Key Engineering Materials Vols. 462-463

Abstract: Failure of mechanical members largely depends on the size and the development of plastic deformation from the strain concentration parts. In order to evaluate this plastic deformation of mechanical members, we pay attention to the surface temperature that is generated by plastic deformation. Most of the plastic energy exhausted by plastic deforming is converted into heat. Therefore, the heat generation represents the macroscopic plastic deformed intensity. In this report, the tensile deformation tests by using the plate specimen with a center crack were performed and the distributions of surface temperature under the plastic deformation and crack propagation were measured by the thermocouple and the infrared thermo camera. Furthermore, FE elasto-plastic analysis couples with transient heat conduction was performed. The analytical results were good agreement with the experimental ones and it was shown that the infrared thermography method was effective non-contact measurement system as the macroscopic evaluation of the plastic deformation.

Abstract: In general, weight reduction will always lower the strength of the specimen. The primary purpose of this paper is weight reduction of lateral plate of rescue robot without causing the strength of it by using the Boundary Element Method (BEM). The dynamical loading conditions are performed before and after weight reduction. The numerical results of the stress distribution and the plastic deformation along the center line (interface) of the lateral plate show that the endure limits of the plate before and after weight reduction are almost the same and therefore, will not lower the strength of the plate.

Abstract: In this study, strength and fracture toughness of epoxy adhesively bonded scarf joints of dissimilar adherends, namely SUS304 stainless steel and YH75 aluminium alloy are examined on several scarf angles and various bond thicknesses under uniaxial tensile loading. Scarf angles, θ = 45°, 60° and 75° are employed. The bond thickness, t between dissimilar metals is controlled to be ranged between 0.1 mm to 1.2 mm. Finite element (FE) analysis is also executed to investigate the stress distributions in the scarf joints by ANSYS 11 code. From analytical solutions, stress singularity exists most pronouncedly at the steel/adhesive interface corner of joints having 45° to 75° scarf angle. This is not only in agreement with the FE analyses results but also confirmed by fracture surfaces observation wherein the fracture has always been initiated at this point. The strength of scarf joints increases as the bond thickness decreases. Interface corner toughness, Hc approach can be applied when predicting the failure stress of scarf joints. Besides, for scarf joints with an interfacial crack, the fracture toughness, Jc values are independent of bond thickness and less sensitive to adherends. Moreover, Jc increases as mode mixity increases.

Abstract: The high pressure waterjet is widely applied for mine industry, mechanical manufacture, environmental engineering, and medicine field due to its particular characteristic. Recently, the application of high pressure waterjet for gas drainage in mine has been receiving increasing attention with the development of exploitative technology. The micro-damage mechanism of coal under high pressure water jet is key to drain gas effectively. Based on damage mechanics and rock dynamics, the paper analyzed the micro-structure deformation and damage of rock and the impulsive effect under high pressure water jet and developed the dynamic model. Further, on the assumption of that rock was homogeneous and isotropic, a computational model was established based on the Arbitrary Lagrangian Eulerian (ALE) fluid-solid coupling penalty function method. The rock damage under high pressure water jet was simulated by the dynamic contact method. The results showed that the damage and breakage of ruck was mainly attributed to impacting effect and was characterized by local effect, and the evolvement of rock breakage went through three stages and the figure of rock breakage trended a funnel. On the whole, numerical results agreed with experimental results.

Abstract: The present study focuses on investigation of the adhesive phenomenon of gecko with viscoelasticity using the finite element method. By simplifying a single spatulae as a flat-ended cylinder in contact with a rigid substrate, a model is devised to study the critical radius under which the stress becomes uniform for the adhesive structure. Furthermore, viscoelasticity is taken into consideration in the simulation model instead of elasticity. The critical cylinder radii determined are in agreement with theoretical calculations and experimental data.

