Variation of stress intensity factor through the thickness of plate

Stress intensity factor (SIF) is one of the most important parameters in fracture mechanics. Therefore there is essential request on investigation of the behavior of SIF. Due to extensive and practical usage of plate structures in components, hence the behavior of SIF through the thickness of plate has been done. The three dimensional (3D) plate has simulated in ABAQUS finite element software. Crack tip has been meshed by 20 quarter node elements. The results presented that the SIF in free surfaces of plate had minimum value and variation of SIFs approximately was constant through the thickness of plate except on free surface

Investigation of creep fatigue crack propagation in aluminium tube

Tubular structure is extensively used from domestic to aviation kind of applications. Life and safety are most considered in designing tube structure that against failure. For the last 200 years of research output and understanding, it was estimated that about 90% of metal failures were due to the external or surface defect and environmental attacks. The present work had focused on damage tolerant fatigue life prediction on aluminium cylindrical structures. Endurance tests were conducted with a constant amplitude repetitive loading at both, in room and high temperatures. A notch is introduced by wire cut machined on external surface and in a straight line with circumferential orientation to represent an external defects and flaws. Crack growth rates were measured by imaging technique. The experimental results suggested that the creep fatigue life is shorter than conventional fatigue life. The effect of stress ratio is also presented. The fully reversed with high temperature results registered the most severe damage with tremendous of life reduction

On the Crush Behavior of an Ultra Light Multi-Cell Foam-Filled Composite Structure under Axial Compression

In this article the results of experimental works pertaining to the crash behavior and crashworthiness characteristics of a novel multi-cell cost-effective crashworthy composite sandwich structure are presented. All the samples are based on the concept of the ‘triple-layered’ foam-filled block, i.e., three polyurethane foam core sheets, which are wrapped by reinforcement fiberglass woven fabric, that acts as the reinforcement face and meanwhile ties the foam layers and faces together, thus preventing catastrophic failure. The design, manufacturing, and crush testing of rectangular blocks are described. Experimental results indicate an efficient progressive collapse mechanism with high values of crushing force efficiency and specific energy absorption

Comparison of various functionally graded femoral prostheses by finite element analysis

This study is focused on finite element analysis of a model comprising femur into which a femoral component of a total hip replacement was implanted. The considered prosthesis is fabricated from a functionally graded material (FGM) comprising a layer of a titanium alloy bonded to a layer of hydroxyapatite. The elastic modulus of the FGM was adjusted in the radial, longitudinal, and longitudinal-radial directions by altering the volume fraction gradient exponent. Four cases were studied, involving two different methods of anchoring the prosthesis to the spongy bone and two cases of applied loading. The results revealed that the FG prostheses provoked more SED to the bone. The FG prostheses carried less stress, while more stress was induced to the bone and cement. Meanwhile, less shear interface stress was stimulated to the prosthesis-bone interface in the noncemented FG prostheses. The cement-bone interface carried more stress compared to the prosthesis-cement interface. Stair climbing induced more harmful effects to the implanted femur components compared to the normal walking by causing more stress. Therefore, stress shielding, developed stresses, and interface stresses in the THR components could be adjusted through the controlling stiffness of the FG prosthesis by managing volume fraction gradient exponent

Development process of new bumper beam for passenger car: a review.

Bumper beam absorbs the accidental kinetic energy by deflection in low-speed impact and by deformation in high-speed impact. The safety regulations “low-, and high-speed, and pedestrian impacts” along with new environmental restrictions “end-of-life vehicles” increased the complexity level of bumper system design. The new bumper design must be flexible enough to reduce the passenger and occupant injury and stay intact in low-speed impact besides being stiff enough to dissipate the kinetic energy in high-speed impact. The reinforcement beam plays a vital role in safety and it must be validated through finite-element analysis (FEA) and experimental tests before mass production. The careful design and analysis of bumper beam effective parameters can optimize the strength, reduce the weight, and increase the possibility of utilizing biodegradable and recyclable materials to reduce the environmental pollution. Developing the correct design and analysis procedures prevents design re-modification. On the other hand, analysis of the most effective parameters conducive to high bumper beam strength increases the efficiency of product development. Cross section, longitudinal curvature, fixing method, rib thickness, and strength are some of the significant design parameters in bumper beam production. This study critically reviews the related literature on bumper design to come up with the optimal bumper beam design process. It particularly focuses on the effective parameters in the design of bumper beam and their most suitable values or ranges of values. The results can help designers and researchers in performing functional analysis of the bumper beam determinant variables

