The post-buckling behavior of the composite plates with embedded shape memory alloy subjected to combined loading using finite element method

Thin composite structures that are used in aerospace applications can be subjected to buckling failure due to combined mechanical and thermal loadings. This paper presents the work on the thermal post-buckling improvement of composite plates previously subjected to mechanical loading. Pre-strained shape memory alloy wires were embedded within laminated composite plate so that the recovery stress that can improve strain energy of the plate can be induced when the wires were heated. A geometric non-linear finite element formulation of the shape memory alloy composite plate and its source codes were developed. The formulation is based on total strain for the case of mechanical loading and incremental strain for the case of thermal loading. Using the codes, post-buckling paths were determined for quasi-isotropic and anti-symmetric cross-ply composite plates. It was found that by embedding shape memory alloy wires within composite plates, thermal post-buckling paths can be improved significantly even after the degradation of the thermal buckling resistance of composite plates due to the application of the mechanical loading

Simulation of low velocity impact on composite hemispherical shell

Impact simulation with finite element analysis is an appropriate manner to reduce the cost and time taken to carry out an experimental testing on a component. In this study, the impact behavior of the composite hemispherical shell induced by low velocity impact is simulated in ABAQUS software with finite element method. To predict the responses of Kevlar fabric/polyester, glass fabric/polyester and carbon fabric/polyester in the form of a hemisphere, once as one layer and then as a three-layered composite under applied force by an anvil. The sequences of layers are changed, to investigate and compare the occurred alternations in the amount of energy absorption, impact force and specific energy absorption (SEA). The comparison of results showed that the highest and the lowest quantity of energy absorption and SEA belong to Carbon/Glass/Kevlar (CGK) and Kevlar/Carbon/Glass (KCG) respectively

A Review Paper on Comparison of Numerical Techniques for Finding Approximate Solutions to Boundary Value Problems on Post-Buckling in Functionally Graded Materials

The use of finite element models as research tools in biomechanics and orthopedics grew exponentially over the last two decades. However, the attention to mesh quality, model validation and appropriate energy balance methods and the reporting of these metrics has not kept pace with the general use of finite element modeling. Therefore, the purpose of this review was to develop the nonlinear filter and thermal buckling of an FGM panel under the combined effect of elevated temperature conditions and aerodynamic loading is investigated using a finite element model based on the thin plate theory and von Karman strain-displacement relations to account for moderately large deflection. It is found that the temperature increase has an adverse effect on the FGM panel flutter characteristics through decreasing the critical dynamic pressure. Decreasing the volume fraction enhances flutter characteristics, but this is limited by the structural integrity aspect. Structural finite element analysis has been employed to determine the FGM panel's adaptive response while under the influence of a uniaxial compressive load in excess of its critical buckling value. By increasing the applications of using composite materials inside aviation stages, it is visualized that the versatile FGM plate setup will broaden the operational execution over traditional materials and structures, especially when the structure is presented to a raised temperature. The vicinity of air motion facilitating stream brings about delaying the locking temperature and in stifling under loads, while the temperature build gives route for higher thermal-cycle abundance

Modelling of residual stress relaxation: a review

Compressive residual stress, induced by mechanical surface treatment, may relax during component operation life, due to thermal or mechanical mechanism. Fatigue life prediction for the components which have residual stress will be misled and inaccurately predicted the phenomenon of residual stress relaxation is not considered. Despite putting an effort on incorporating the residual stress relaxation, the issues remain concerned with the technical challenge of measuring and quantifying the magnitude of residual stress relaxation as well as redistribution during the loading cycling itself. In this paper, the residual stress relaxation and its models were reviewed and discussed to picture the best knowledge related to this topic, i.e. whether relaxation is a cause or an effect

Residual stress relaxation and surface hardness of a 2024-t351 aluminium alloy

For design it is generally important to consider the residual stress relaxation. In the study for this contribution, 2024 T351 Aluminium alloy specimens were shot peened at three different shot peening intensities, followed by fatigue tests for two loads. Fatigue tests were divided into two stages. The residual stresses and micro-hardness were measured at initial and after each cyclic load for the three shot peening intensities and the two aforementioned sets of loads. The results showed that the residual stresses and micro-hardness of the specimens were decreased. Moreover, the relaxation depended on the fatigue load amplitude. Residual stress relaxation reached 54% of the initial residual stress while the micro-hardness relaxation reached 39% of the initial micro-hardness. Most of the residual stress relaxation occurred during the first cycle. The relaxation of the initial residual stress is severe when there is low shot peening intensity and high applied load, and the reduction of the micro-hardness is depending on the residual stress relaxation

