Materials Testing Volume 53 Issue 6

Materials Testing

Volume 53 Issue 6

Contents
Journal Overview

Fatigue Criterion Based on the Novoshilov Criterion for Non-proportional Loadings*

Dariusz Skibicki May 28, 2013

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Abstract

In the present paper the fatigue limit has been calculated under non-proportional loads, proposing a modification of the Huber-von Mises-Hencky criterion, i. e. the Novoshilov interpretation of that criterion was applied. As an effective amplitude, the maximum value of shear stress in the non-proportional load cycle was assumed. There has also been proposed the weight function showing preference of the directions of easy slip in the network A2. Subsequently, verification calculations were performed for respective literature data. The data included experimental fatigue limits reported under biaxial loads which are sinusoidally variable from the phase shift. The present results are compared with the Huber-von Mises-Hencky criterion. The analysis showed that the proposed solutions demonstrate greater accuracy, especially under loadings with a high degree of non-proportional loads.

The Dynamics of Loading and Growth of Fatigue Cracks in the Proximity to Rolling Contact of Elements with Defects on Their Surface*

Mariusz Pietrzyk, Stanisław Bogdański May 28, 2013

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Abstract

This paper highlights the analysis of the development of fatigue cracks under loading in the region of rolling contact. A surface defect is taken as an irregularity of a convex circular profile on an otherwise regular contact track, on which a rolling element is moving. 2D numerical models with different lengths of cracks were analysed. The results provided an estimation of the influence of the irregularity height and the length of a crack on the stress intensity factors (SIF) at the crack tip, and, as a consequence, on the crack growth rate and direction. A simplified model of contact was used in which the rolling element was replaced by the distribution of displacements equivalent to its interaction. It was assumed that an element in a contact pair having a large mass and moving with a high velocity would not deviate from its initial path while rolling over the irregularity on the track. This allowed the dynamic contact interaction and corresponding crack tip loading to be estimated, despite the use of a quasi—static model for the analyses.

Modelling of Stresses in Welded Joints Under Consideration of Plastic Strains in Fatigue Life Calculations*

Łukasz Blacha, Aleksander Karolczuk, Tadeusz Łagoda May 28, 2013

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Abstract

Welded joints submitted to variable loadings are, by their nature, experiencing a stress concentration resulting from the presence of a complex notch effect relating to geometrical and structural features of the joint. In the finite element method, modelling of the weld toe as a sharp notch reveals a non-linear relation of stresses dependent on the mesh density. In this paper, an approach for determination of the notch radius in a welded part was proposed, based on the application of finite element calculations with a non-linear elastic-plastic body model under employment of the linear hardening rule. The derived stresses are used in calculations of fatigue life, carried out according to algorithms provided for structural elements without the presence of welds.

Fatigue Energy Dissipation in Trabecular Bone Samples with Stepwise-Increasing Amplitude Loading*

Tomasz Topoliński, Artur Cichański, Adam Mazurkiewicz, Krzysztof Nowicki May 28, 2013

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Abstract

The research method proposed in the paper assumes multi-level loads of trabecular bone, which are similar to the real ones and demonstrate a step-wise amplitude increase. Throughout the study, such loadings were applied to bone structures sampled from 61 donors. The samples were obtained after hip arthroplasty from the neck fragment of femur heads. All the samples were scanned with a desktop microtomographer. The fatigue damage of the sample structures throughout the experiments was seen in changes in the form of the hysteresis loop recorded in the stress-strain system. The dissipation energy, which is calculated based on the hysteresis loop, is present in the fatigue life function. A three-stage sample fatigue damage pattern was demonstrated. The sum of the dissipation energies was calculated for all the hysteresis loops, and thus we obtain the accumulated dissipation energy, which is referred to as the total fatigue life for all the samples. The calculation results were determined to have an exponential-like curve and reported a high value of the coefficient of determinacy. The accumulated dissipation energy is also related to the value of the compressive stress levels applied. Referring the calculated results of the accumulated energy to the structure index BV/TV, we identified the existence of a strong relationship between the quantities.

