Out-of-Plane Deflection of Nonprismatic Curved Beam Structures Considering the Effect of Shear Deformation Solved by DQEM

The development of differential quadrature element method out-of-plane deflection analysis model of curved nonprismatic beam structures considering the effect of shear deformation was carried out. The DQEM uses the differential quadrature to discretize the governing differential equation defined on each element, the transition conditions defined on the inter-element boundary of two adjacent elements and the boundary conditions of the beam. Numerical results solved by the developed numerical algorithm are presented. The convergence of the developed DQEM analysis model is efficient.

The Elucidation of Mechanism of Local Sound Pressure Increase Phenomenon

Payloads of satellite are exposed on the severe acoustic environment at the process of lift-off and supersonic zone of a launcher. This acoustic environment excites the payload in high pressure and broad frequency band of random acoustical excitation, which may cause serious damage to the structures or instruments of the spacecraft inside. Space instruments are designed and verified to the acoustic environment by ground reverberant acoustic chamber in order to specify random vibration level at component interface and to verify the payloads are working in function and the structure does not have structural damage. The present load sound pressure specification assumes that the sound pressure interior fairing is uniformly distributed. In spacecraft system acoustic tests, local pressure increase occurs in the narrow gap between spacecraft primal structure and components facing toward the fairing wall. This acoustical environment load to the components differs from that the components were tested alone and the flight acoustic environment may not be actually simulated in the ground testing. It is important to clarify the mechanism of sound pressure increase in the narrow gap in order to predict the level of sound pressure increase. In this study, we focus to the investigation of the mechanism by basic experiment including acoustic testing and vibration modal survey. It is clarified that the main reason of the phenomenon is dominated by the acoustic cavity on the appropriate boundary condition rather than structure vibration. And more, we predict the frequency at which the sound pressure increase at the narrow gap and compare analysis results with experiment results by using Boundary Element Method (BEM).

MOAA and Topology Judgment for Mesh Construction

In this paper, the Maximum Opposite Angulation Approach (MOAA) for 3-D including the topology optimization is discussed. The MOAA algorithm is developed to generate meshes in 2-D and 3-D. The basic principles of the algorithm both in 2-D applications and in 3-D applications, is to pre-set uniformity to the initial data set to form point pairs yielding possible shortest line segments. These line segments are connected with the points providing the maximum angle for the vertex of the triangular mesh to be constructed. Thus, the algorithm provides triangular meshes having well balanced interior angles and good aspect ratios. The MOAA algorithm can be proved similar to the Delaunay’s approach in 2-D from the principle and with the quickest speed. In 3-D, it was also shown that it is much more efficient than many Delaunay class algorithms with mesh architectures preserving the topology, for uniformly organized data points. In this study, the topology optimization together with the MOAA algorithm is presented to improve the precision of reconstruction of the original surface. In this context, topology judgment for intersection problem in 3-D, distortion phenomenon, the possibility of loosing some characteristics of the original surface is thoroughly investigated.

Fatigue Reliability Based Optimal Replacement Decision of Mechanical Components

This paper introduces a maintenance decision-making strategy in the general area of replacement and reliability of mechanical components. The decision-making strategy involves the optimization of replacement interval based on fatigue failure of mechanical components. This new approach is based on the cumulative damage distribution function for evaluating mean fatigue life. By using the approach, the analytical expressions for the mean and the variance of the cumulative damage distribution under both stationary narrow-band and stationary wide-band random process are provided. The mean value and variance of the fatigue life distribution are thus evaluated to determine the optimal replacement intervals under fatigue failure. An algorithm of evaluating the mean and standard deviation of fatigue life is also presented. Therefore, the reliability of a component under random cyclic loading for a specified duration is quantified accordingly. Even though the new method introduces a great deal of complexity in the analytical models, this method can efficiently determine replacement intervals for component whose operating costs increases with use and replacement intervals for component subject to failure induced by the random process. An example is presented to demonstrate the application of the present method.

Ultrasonic Study on Crystal Orientation Effects Upon Point Defect Growth Caused by Cross Slip Under Plastic Deformation

Concerned with the longitudinal wave velocity changes under plastic deformation in pure shear state, the experimental results of longitudinal wave velocity are categorized to two types: (i) simple decreasing change tendency at polished surface specimens, and (ii) chaotic change tendency at unpolished surface specimens. In the present paper, the effects of surface roughness and crystal orientation on the amount of cross slip under plastic deformation are studied via finite element polycrystal model (FEPM) from the viewpoint of longitudinal wave velocity change showing a sensitive response to the point defects caused by cross slip.