Abstract: The evolvement of rock fracture is a complicated and nonlinear dynamic problem. On the assumption that rock is homogeneous and isotropic, a numerical model was developed to simulate rock fracture under high pressure water jet based on continuum damage mechanics and nonlinear finite element method. The dynamic effect of rock was simulated by the dynamic contact method under high pressure water jet. The numerical simulation results showed that rock failure occurred within several milliseconds and the evolvement of it was for step under high pressure water jet and that the stress propagation in rock rapidly decayed with the distance from the jet centre. On the whole, the numerical results clearly exhibited the process of rock fracture and the extent of the water jet under high pressure water jet. It was important to the application of jet cutting rock theory and the development of water jet technology.

Abstract: The fatigue performance and durability of the reinforced concrete (RC) beams strengthened with fibre reinforced polymer (FRP) laminates is an advanced research topic in civil engineering. The crack propagation life is the dominant part of the whole fatigue life of the cracked RC members strengthened with FRP laminates under cyclic loads. In this paper, a theoretical and experimental study was conducted to investigate the rule of the fatigue crack propagation of the RC beams strengthened with carbon FRP (CFRP) under constant cyclic bending load. A total of 5 RC beams with sizes 1850×100×200mm strengthened with CFRP were tested. The results show that it is possible to divide the process of the crack propagation into three distinct phases, including crack initiation and then quickly propagation (Phase I), stable propagation and then rest (Phase II) and unstable propagation (Phase III). In accordance with Paris-Erdogan Law, a semi-empirical equation was developed to predict the crack propagation rate. The empirical coefficients of the equation were obtained from the fatigue test results. To validate this equation, the predicted fatigue life of crack propagation calculated by it is compared with the data obtained from tests. It shows the agreement is good.

Abstract: Fatigue life of automotive lower suspension arm has been studied under variable amplitude loadings. In simulation, the geometry of a sedan car lower suspension arm has been used. To obtain the material monotonic properties, tensile test has been carried out and to specify the material mechanical properties of the used material, a fatigue test under constant amplitude loading has been carried out using the ASTM standard specimens. Then, the results used in the finite element software to predict fatigue life has been evaluated later to show the accuracy and efficiency of the numerical models which they are appreciated. The finite element analysis tool is therefore proved to be a good alternative prior to the further experimental process. The predicted fatigue life from the simulation showed that Smith-Watson-Topper model provides longer life than Morrow and Coffin-Manson models. This is due to the different consideration for each strain-life model during life calculations.

Abstract: A mathematical model of the longitudinal flexibility of a continuously welded railway track and the methodology for the analysis of the longitudinal displacement of rails under the effects of passing trains is developed to investigate the longitudinal behavior of rails. The purpose of this analysis is to explore the changes of longitudinal stress distribution in the rails due to mechanical loading applied by a travelling train. A half track system is used to derive the equations required to obtain the magnitude of deflection and force of rails and these values are scaled to produce the displacement pattern using the method of superposition. The mathematical model is translated into MATLAB and validation of the program is verified through comparisons of displacement patterns generated by a computer software LONGIN. Analysis of a straight track due to train braking was performed over a track length of 1000 m. The longitudinal displacement obtained showed that maximum longitudinal displacement occur in the middle of the track at the distance of 570 m which is in direct agreement with the published result.

Abstract: It was investigated that the influences of the peeling behavior of adhesive tapes in peeling tests on IC chip pick-up performance. Needles peel off an IC chip with an adhesive film from the base material in the pick-up process, by sticking out the backside of the base material. In the case that the peeling forces of the adhesive tape decrease as the peeling speeds increase in peeling tests, only two kinds of behaviors were observed in pick-up test; the peeling propagated little and the IC chip was not peeled off under critical needle displacement while the pick-up was completed instantaneously over critical needle displacement. In the case that the peeling forces of the adhesive tape increase as the peeling speeds increase, the pick-up time decreased as the needle displacement increased. As a result, it can be concluded that the needle displacement where the peeling propagates instantaneously is critical for succeeded pick-up if the peeling forces of the adhesive tape decrease as the peeling speeds increase. If the peeling forces of the adhesive tape increase as the peeling speeds increase, the information of peeling speeds at each needle displacement are needed to estimate how long it takes to pick-up a chip.