Tai-Ran Hsu

Finite Element Formulation for Two-Dimensional Inverse Heat Conduction Analysis

This paper presents a finite element algorithm for two-dimensional nonlinear inverse heat conduction analysis. The proposed method is capable of handling both unknown surface heat flux and unknown surface temperature of solids using temperature histories measured at a few discrete points. The proposed algorithms were used in the study of the thermofracture behavior of leaking pipelines with experimental verifications.

Reliability in MEMS Packaging

Cost effective packaging and robust reliability are two critical factors for successful commercialization of MEMS and microsystems. While packaging contributes to the effective production cost of MEMS devices, reliability addresses consumers confidence in and expectation on sustainable performance of the products. There are a number of factors that contribute to the reliability of MEMS; packaging, in particular, in bonding and sealing, material characterization relating to operating and environmental conditions, credible design considerations, the techniques for mitigating intrinsic stresses/strains induced by fabrications and testing for reliability are a few of these factors. This paper will offer an overview of these factors with proposed resolutions to issues relating to the reliability of these products

Packaging design of microsystems and meso-scale devices

This paper will present an overview on electromechanical packaging of microelectromechanical systems (MEMS) and microsystems such as microsensors, actuators, and fluidics. Technical problems and major issues related to packaging design will also be presented and discussed.

Mechatronics. An overview

Mechatronics is a synergy of several engineering disciplines. It relates to the design and manufacture of intelligent electromechanical products and devices. Goods and services that are produced by using Mechatronics principles have become an intimate part of human lives in modern civilization. Mechatronics has become the backbone for sustaining high standard of living of people, as well as a nations competitiveness in the global marketplace. Demands for engineers with adequate knowledge and experience in Mechatronics have drastically increased in the last decade. This paper attempts to offer readers an overview on this emerging engineering process.

Fracture toughness of coal under quasi-static and impact loading

Abstract The fracture toughness of specimens of Canadian coal, expressed as k q , was determined under both quasi-static and dynamic loading conditions. In all tests, a wedge loaded compact tension (WLCT) specimen was used. The quasi-static tests were carried out in a servohydraulic testing machine while in the dynamic testing, a Split Hopkinson Bar was used. Also studied was the effect of orientation of the crack with respect to the coal seam. Loading rates ranging from 0.1 MPa √m/sec. to 6 × 10 4 MPa √m/sec. were investigated. The results show a large increase of over one order of magnitude between k q in the quasi-static and that obtained at high loading rates.

A finite element algorithm for creep crack growth

Abstract A finite element algorithm involving the “Breakable element” concept is proposed for the prediction of the growth of a crack in a solid subject to combined thennoelastic-plastio-creep load. The unique advantage of this algorithm is its ability to provide detail stress and strain distributions, the kinematics of the inelastic zones, as well as the profiles of the growing crack. A numerical example with three assigned effective rupture strains as fracture criteria, is included to illustrate these special features.

Investigation of dynamic JId for alloy steel weldments using the split Hopkinson bar

The fracture toughness parameter JId, under dynamic loading conditions, was determined for weldments of HY80 and QT28 alloy steels using a split Hopkinson bar technique. JId was obtained for the fusion zone, the heat-affected zone, and the base metal for these steels as a function of temperature in the range of −80 to 25°C and at loading rates of ˙K = 106 MPa√m s−1. Wedge loaded compact tension specimens were loaded in a split Hopkinson bar. The onset of stable crack growth was determined by using a strain gage that was attached ahead of a fatigue crack. The results show that, at −80°C, fracture with limited stable crack growth takes place, while for all other testing conditions considerable ductility precedes fracture of these alloys.

Thermomechanical coupling effects on fractured solids

An analytical model is presented to predict the temperature field induced in a fractured solid by mechanical loadings. The heat conduction equation used to compute the temperature field consists of three separate terms that account for the coupling effects. These are the thermoelastic, thermoplastic and thermofracture coupling terms. Finite element formulations were used for the numerical solutions of a case study. This case study involved experimental assessments of temperature rises near the tip of a stationary crack when subjected to an impact load that attempted to open the crack surfaces. Good correlations of analytical and experimental results were obtained. The measurable temperature rises in a fractured solid suggested that the coupling effect may be significant enough to influence the fracture characteristics of a solid; in particular, if the bulk temperature of the solid is close to the transition temperature from the brittle to ductile fracture mode or vice versa.

A general treatment of creep crack growth

Abstract A theoretical model for creep crack based on energy balance criterion in the fracture process region is proposed in the present paper. A concept based on the dissipation of thermoelastic-plastic-creep flux into the fracture process region is introduced from which a generalized power integral Cg* was derived. This integral when is used in conjunction with the tearing modulus and other material parameters can characterize the crack growth behaviour in solids subject to general thermomechanical loadings. The analytical results computed by the proposed model have shown excellent agreement with some experimental results published by other prominent researchers.

On thermofracture behaviour of leaking thin-wall pipes

Abstract The finite element method is used to assess the fracture behaviour of thin-wall pipes involving leaking through-line cracks. The thermal effect due to the throttling process of leakage of the pressurized medium in the pipe is considered in the analysis. The fracture behaviour of the pipe is characterized by J- integrals modified to incorporate the above thermal effect. The analytical procedure described in this paper can be used to predict the critical loading conditions for runaway cracks in leaking pipelines.