Papers by Keyword: Bi-Material

Abstract: Fracture analysis of crack is very essential to ensure the reliability and avoid the catastrophic failure of engineering components and structures since most of the failures start from the crack which leads to loss of life and economy. In the present study, extended finite element method (XFEM) is used to simulate the axial surface crack in bi-material pipe. Bi-material consists of two dissimilar materials with distinct properties. In this study, bi-material pipe consists of inner pipe made of steel alloy and outer pipe made of ceramic. An axial semi elliptical part through crack at different location is used for 3D linear elastic fracture mechanics (LEFM) analysis of bi-material pipe. Bi-material pipe is subjected to internal pressure and stress intensity factor (SIF) is computed at different location of crack front of semi elliptical surface crack using virtual domain extension approach.

Abstract: Interface crack is evaluated using modified quarter point crack tip displacement method. Quarter point elements around the crack tip were employed in the Finite Element (ABAQUS) analysis to determine the near crack tip grid point displacements. In this study, a technique is adopted in which the crack opening displacement of the near crack tip grid point is forced to satisfy a known constraint. The linear term in the distance around the crack tip is reduced to zero. The complex stress intensity factor for interface crack is determined using the quarter point and the displacement correlation technique. It is well observed that FEM produce a less reliable displacement approximation around interface crack tip. However, this report will show that the use of near crack tip open displacement as determined by the standard finite element method can be utilised to give satisfactory result for the interface stress intensity factors K₁ and K₂.

Abstract: Using the method of composite material complex and constructing new stress functions with complex singularity exponents, the problem of singularities near interface crack tip for mode II of orthotropic bi-material is studied. Boundary value problems of generalized bi-harmonic equations can be solved with the help of boundary conditions, then four kinds of stress singularities are deduced, respectively, such as the constant singularity at λ=-1/2, the non-constant singularity at λ=-1/2+ε , the constant oscillation singularity at λ=-1/2+iε, and non-constant oscillation singularity at λ=-1/2+c+iε. For each case, the analytic expressions for stress intensity factors near the central-penetrated interface crack tip for mode II of orthotropic bi-material are obtained.

Abstract: The purpose of this study was to verify the stresses induced by dental restoration on bi-material FEM alveolar bone model. Implanting induced stresses over the alveolar bone are studied during the past decades. With the improving computing technology, computer simulations with FEM( Finite Element Method) software are employed on investigating the stresses after the cure. An important issue about FEM calculations is the discretelized model. Single material bone model were adopt in the early stage studies. Due to the nature of human bone structure, the assumption of homogenous material over the bone is not an adequate one nowadays. Bi-material bone structure has become the mainstream of the numerical studies these years. The bones are modeled with a cancellous core surrounded by a dense cortical layer. Forces, stresses, deformations and strains are calculated by performing FEA on those digital bone models. However, the reliability of bi-material bones digital models is not verified. We built a bi-material prototype and an identical digital implanted bone model. Same boundary conditions and loads are applied on both models. The induced strains measured by strain gage agree with the computer calculated results well.

Abstract: The interval element-free Galerkin method (IEFGM) is proposed to analyze a bi-material cantilever beam, which is an interfacial mechanics problem including uncertain parameters. Interval method could be applied to study the influences of the uncertain parameters on structural responses. The IEFGM could be used to approximate the displacement fields without depending on meshes. Combining these two methods, the interval equilibrium equations are derived, and a method of dealing with the discontinuities on the interface is introduced.

Abstract: The assessment of conditions of crack initiation in a tip of a bi-material notch composed of two orthotropic materials is dealt. The assessment of the bi-material orthotropic notch stability criteria based on standard linear elastic fracture mechanics can lead to incorrect results due to a change of fracture mechanics properties. The change of the fracture mechanics properties are taken into account in the discussed stability criterion. It is shown that the criterion of this kind can qualitatively and quantitatively influence the results, and it contributes to more reliable assessment of components with geometrical and/or material discontinuity.

Abstract: A generalized expression of the stress-singularity function at the tip of artificial crack is proposed, and a formula to calculate the stress intensity factor of artificial crack is obtained in the paper. The solutions of stress singularity of a cracked bi-materials beam under uniform tension and bending were computed. The results show that the degree of stress-singularity is determined by the exponent λ at the tip of artificial crack, and the exponent λ is, not only determined by materials parameter of artificial crack but also by angle. Key words: artificial crack; bi-material; stress singularity; eigen value; stress extrapolation method

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 problem of a point dislocation interacting with an elliptical hole at the interface of two bonded half-planes is studied. Complex stress potentials are obtained by applying the methods of complex variables and conformal mapping. A rational mapping function that maps a half plane with a semi-elliptical notch onto a unit circle is used for mapping the bonded half-planes. The solution derived can serve as Green’s function to study internal cracks interacting with an elliptical interfacial cavity.

Abstract: In the present work the bond strength of two friction welded polymers was investigated when the bimaterial specimens were subjected to projectile impact at 86 ms-1. Two transparent polymer rods of Polycarbonate(PC) and Polymethylmethacrylate Acrylic(PMMA) were joined together using rotary friction welding. Specimens were cut into two different batches. In one batch the central portion of the rod specimens were removed and in the other batch the complete specimens along with their central portion were retained. When the bi-material specimens were subjected to projectile impact the cracks initiated in the comparatively brittle PMMA specimens and were able to propagate across the interface and subsequently into the PC specimen for the first batch of the specimens while the cracks were either arrested at the bi-material interface or the cracks propagated along the interface in the second batch of specimens. From the experimental work it was deduced that the crack propagation along the interface or across the interface could be a good measure of the bond strength difference of a bi-material joined using rotary friction welding process. Weak point of rotary friction welding has also been identified.