Fatigue Crack Propagation in Aluminium 6063 Tubes

Tubular structures have extensive usage from domestic to aviation. Therefore estimate of life and safety are essential for design and use. Fatigue is one the most frequent cause for failure in components. Beside fatigue, external surfaces of structures are always in contact with environment and due to imperfection during product fabrication, surface crack may exist. Therefore surface crack is the most common form of crack in engineering structures. To overcome the fatigue problem the design approaches should be considered. The fatigue design approaches are divided in two categories which are safe life approach and damage tolerant design. Due to the importance of tubular structure and possible effect of fatigue in structural damage, the present work has focused on fatigue and fatigue crack propagation behavior in cylindrical structures. The fatigue design approaches utilized stress based safe life and damage tolerant design approach. The finite element software, ABAQUS used to analyze fatigue and determine fracture parameters. At the beginning fatigue test in finite life was carried out based on Japanese standard. The fatigue tests were done at room temperature and about 350°C under stress ratio equal to -1 and 0.1. Following experimental part, a 3-D fatigue analysis was carried out by ABAQUS. In fatigue analysis by ABAQUS, the linear material is considered and the results of finite element analysis are plotted in maximum stress versus number of cycles to failure graph. Fatigue analysis was carried out in same condition as experimental part at room temperature and 350°C under stress ratio equal to -1 and 0.1. Subsequent to fatigue analysis, the fatigue crack propagation tests were also carried out. The fatigue crack propagation test was carried out under increasing stress intensity factor or constant amplitude stress. In fatigue crack propagation test, a cracked tubular specimen was used. The crack is located in specimen by wire cut. The crack was an external and circumferential with straight front with depth of 0.37mm. The results of fatigue crack propagation were plotted in two types of graphs; first is crack length ,a, versus the number of cycles, N at each crack length and second is the crack growth rate which plotted as function of rate of crack length upon the number of cycles, da/dN versus the stress intensity factor as fracture parameter. Moreover ABAQUS was used to derive the fracture parameters. Two types 3-D tubes with crack were modeled. In first model assumed as sharp and thin crack, but in the second type the blunt crack considered. Material of tube in ABAQUS assumed to be a linear elastic and elastic prefect plastic. The results of crack modeling include fracture parameters as stress intensity factor, and Jintegral which were plotted as a function of crack front. The experimental results of fatigue showed a good agreement with finite element fatigue results. Based on fatigue results the fully reversed fatigue is more severe than fatigue with stress ratio equal to 0.1. Temperature does affect fatigue life which is shown by a decrease in yield strength and ultimate strength of material which resulted in reduction in the fatigue life of specimens with increasing temperature. The fatigue crack propagation results indicated crack growth rate in loading with stress ratio equal to 0.1 is more than stress ratio equal to -1. Crack first grew through the thickness followed by the surface of specimen. This was verified by the results from finite element that show maximum fracture parameters in the deepest point of the crack

Utilization of functionally graded materials in femoral prosthesis / Azim Ataollahi Oshkour

