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

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

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

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

Mesomechanical aspects of computational modeling for non-homogeneous materials joined by forming

The metal forming and joining industries are constantly evolving to adapt to new materials and alloys and to meet customers’ needs. However, the size of the companies in this segment is typically small. Therefore, the progress of the mesomechanical modeling on non-homogeneous materials is relatively slow. This article aims to contribute to the advancement of such computational idea. The industries and academics alike may benefit the mesomechanical aspects of computational modeling for materials joined by forming using the established theories known in the field of mechanics. It may be used as an introductory for the society of joining by forming. This article reviews the basic concept of the finite element method, the fundamental mechanics and highlights some common problems in joining by forming, namely contact problems, local variations and interfacial cracking. This article aims to disseminate the meso/micro-mechanics approach to the field of joining by forming, which currently is dominated by experimental works and macroscopic modeling. Using the simple approaches discussed in this article, researchers with little or no background in computational mechanics can implement the concepts

Incorporating the morphological difference of corrosion cracks in computational fracture mechanics approach

This paper encourages materials scientists to incorporate computational approach in their research. At the same time it gives a warning on how to use it, especially for stress corrosion cracking (SCC), since any continuum approach is highly dependent upon the shape of the crack. Evaluating the basic morphology of the SCC behavior of steels shows that each microstructure produces unique shape that can be used as a foundation for computational model creation

PENGGUNAAN RADIASI SYNCHROTRON UNTUK PENGUKURAN DAERAH PLASTIS PADA MATERIAL BAJA KARBON

PENGGUNAAN RADIASI SYNCHROTRON UNTUK PENGUKURAN DAERAH PLASTIS PADA MATERIAL BAJA KARBON. Pada penelitian ini perubahan ukuran daerah plastis digunakan untuk verifikasi hasil analisis faktor intensitas tegangan dari retakan lelah yang dilakukan pada material yang memiliki tegungan sisa tarik. Daerah plastis vertikal digunakan untuk menyelidiki jejak faktor intensitas tegangan maksimum di dalam dan di luar daerah yang memiliki tegangan sisa tarik. Daerah plastis vertikal dideteksi dengan metoda line broadening dengan menggunakan radiasi synchrotron dengan ukuran spot 50 x 50 μm. Hasil pengukuran daerah plastis ini kemudian dibandingkan dengan hasil estimasi analitik. Hasil estimasi analitik ini didapatkan dengan imenjumlahkan faktor intensitas tegangan kerja maksimum dan faktor intensitas tegangan sisa yang dihitung dengan metoda weight function. Ukuran daerah plastis tertetak antara hasil analisis Rice dan Irwin. Juga dibandingkan dengan perhitungan menggunakan konstanta yang diperoleh dengan metoda micro hardness dan metoda etsa. Disimpulkan bahwa line broadening dari radiasi syncjrotron dapat digunakan untuk mengukur daerah plastis yang terbentuk selama proses peretakan. Total maximum faktor intensitas tegangan adalah jumlah dari faktor intensitas tegangan kerja maksimum dan faktor intensitas tegangan sisa sesuai dengan prinsip superposisi

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

How to compute plastic zones of heterogeneous materials : a simple approach using classical continuum and fracture mechanics

This is a short technical paper on how to use classical continuum and fracture mechanics to calculate the plastic zones caused by cracks on heterogeneous or composite materials. As an example, a sample consisting of an α-phase and β-phase is used. A crack is introduced to the sample, and stress is then applied. The plastic zone in front of the crack resulting from the applied stress is then calculated using commercial software. The concept uses two-level modeling: a global model using homogenized stiffness from a unit cell of heterogeneous material and a local model for the α-phase and β-phase. While this paper is written for general purposes, a concrete example using ferrite and martensite is also presented along with the experimental data. General agreement between the model and the experiment is observed. This method eliminates the need for a cumbersome analytical approach