Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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An innovative fixture for testing the crashworthiness of composite materials
Get PDFDespite the growing diffusion of composite materials in automotive and aerospace sectors, a standard procedure for testing their crashworthiness has not been developed yet. At present, the international standards for testing composite materials under impact conditions are not adequate to test their crush behavior.
In this paper, a procedure for measuring the energy absorption due to the compressive crushing of a composite flat specimen, along its mid plane, is proposed. The experimental setup requires a fixture to hold the specimen and to avoid its buckling and an instrumented drop weight tower to obtain the force-displacement curves with the aim of calculating the Specific Energy Absorption.
The paper will describe the adopted test procedure and some of the features of the newly developed experimental setup. The effectiveness of the procedure is demonstrated by testing several glass fiber-epoxy specimens under different impact energies
Mechanical performance of intelligent asphalt mixture utilizing rejuvenator encapsulated method
Get PDFIn this study, in order to evaluate the effects of heavy vacuum slops (H.V.S) as rejuvenator and nano-Zycosil as an anti-stripping agent on used encapsulation method and mechanical performance of asphalt mixture samples, scanning electron microscopy (SEM), computerized tomography (CT) scan and thermal gravimetric (TG) analyses and also, indirect tensile strength (ITS) and indirect tensile fatigue (ITF) tests were performed. First, an encapsulation procedure to prepare different specimens including modified and unmodified samples with nano-Zycosil was done. In the following, morphology of the nano-Zycosil-modified capsules and aggregates were particularly evaluated. Considering the morphology evaluation and TG analysis diagrams, it was found that most of the capsules resisted the mixing procedure of the asphalt mixture. So, the encapsulation procedure used in this study was a successful technique. In addition, modification with nano-Zycosil as an anti-stripping agent significantly improved the adhesion strength in the matrix of capsules-aggregates-asphalt binder by converting the adhesion type from silanolian to siloxane. Overall, modification of capsules and main aggregates together with nano-Zycosil significantly improved moisture resistance and mechanical performance of asphalt mixture samples
Numerical analysis and thermal fatigue life prediction of solder layer in a SiC-IGBT power module
Get PDFLimited by the mechanical properties of materials, silicon (Si) carbide insulated gate bipolar transistor (IGBT) can no longer meet the requirements of high power and high frequency electronic devices. Silicon carbide (SiC) IGBT, represented by SiC MOSFET, combines the excellent performance of SiC materials and IGBT devices, and becomes an ideal device for high-frequency and high-temperature electronic devices. Even so, the thermal fatigue failure of SiC IGBT, which directly determines its application and promotion, is a problem worthy of attention. In this study, the thermal fatigue behavior of SiC-IGBT under cyclic temperature cycles was investigated by finite element method. The finite element thermomechanical model was established, and stress-strain distribution and creep characteristics of the SnAgCu solder layer were obtained. The thermal fatigue life of the solder was predicted by the creep, shear strain and energy model respectively, and the failure position and factor of failure were discussed
Optimization design based approach for the determination and minimization of the displacement under tensile load in hybrid composite joint
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Composite materials are most often used for lengthier and thin structures susceptible to buckle. The optimization is often carried out taking into consideration the resistance to buckling and tensile loads for minimum displacement i.e maximization of the tensile load for composite assembly joint. It well known that nowadays that composite material in structural mechanics is widely used in many industrial sectors such as in aerospace and aeronautic, automobile, marine industries as well as in and civil engineering. Composite materials are attractive due to their advantages and performance i.e: lighter weights, high resistance to thermal and mechanical loads, resistance to corrosion and wear.
In this paper an investigation is focused on the problem of hybrid assembly joint (bolted –bonded) composite structures. The aim is the optimization of the main influencing parameters.