Total hip replacement is a highly effective surgical operation that relieves pain and restores the function of a degenerated hip joint. However, with the increasing incidence of total hip replacements, particularly among young patients, and femoral prosthesis implantation, implant designs should consider long-term survival and better performance. Minimizing the mismatch between the prosthesis and bone stiffness to reduce stress shielding and retain interface stresses within acceptable levels, can increase the longevity of total hip replacement and enhance the performance of the prosthesis. A prosthesis with adjustable stiffness may enable prosthetists to match the prosthesis and bone stiffness. Functionally graded materials have attracted much attention in the production of prosthesis with customizable stiffness. Computational modeling provides a flexible framework to examine the behavior of hip replacements, host bone, and different implant design configurations using a computer instead of conducting expensive and destructive experimental tests. ABAQUS, a finite element software, was used to analyze a femur implanted with different prostheses and determine the circumferential crack behavior in the cement layer of a total hip replacement. The cemented and cementless Charnley femoral prostheses composed of functionally graded materials were initially examined. Finite element analysis was performed on the implanted femur with prostheses made of conventional materials, such as stainless steel, and titanium alloys. Finite element analysis was then conducted on the cementless and cemented functionally graded femoral prostheses with different geometries. Circumferential cracks were located in the cement layer on the internal and external surfaces of the cement at different positions along its length from distal to proximal direction. After numerical studies, an experiment was performed using the composites and functionally graded materials composed of four metallic phases and two ceramic phases. Physical and compressive mechanical properties were then examined. Results revealed that a prosthetic material plays a key role on the strain energy density in the proximal metaphysics of the femur and on the stress distribution in the implanted femur constituents. Low-stiffness prostheses resulted in higher strain energy density in the periprosthetic femur. In the femur with functionally graded prostheses, strain energy density proportionally increased with gradient index growth. Stiffer prostheses carried more stress than less stiff prostheses. The increase in gradient index also showed an adverse relationship with the developed stress in the femoral prostheses. However, the developed stress in the bone and cement demonstrated an increasing trend with the increase in gradient index. The internal and external circumferential cracks had no significant interaction. The numerical study on the circumferential crack behavior revealed that KII was smaller than KI and KIII. Higher values of stress intensity factors were obtained at the distal part compared with that at the proximal part of the cement layer. Moreover, experimental results revealed that the abundant metallic and ceramic composites showed better mechanical properties than those of the composites with 40 wt%–60 wt% of the metal and ceramic phases. In addition, compared to pure metals, the functionally graded materials exhibited better mechanical properties, such as low Young’s modulus. Functionally graded materials also demonstrated more compressive stress and plastic deformation than the composites with more than 30 wt% ceramic phases

Mechanical and physical behavior of newly developed functionally graded materials and composites of stainless steel 316L with calcium silicate and hydroxyapatite

This study aimed to investigate the structural, physical and mechanical behavior of composites and functionally graded materials (FGMs) made of stainless steel (SS-316L)/hydroxyapatite (HA) and SS-316L/calcium silicate (CS) employing powder metallurgical solid state sintering. The structural analysis using X-ray diffraction showed that the sintering at high temperature led to the reaction between compounds of the SS-316L and HA, while SS-316L and CS remained intact during the sintering process in composites of SS-316L/CS. A dimensional expansion was found in the composites made of 40 and 50 wt% HA. The minimum shrinkage was emerged in 50 wt% CS composite, while the maximum shrinkage was revealed in samples with pure SS-316L, HA and CS. Compressive mechanical properties of SS-316L/HA decreased sharply with increasing of HA content up to 20 wt% and gradually with CS content up to 50 wt% for SS-316L/CS composites. The mechanical properties of the FGM of SS-316L/HA dropped with increase in temperature, while it was improved for the FGM of SS-316L/CS with temperature enhancement. It has been found that the FGMs emerged a better compressive mechanical properties compared to both the composite systems. Therefore, the SS-316L/CS composites and their FGMs have superior compressive mechanical properties to the SS-316L/HA composites and their FGMs and also the newly developed FGMs of SS-316L/CS with improved mechanical and enhanced gradation in physical and structural properties can potentially be utilized in the components with load-bearing application

Effect of Geometrical Parameters on the Performance of Longitudinal Functionally Graded Femoral Prostheses

This study aimed to assess the performance of different longitudinal functionally graded femoral prostheses. This study was also designed to develop an appropriate prosthetic geometric design for longitudinal functionally graded materials. Three-dimensional models of the femur and prostheses were developed and analyzed. The elastic modulus of these prostheses in the sagittal plane was adjusted along a gradient direction from the distal end to the proximal end. Furthermore, these prostheses were composed of titanium alloy and hydroxyapatite. Results revealed that strain energy, interface stress, and developed stress in the femoral prosthesis and the bone were influenced by prosthetic geometry and gradient index. In all of the prostheses with different geometries, strain energy increased as gradient index increased. Interface stress and developed stress decreased. The minimum principal stress and the maximum principal stress of the bone slightly increased as gradient index increased. Hence, the combination of the femoral prosthetic geometry and functionally graded materials can be employed to decrease stress shielding. Such a combination can also be utilized to achieve equilibrium in terms of the stress applied on the implanted femur constituents; thus, the lifespan of total hip replacement can be prolonged. 2014 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.Scopu