Stress intensity factor and plastic zone of auxetic materials: a fracture mechanics approach to a chiral structure having negative poissons ratio

This article summarizes the method of analytical formulation and computational approach of stress intensity factor and plastic zone calculation for auxetic materials, which have negative Poissons ratio. A chiral structure-based material is selected as an object of the study due to its popularity. The stress intensity factor is used in combination with the von Mises yielding condition to estimate the plastic zones shape and size. The results show that macroscopically the shape of the plastic zone for auxetic material is the same with that of ordinary materials. However, its size is smaller due to the reduction in its Youngs modulus from the solid material of which the auxetic material is made. Microscopically, an auxetic material has its plastic zone shape that is unique to its microstructure. Homogenization theory was convenient to use to bridge between the microscopic and macroscopic models

The effect of silicon composition on corrosion behavior of aluminum die-cast

ADC 12, ADC 1 and HT 1 die cast aluminums mainly differ in their composition of silicon. The shape of silicon particles had made a difference in term of improving strength, elasticity, corrosion resistance and promotes large grain sizes which causes increasing magnetic permeability, and presumably corrosion. In this research, the effect of the silicon composition on the corrosion behavior was investigated. Through immersion corrosion test for the period of 28 days, the corrosion behavior of die-cast ADC 1, ADC 12 and HT 1 aluminum alloys had been determined. Further assessment of micro-structural examination was conducted with the morphology and the location of the pits. The experimental results showed that the corrosion rate was the highest in the sample with the least of silicon content, which is ADC 12. Micro-structural observation with areal analysis revealed that the pitting morphology at the eutectic silicon and intermetallic phases being dependent upon the interface with the aluminum phase. More interface area promotes more pittings, since the pitting corrosion are more active at the interfaces

Influence of ferrite fraction within martensite matrix on fatigue crack propagation: an experimental verification with dual phase steel

The influence of a ferrite areal fraction within a martensite matrix on fatigue crack propagation is studied experimentally. The variation of the areal fraction is achieved by means of intercritical thermal treatment, which specifically aims at optimizing the resistance to fatigue loading. Within the intercritical annealing temperature range, the areal fraction of ferrite increases with decreasing soaking temperature. Furthermore, the experiment also reveals that the highest fatigue strength was achieved when the ferrite areal fraction was approximately 65%, which in this particular test, corresponds to 748 degrees C. It is concluded that appropriate thermal treatment can contribute to a significant improvement of fatigue properties and strength, which was also verified by computational modeling. (c) 2012 Elsevier B.V. All rights reserved

Application of J-integral concept on blister coating problem

This is analytical and computational approaches to coating blistering problem using the concept of J-integral. The result is compared with other available models, which are typically derived based on energy method or its derivatives. The result shows that J-integral has the big potential to be used for coating adhesion parameter similar with stress intensity factor and strain energy density. Being developed in the non-linear area, the J-integral has wider application coverage than the existing formulas developed by using linear elastic mechanics

Exploring the potential use of adhesion strength for coating analysis

This paper discusses the possibility of the potential use of adhesion strength for coat ing analysis. Most of the steel structures used in industrial and non-industrial applications are exposed to outdoors weathering conditions. Organic coating typically protects them from corrosion. The maintenance actions can be done efficiently only if there is sufficient information on the accurate condition of it. Therefore, the deterioration of the coating system and its lifetime has to be assessed accurately. Adhesion strength has the potential to be used as a parameter for evaluation. This paper explores the development of these parameters mainly based on fracture mechanics

Stress corrosion cracking of steel and aluminum in sodium hydroxide: field failure and laboratory test

Through an investigation of the field failure analysis and laboratory experiment, a study on (stress corrosion cracking) SCC behavior of steel and aluminum was performed. All samples were extracted from known operating conditions from the field failures. Similar but accelerated laboratory test was subsequently conducted in such a way as to mimic the field failures. The crack depth and behavior of the SCC were then analyzed after the laboratory test and the mechanism of stress corrosion cracking was studied. The results show that for the same given stress relative to ultimate tensile strength, the susceptibility to SCC is greatly influenced by heat treatment. Furthermore, it was also concluded that when expressed relative to the (ultimate tensile strength) UTS, aluminum has similar level of SCC susceptibility to that of steel, although with respect to the same absolute value of applied stress, aluminum is more susceptible to SCC in sodium hydroxide environment than steel

Re-visiting the 'rule of mixture' used in materials with multiple constituting phases: a technical note on morphological considerations in austenite case study

This is a technical note highlighting a method on how to perform averaging the elastic properties. The drawback of the traditional rule of mixture (ROM) is briefly discussed. The technique considers the effect of morphology based on classical continuum mechanics, taking the advantages of fracture mechanics. As an example, a model that simulates the possible configuration of constituting phases commonly found in austenite microstructure is chosen. The result is compared with traditional ROM. It is found that although similar, the result is better due to the stress amplification that is accommodated in the method, unlike the traditional ROM, which merely considers only the volumetric ratio

Three-dimensional modeling to compute plastic zone in front of crack in compact tension sample of multiphase material

Two-dimensional modeling to compute plastic zone in front of a crack in a compact tension specimen of a multiphase material was published previously. This paper is the continuation of it, using the same concept, but in three dimensions. The heart of this study is to develop a simulation method to predict the effect of microstructural morphology in multiphase steel in three dimensions utilizing commercial software. The object of the model, multiphase of ferrite and martensite, is known to benefit its fatigue performance by its high toughness yet maintains the high tensile properties due to controlled microstructure. Multiphase steel having a microstructure consisting of polygonal ferrite and martensite has received a great deal of attention due to their useful combination of high strength, high work hardening rate, and ductility. From the fracture mechanics point of view, the key to its fatigue performance is the large plastic zone size in front of the crack. In this research, a sub-modeling technique is used, by using three-dimensional modeling of cube with variation of ferrite fraction as local models. The global model, a compact tension specimen, is treated as a homogeneous material. The results show strong correlation and similarity with that of two-dimensional model. The analysis result shows the variation of the plastic zone sizes as the ferrite fraction varies and saturates at about 60% ferrite fraction

Effect of microstructures and material compositions on blister formation

One of the early failures of coating is blister. Here two different coatings were applied on various materials and micro-structures. The formation of the blister, and its micro-structural and material dependencies were evaluated. It is concluded that general organic coating forms more severe blisters than that of the metallic effect coating. General organic coating protects the samples by insulation film while metallic coating protects by acting as galvanic protection. Therefore, the failure modes are also different, namely blister and filiform corrosion. The dependencies on the micro-structures and on material types also follow the insulation film concept and galvanic protection concept

Coating life assessment : the use of adhesion strength in parametric development in coating degradation evaluation

Most of the steel structures used in industrial and non-industrial applications are exposed to outdoors weathering conditions. Organic coating typically protects them from corrosion. The maintenance actions can be done efficiently only if there is sufficient information of the condition. Therefore, the deterioration of the coating system and its lifetime has to be assessed accurately. This paper focuses on the development of parameters based on adhesion strength useful for that purpose. Three parameters are proposed, namely stress intensity factor, strain energy density, and J-integral