Papers by Keyword: Strain Concentration

Abstract: A numerical simulation model has been established to obtain the deformation, strain and stress concentration of slab narrow side. The simulated temperature profiles of slab show a agreement with the results of measured temperatures by using infrared thermal camera. Moreover, the deformation, stress and strain of the slab have been investigated systematically, especially at the slab narrow side along the thickness direction. The relationship between the reduction amount and deformation, stress and strain concentration of slab narrow face has been investigated.

Abstract: Rubber material is non-linear, hyper-elastic and incompressible. Its complex mechanical properties increase the difficulties of the theoretical calculation in large deformation. As the development of computing capacity and optical sensors, DIC (Digital Image Correlation) method has become an important method in measuring large deformation of rubber material. In this paper, DIC method was used to measure different depth of burial defective rubber in tensile test, the result, however, failed to test the burial defects of rubber sheet. In order to explore the failure mechanism, the finite element simulation test is completed using Mooney-Rivlin material model of two parameters. The undetected phenomenon is caused by rubber’s hyper elasticity and low-rigidity. The results show that DIC method can be effectively applied to the measurement and evaluation of mechanical properties of rubber-like material’s surface defects, but not its burial defects. The fact that DIC method is unable to detect the burial defects of rubber sheet should be paid more attention.

Abstract: This paper reports the design assessment carried out on a subassembly of an advanced rocket using experimental techniques. The design was very complex and critical, since a cylindrical shell had a square cutout on the axial-hoop plane interacting with a notch in the axial-radial plane. Herein, two optical techniques have been employed for assessing the interaction between the notch and the cutout, and their individual contributions to the strain-field. Initially, a photoelastic model was studied to estimate the stresses at the notch tip. Subsequently, DIC was employed for measuring strains at the notch during the ground based testing of the actual component. The outcomes of these two experiments showed that the effect of the cutout to the strain concentration was negligible due to the extra stiffness provided by other assemblies.

Abstract: In order to alleviate thermal stress of piston head, the causes of thermal stress are studied. The original piston is modified from the perspective of easing strain concentration. The thermal stress and strain fields of the original and modified pistons are analyzed with FEM. Comparison of the analysis results shows that analyzing strain concentration is an efficient way to find out the fundamental causes of high thermal stress of piston head. Thus viable approaches are proposed to solve the problem.

Abstract: Adhesive bonding of two different materials appears in many modern engineering applications, e.g.: airplanes, boats, cars etc. In many practical problems the adhesive bonding is subjected to shear loading. Therefore this is important to investigate the whole deformation process of the considered type of joints under monotonic loading, to get information about the shear strength and strain concentrations. Such concentrations lead to microdefects initiation and their further coalescence to create a main crack. The unstable crack propagation leads to final failure of the adhesive joint. The Digital Image Correlation (DIC) System - ARAMIS allows for constant monitoring of the deformation state up to the final failure. The tests were performed for bi-material specimens made of adhesively bonded PMMA and aluminum strips (Fig.1) and for pure PMMA and pure aluminum specimens. Additionally, two strain gauges on each homogeneous specimen and four on the bimaterial ones are used for strains estimations. The four point bending Iosipescu tests were performed using MTS machine with constant speed. In the first method (DIC) the ARAMIS system recorded a displacement distribution in samples with frequency 1Hz. In the second method the strains were recorded by the strain gauges - using analog output channels of the HOTTINGER data Acquisition System - MGCPlus, the current value of the load using analog output channel of the MTS machine was recorded too. The load-displacement curves were obtained for the whole deformation process and the shear strength of the joints was estimated. The energy absorption of the joints was calculated.

Abstract: The main factor of rubber fatigue was stress field. But the way is not sensitive in many cases. To clarify which factors were the main for predict the locations of fatigue crack, we analyzed the factors of stress field and strain field of rubber joint, and relations between the factors and the locations of fatigue crack, using 3D FE simulation. The result showed stress concentration was not sensitive to predict the locations of fatigue crack. The locations are close to strain concentration of rubber joint. In this paper we propose the approach of using strain concentration to predict the fatigue crack locations for rubber joint. This result is significant for the rubber joint design and the study of fatigue strength theoretic.

Abstract: In nano-imprint lithography (NIL) process, which has shown to be a good method to fabricate polymeric patterns, several kinds of pattern defects due to thermal effects during polymer flow and mold release operation have been reported. A typical defect in NIL process with high aspect ratio and low resist thickness pattern is a resist fracture during the mold release operation. It seems due to interfacial adhesion between polymer and mold. In the present investigation, FEM simulation of NIL process was carried out to predict the defects of the polymer pattern and to optimize the process by FEA. To achieve the above mentioned purpose, FEM simulation technique based on constitutive modeling of polymer with experiments was firstly investigated [1]. Secondly, the embossing operation in NIL process was investigated in detail by FEM. From the analytical results, it was found that the non-uniform flow-pattern of polymer and the applied pressure in the embossing operation induce the cavity and the drastic lateral-strain at the edge of pattern. It was also shown that the low polymer-thickness result in the delamination of polymer from the substrate. It seems that the above phenomena cause the defects of the final polymer pattern.

Abstract: Carbon nanotubes (CNTs) have been attracting attention because of their prominent mechanical and electronic properties. In this study, we investigate the deformation of a single-walled carbon nanotube (SWCNT) with a bend junction using atomistic modeling with Brenner potential to analyze strain concentration caused by macroscopic tube shape and microscopic interatomic bond structure. The simulation model consists of (8,8) and (14,0) CNTs connected with a flexion angle of 30 degrees. For geometric reasons five and seven-membered rings are introduced at the inside and outside of the bend junction. After the structure under no external load is determined, tensile load is applied to the model. Then, we analyze the strain concentration at the bend junction, and high tensile strain is observed at the inside of the bend junction. The strain at the seven-membered ring at the inside of the bend junction has higher strain compared to the neighboring rings due to the microscopic effect.

Abstract: In this paper, fracture behavior of ferroelectric ceramics under combined electromechanical loading was investigated using moiré interferometry. It is found that the influence of electric field on fracture toughness is not very larger in the case that the directions of the poling, electric field and crack extension are perpendicular to each other. When the poling direction is parallel to the crack extension direction and both are perpendicular to the electric field direction, the normal strain measured reduced faster than that calculated by FEM with and without electrical loading as the distance away from the crack tip increases. Fracture toughness decreases obviously as the electric-field intensity increases.