Papers by Author: A. Zulkifli

Abstract: The objectives of this study are to determine the stress intensity factor (SIF) for different surface crack size of the lumbar vertebra and the probability of failure associated with finite element method. In this work, all the model components were meshed using the tetrahedral solid element. In order to simplify the model, all the spinal components were modeled as an isotropic and elastic material. Monte Carlo Simulation (MCS) technique was performed to conduct the probabilistic analysis using a probabilistic module in ANSYS with attempt for 100 trials. The results are observed that the maximum SIF were found in the end of crack path with 0.53 MPa.m^1/2 and the corresponding probability of failure for the model is 1.22%. Sensitivity analysis had been revealed that the crack size was sensitive to the maximum stress and maximum SIF output parameters with correlation 0.989 and 0.811 respectively. The current probabilistic study is useful as a tool to understand the inherent uncertainties and variations in biological models.

Abstract: The objectives of this study were to determine the stress concentration of the lumbar vertebra and the probability of failure associated with finite element method. The lumbar vertebra model was constructed in SolidWorks software and imported by ANSYS software for the analysis. In this work, all the model components were meshed using the tetrahedral solid element (SOLID186). In order to simplify the model, all the spinal components were modeled as an isotropic and elastic material. Monte Carlo Simulation (MCS) technique was performed to conduct the probabilistic analysis using a built-in probabilistic module in ANSYS with attempt for 100 trials. The results were observed that the highest stress concentrations were found in the adjacent posterior vertebral body with 1.2117 MPa and the corresponding probability of failure for the model is 3%. Sensitivity analysis had been revealed that the force applied to the facet (FORFCT) variable was sensitive to the stress and displacement output parameters and need to be emphasized. The current probabilistic study was very useful as a tool to understand the inherent uncertainties and variations in biological structures.

Abstract: This paper presents a non-linear numerical investigation of surface cracks in round bars under tension stresses by using ANSYS finite element analysis (FEA). Due to the symmetrical analysis, only quarter finite element (FE) model was constructed and special attention was given at the crack tip of the cracks. The surface cracks were characterized by the dimensionless crack aspect ratio, a/b = 0.6, 0.8, 1.0 and 1.2, while the dimensionless relative crack depth, a/D = 0.1, 0.2 and 0.3. The square-root singularity of stresses and strains were modeled by shifting the mid-point nodes to the quarter-point locations in the region around the crack front. The proposed model was validated with the existing model before any further analysis. The elastic-plastic analysis under tension loading was assumed to follow the Ramberg-Osgood relation with n = 5 and 10. J values were determined for all positions along the crack front and then, the limit load was predicted using the J values obtained from FEA through the reference stress method.

Abstract: The simplification of two dimensional approaches in singular finite elements has promoted the method to be used in the formulation of stress intensity factor (SIF) of multiple cracks in finite body. The effect of shielding and amplification are considered in defining the SIF. As been observed, the current available analytical approximations are more restricted to several assumptions. The more accurate and less restricted method has motivated this study. This paper presents the investigation of singular finite elements applied in two dimensional finite element models subjected to different crack-width ratio and cracks interval ratio. The newly finite element formulations are resulted with good agreement with theoretical statement compared to analytical solution. The weak points of presented analytical solution are discussed regards to the influence of crack width ratio and cracks interval ratio.