Modelling of residual stress relaxation : a review

Compressive residual stress, induced by mechanical surface treatment, may relax during component operation life, due to thermal or mechanical mechanism. Fatigue life prediction for the components which have residual stress will be misled and inaccurately predicted the phenomenon of residual stress relaxation is not considered. Despite putting an effort on incorporating the residual stress relaxation, the issues remain concerned with the technical challenge of measuring and quantifying the magnitude of residual stress relaxation as well as redistribution during the loading cycling itself. In this paper, the residual stress relaxation and its models were reviewed and discussed to picture the best knowledge related to this topic, i.e. whether relaxation is a cause or an effect

Micro-hardness and residual stress relaxation of 2024 T351 aluminum alloy

The residual stress relaxation can be divided into two stages: The first cycle relaxation and the following cycles. In both stages, residual stress relaxed considerably from the initial state. The aim of this study is to investigate the residual stress relaxation and microhardness reduction after first and second cyclic load. A 2024 T351 aluminum alloy specimens were shot peened into three shot peening intensities. The fatigue test for first and second cyclic loads of two loads 15.5 kN and 30 kN was performed. The initial residual stress and residual stress after the first and second cycle stress was measured for the three shot peening intensities using X-ray diffraction. Microhardness test was performed for each specimen. The results showed that the residual stress relaxation for first cycle was reached more than 40% of the initial residual stress and it depends on the load amplitude, and microhardness decreased for the first cycle reached 22% and also it depended on load amplitude

Alternative numerical validation methodology for short-term development projects

Virtual prototyping has been increasingly taking over the process of sole physical tests. Companies are reporting up to 80% reduction in errors when using virtual tests through the design process. Conventional numerical validation methodology however, is not as beneficial for short-term projects because any new numerical scenario has to be validated before being used. Although during the conceptual stage, relative values can be sufficient. The alternative methodology proposed also uses realistic loads. It comprise applying these loads on a functioning structure to verify them. The modified version of the structure is then relatively validated by being tested under these verified loads. Thus, bypassing the physical tests requirement. Aerodynamic loads are acquired from simulating the Gulfstream IV-SP forward fuselage during climbing, cruising and landing. Mechanical loads are acquired from estimating structural weight and impact load during landing. In total, three finite element models were created. Autodesk softwares were used to perform CFD and FEA. Only greater loads were applied during FEA. Results simplified neglected cruising data for having lowest values. Comparing estimated weights of functional and modified structures showed a possible 15% weight savings. While the FEA results showed a promising 45% less inquired stress within the modified structure

Effects of different cross-section shapes on bending and weight of harvesting pole by using finite element analysis

Harvesting pole is a main requirement in harvesting activity that involves tall trees. A long pole always has problems with bending and weight. Study on the effect of cross-section shapes on bending and weight may give some information about the best design for harvesting pole. Laboratory testing is expensive and time consuming. Finite element analysis using computer software is the best method and cost less. A total of six designs of pole cross-section were tested using Pro-Mechanica software for obtaining their bending/deflection. The six shapes are circular, hexagon, octagon, decagon, icosagon and ellipse. A total of five testings were implemented, that consist of combination of three pole conditions, loaded/unloaded, end/middle constrained and same/different weight. The analyses results show that the circular cross-section shape is the strongest shape to resist bending. Ellipse cross-section shape has different value of bending depends on the orientation. Final evaluation shows circular and icosagon were the best cross-section of harvesting pole

Extraction and preparation of bamboo fibre-reinforced composites

Natural plant fibre composites have been developed for the production of a variety of industrial products, with benefits including biodegradability and environmental protection. Bamboo fibre materials have attracted broad attention as reinforcement polymer composites due to their environmental sustainability, mechanical properties, and recyclability, and they can be compared with glass fibres. This review classifies and describes the various procedures that have been developed to extract fibres from raw bamboo culm. There are three main types of procedures: mechanical, chemical and combined mechanical and chemical extraction. Composite preparation from extracted bamboo fibres and various thermal analysis methods are also classified and analysed. Many parameters affect the mechanical properties and composite characteristics of bamboo fibres and bamboo composites, including fibre extraction methods, fibre length, fibre size, resin application, temperature, moisture content and composite preparation techniques. Mechanical extraction methods are more eco-friendly than chemical methods, and steam explosion and chemical methods significantly affect the microstructure of bamboo fibres. The development of bamboo fibre-reinforced composites and interfacial adhesion fabrication techniques must consider the type of matrix, the microstructure of bamboo and fibre extraction methods