法 通过拉伸、剪切等试验,研究5182-O在剪切、单向拉伸、平面应变拉伸等复杂应力状态下的力学性能,应用pDrucker方程来表征其复杂加载状态下的塑性变形和损伤断裂特性。采用逆向工程方法实现pDrucker屈服方程和pDrucker断裂准则的精确标定。将标定后的塑性本构模型和损伤断裂准则应用到ABAQUS/Explicit中,预测不同试件的塑性变形和损伤断裂情况。结果 通过有限元模拟与试验结果的对比,发现有限元仿真准确预测了5182-O在复杂加载状态下的力-位移曲线和损伤断裂情况。结论 有限元模拟与试验结果的对比表明,pDrucker方程可以实现5182-O铝合金在复杂加载状态下塑性成形性能的精确表征。标定的pDrucker方程可应用于5182-O冲压成形过程的有限元分析、模具设计和工艺优化中。     

Intensity of stress singularity for the circumferential V‐shape corner front of a three‐dimensional diamond‐like defect

Three‐dimensional diamond‐like defects with circumferential V‐shape corner fronts are often contained in engineering materials. In this paper, generalized stress intensity factors are calculated for this type of defect using a modified advanced finite element method. A super corner front element model in the global coordinates is established to capture the stress singularities along the circumferential corner front. Three‐dimensional numerical series eigen‐solutions in the element have been transformed from asymptotic expressions in the local curvilinear coordinates. The element is suitable for a sharp V‐shape corner with arbitrary opening and inclination angle. Singular stress fields near various shapes of diamond‐like defects are systematically investigated. The interaction of an embedded defect with free surface or another identical defect is also investigated. The numerical results can be used as stress intensity parameters to predict fatigue strength at circumferential corner front of a diamond‐like defect.     

L形复合材料层板热压工艺密实变形过程的数值模拟

基于 Biot 固结原理和达西定律 , 建立了二维树脂流动与纤维密实模型 , 采用有限元方法实现了 L 形层板热压成型过程树脂压力分布、 层板变形的预测。通过对 AS4 炭纤维/环氧 350126 等厚层板厚度变化的模拟结果与实验数据的对比分析 , 证明了数学模型和有限元程序的可靠性。以阳模成型 90° 铺层 S22玻璃纤维/环氧 648L 形层板为例 , 对工艺过程层板厚度变化进行了分析。模拟结果表明 : 剪切模量对拐角以及拐角与平板过渡区域的变形影响较大 ; 平板长度对拐角区域变形影响较明显 , 对平板区的变形影响较小。采用热压罐制备了 90° 铺层S22玻璃纤维/环氧 648阳模成型 L 形层板 , 实验数据表明 , 固化后层板呈现拐角区厚、 平板区薄的厚度不均现象 , 并且平板长度对拐角区厚度变化影响较显著 , 这与数值预测结果具有较好的一致性。