A bonded assembly has only one advantage which is its lightness; on the other hand bolted assembly has the inconvenient of increasing the weight of the structure and stress concentrators. In practice certain structural designs require the use of hybrid assembly for safety and reliability. The objective of this study is to optimize the influencing factors using both Genetic Algorithm and design of experiments for high mechanical performance of hybrid composite assembly
Mechanical behavior of materials with a compact hexagonal structure obtained by an advanced identification strategy of HCP material, AZ31B-H24
Get PDFThe use of magnesium alloys, in particular AZ31B-H24, represents an increasingly important aspect in the transport field, as well as in the aeronautical industry. In the forming processes of this material, the shapes of the product are obtained by plastic deformation. Therefore, it is important to know the properties of plastic behavior to optimize these shaping processes. The properties of this alloy are strongly influenced by its complex microstructure which can be modified by plastic deformation. For this purpose, in this work an identification strategy is established beginning with the elastoplastic orthotropic law based on the choice of an equivalent stress, a hardening law and a plastic potential. Thus, the anisotropic behavior of the magnesium sheet is modeled using CPB06 criterion with four hardening laws then later compared to Barlat91 criterion. Once the model is validated, it would therefore be useful to study the plastic behavior of AZ31B-H24 from an experimental database
Probabilistic Elastic-plastic Fracture Mechanics Analysis of Propagation of Cracks in Pipes under Internal Pressure
Get PDFThis study presents a three dimensional finite element method analysis of semi-elliptical surface cracks in pipes under internal pressure load. In the elastic–plastic case, estimates of the J-integral are presented for various ratios including crack depth to pipe thickness (a/t) and strain hardening index in the (R-O) Ramberg-Osgood (n). Finally, failure probability is accessed by a statistical analysis for uncertainties in loads and material properties, and structural reliability and crack size. The Monte Carlo method is used to predict the distribution function of the mechanical response. According to the obtained results, we note that the stress variation and the crack size are important factors influencing on the distribution function of (J/Je)
Prediction of mechanical behavior of friction stir welded joints of AA3003 aluminum alloy
Get PDFFriction stir welding (FSW) is an extremely complex process because it depends on the intrinsic and extrinsic factors of the material under consideration. The purpose of the present work is to formulate a set of recommendations concerning the choice of the different factors that are likely to influence the quality of the FSW joint and to find a mathematical model that allows predicting the mechanical behavior of the junction. An experimental design was therefore used to highlight the effect of the welding parameters on the behavior of the aluminum alloy FS-Welded joint. The most influential parameters were shown to be in the order of rotational speed, feed rate and tool tilt angle. The study of the interactions between these different parameters made it possible to establish a number of combinations of the different factors for the purpose of achieving the quality optimization of the FSW joint by obtaining a tensile strength of the weld joint equal to of that of the base metal
Numerical analysis of underground tunnels subjected to surface blast loads
Get PDFThe increased terrorist attacks on important public structures and utilities have raised the vital necessity for the investigation of performance of structures under blast loads to improve the design and enhance the behavior of structures subjected to such threats. In this study, 3-D finite element analysis is used to study the effect of surface explosions on the response of RC bored tunnels. The soil behavior is modelled using Drucker-Prager Cap model. Two types of soil are investigated, and the blast load is considered through various weights of TNT explosive charges at heights of 0.50 m and 1.0 m from ground surface. To study the effect of horizontal standoff distance, six different horizontal distances are considered. The results show that the soil type has a significance effect on tunnel response due to surface blasts. Also the weight and the location of charge have a great effect on the safety of the tunnel. Finally, a parametric study is established to define the borders of the restricted area around the tunnel location to be safe
The Effect of corrosion on the quality repair of the aluminum alloy A 5083 H11 by bonded composites
No full textIn this paper, the effect of corrosion on the performance of the bonded composite patch repair in aluminum alloy A5083 marine structure was investigated using three dimensional finite element methods. To this end, two patches made in carbon/epoxy and boron/epoxy, bonded on corroded plates with and without crack, were tested under different applied loads. The effect of both corrosion and cracked materials on the damage of the adhesive FM73, was also highlighted. The obtained results show that, the corrosion has a significant effect on the quality repair performance. Indeed, it is proved that, the rate of damage increases with the increase of the applied load, and is more significant in the case of plates cracked and repaired by carbon/epoxy patch. Hence, the best performances were obtained using boron/epoxy patche
Low cycle fatigue damage model and sensitivity analysis of fatigue crack initiation by finite element approach
Get PDFTo meet the design requirements, different types of defects are often machined on the surface of fatigue components. Local stress concentration formed at the notch accelerate the initiation of fatigue crack, therefore greatly shorten the service lives of such components. Based on the theory of continuous damage mechanics and the principle of irreversible thermodynamics, the damage evolution model of low cycle fatigue is investigated. By programming the damage evolution model as UMAT subroutine and coupling it to ABAQUS, the fatigue damage and crack initiation life of notched P92 steel samples under specific loads are simulated, and the crack initiation location is determined. Furthermore, the damage evolution and crack initiation sensitivity of notch morphology are considered. The results show that the crack initiation occurs easily in the notch root where the damage is greatest and the plastic strain accumulates fastest under cyclic loading. The fatigue damage accumulates slowly at the initial stage, but the damage accumulates rapidly after the cumulative damage reaches a critical value. The fatigue damage evolution and fatigue initiation life are very sensitive to the notch morphology parameters. The notch morphology need to be carefully analyzed, to improve the fatigue life of the notched samples