Weight Functions for T-Stress for Edge Cracks in Thick-Walled Cylinders

This paper presents T-stress solutions for an internal edge crack in thick-walled cylinders under complex stress distributions. First, the background of the weight function method for the calculation of T-stress is discussed. Then the T-stress results for edge-cracked cylinders obtained from extensive boundary element analyses are summarized. The crack geometries analyzed cover a wide range of radius ratios and relative crack lengths. The loading cases considered in the BEM analysis for the cracked cylinder are: i) crack face pressures with polynomial stress distributions acting on the crack face and ii) internal pressure or steady state thermal loading in the cylinder. Then, the T-stress results for uniform and linearly varying crack face pressure cases are used as the reference solutions to derive weight functions for T-stress. Boundary element results of T-stress for other nonlinear stress distributions are used to validate the derived T-stress weight functions. Excellent accuracy has been achieved. The weight functions derived are suitable for obtaining T-stress solutions for thick-walled cylinders with an internal edge crack under any complex stress fields.

Plastic and Creep Analyses of the Superheater Header Tubeplate Using Linear Matching Method

In 2003 ASME PVP conference, a series of numerical procedures for integrity assessment based upon recently developed Linear Matching Method were presented [1]. A typical example of holed plate was used to verify these procedures for the evaluation of plastic and creep behaviours of complex geometry components based on linear solutions, which can be easily implemented into the commercial FE code ABAQUS through user subroutines. In this paper, a more complex 3D tubeplate in a typical AGR superheater header is analysed for the shakedown limit, reverse plasticity, ratchet limit and creep relaxation based on application of the Linear Matching Method. Both the perfectly plastic model and the cyclic hardening model are adopted for the evaluation of the plastic strain range. For the evaluation of accumulated creep strains, flow stresses and elastic follow-up factors with differing dwell times at the steady cyclic state, a creep-reverse plasticity model is adopted. The total inelastic strain range over the cycle at the steady cyclic state is calculated. By comparing these results with ABAQUS step-by-step inelastic analyses, the applicability of the methods is verified.

An Efficient Algorithm for Damage-Coupled Visco-Plastic Fatigue Model

The paper describes the development of an efficient and robust numerical algorithm for a damage-coupled visco-plastic-fatigue material model. The material chosen for the investigation is a eutectic material, Sn-Pb solder, exhibiting strain-softening behavior. The numerical algorithms employs a modified explicit method with adaptive sub-stepping based on the local error control for which the stress (constitutive) Jacobian explicit solution is derived. The algorithm is implemented in a commercial finite element (FE) code ABAQUS (Version 6.2) via its user-defined material subroutine. The validity of the algorithm is examined with several numerical examples, including (i) single-element simulations for uniaxial test, tensile creep, and fatigue simulations to attain an optimized algorithm, and (ii) two three-dimensional analyses of a miniature specimen under monotonic tensile loading and fatigue loading. The numerical examples illustrate the effectiveness of the modified explicit algorithm in predicting cyclic thermoviscoplastic behavior of a solder material. The algorithm is considered a generalized methodology that can be readily applied characterize thermoviscoplastic behavior and fatigue life of similar materials.

Prediction of Trimming Process Parameters in Aluminum Sheet Materials Using FE Method

The trimming process is an important step to achieve good dimension and shape of a final product. However, it requires a systematic study of the various parameters involved in material separation. The finite element method was utilized to simulate the trimming process of aluminum sheet materials in aspects of material properties, tooling conditions and process parameters, including different tool configurations, clearances and punch speeds. Punch load versus displacement diagrams and cut edge morphologies obtained from representative clearances and tool configurations were investigated. A two-dimensional plane strain trimming was analyzed using a rate independent material model. An experimentally measured fracture strain was utilized in FE modeling for fracture initiation and development using element deletion technique. A thermally coupled material model was tentatively tested. Results from simulations were compared with experiments and good agreement was obtained for most of the studied conditions. Optimal trimming process parameters such as specific tool configuration, clearance and punch speed are suggested.

FEM Analysis of Magnetic Field Induced by Martensitic Phase Transformation Around Fatigue Cracks in SUS 304 Stainless Steel

The present study has attempted to analyze the distributions of vertical magnetic flux density Bz above growing fatigue cracks subjected to various stress ratios R in SUS 304 stainless steel in which plasticity-induced martensitic transformation has occurred at room temperature in air. FEM calculations have been made to obtain Bz distributions above fatigue cracks by using composite permanent magnet models. The martensitic transformation regions around fatigue cracks were modeled as composites of permanent magnets having different B-H properties varying according to the content of α′ martensitic phase transformed. The resultant distributions of leakage magnetic flux density above fatigue cracks obtained by FEM agree well with those obtained by experiments.