Damage Identification in Strongly Loaded Carbon-Reinforced Composite Using the Electric Resistance Change Procedure*

Jacek Gadomski, Paweł Pyrzanowski May 28, 2013

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Abstract

Composite materials are often used as primary structures in important devices, like transport facilities. However, prediction of their work and damage propagation is not easy. Operating of the structure causes delaminations and fibers cracking which are difficult to detect by visual investigation. The paper presents an experiment in which an electrical resistance change method was used for investigating damage in strongly loaded carbon-fiber reinforced plastic composites, where the conducting carbon fiber was used as a sensor for defect detection. The method is shown by which the electric potential difference was measured at the carbon/epoxy composite beam type specimen exposed to the action of pure bending moment.

Mechanical Properties and Corrosion Behaviour of MIG Welded 5083 Aluminium Alloy

Hülya Durmuş May 28, 2013

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Abstract

For this study 5083 Aluminium alloy plates, as used in automobiles and watercraft, were experimentally MIG welded. The plates were joined with different wires and at various currents. The effects of welding with different parameters on the mechanical and corrosion properties were investigated. The corrosion behaviour of the MIG welded 5083 Aluminium base material was also investigated. The effects of the chemical composition of the filler material on the mechanical properties were examined by metallographic inspection and tensile testing. By EDS and XRD analyses of specimens it turned out that different structures in the weld metal (Cu 3 Si) affect its mechanical properties. The mechanical properties of the specimens welded with 5356 filler metal were found as quite well improved as compared to those specimens welded with 4043 and 5183 filler material. The results of the metallographic analysis, and mechanical and corrosion tests exhibited that the 5356 filler material was most suitable for the 5083 Al alloy base material.

Kenaf Performance in PP/EVA/Clay Biocomposite

Siti Kamaruddin, Khalina Abdan, Aidy Ali, Bernard Maringgal, Siti Jamaliah, Wan Md Zin Md Yunus May 28, 2013

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Abstract

In this study, laminated Kenaf nanocomposites made from Kenaf fiber, Polypropylene (PP), organoclay, and Ethylene Vinyl Acetate (EVA) are fabricated with the combination of hand-layup and compression moulding technique. The effect of Kenaf fiber on properties of PP/EVA/clay biocomposite is investigated. The comparisons are made between the composite reinforced with Kenaf fiber and the composite without Kenaf fiber in terms of mechanical and thermal conductivity properties. Dynamic mechanical analysis (DMA) is carried out to examine the thermal mechanical properties of biocomposite samples. The surface fracture of laminated Kenaf nanocomposites is investigated by scanning electron microscopy (SEM). Results verify that Kenaf fibers have great potential to be used as an alternative to inorganic mineral-based reinforcing fibers.

Topology Optimization for a Micro/Nano Compliant Grip and Move with Parallel Movement Tips Using Multi-Objective Compliance

Mahmoud Helal, Lining Sun, Liguo Chen, Weibin Rong Harbin May 28, 2013

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Abstract

The past few years have witnessed an increasing maturity of the micro- and nano-electro-mechanical systems (Mems/Nems) industry and a rapid introduction of new products addressing applications ranging from biochemical analysis to fiber-optic telecommunications. The assembly of micro-devices involves handling of parts that are extremely very small. A microgripper compliant mechanism is one of the key elements in micro-robotics and micro-assembly technologies for handling and manipulating micro- objects without damage. This paper presents the design of compliant grip and move manipulators with parallel movement tips. The integration of both, gripping and moving manipulators, with parallel movement tips is accomplished by the use of compliant mechanisms, which generate paths that are symmetric. These mechanisms can grip an object and convey it from one point to another with parallel movement. The structural topology optimization approach is applied in order to find the optimal material distribution in the proposed domain for compliant mechanisms. The objective of the optimization problem is to maximize the structural stiffness within the limit of prescribed design volume. A two-dimensional finite element analysis model using Ansys is constructed for the proposed design domain. Three optimal configurations of two-dimensional compliant mechanism, which can realize a micro grip and move with parallel movement tips for a wide range of micro- and nano-objects, are demonstrated.

Modelling and Experimental Study of Mechanical Behaviour of Walls Produced by Different Knitting

Mehmet Kamanli, Mahmut Sami Donduren, Mustafa Tolga Cogurcu, Mustafa Altin May 28, 2013

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Abstract

This study aims to investigate the shear behavior and resistance of brick walls produced by various knitting types. For this purpose, 15 samples were produced using Holland knitting, block knitting, cross knitting, lock knitting, and plain knitting. The samples were forced in experiments to collapse and in the non-linear region, the changes in the samples related with shear forces and shear rigidity of the wall sections were determined. In the performed experimental study, the standard sliding resistance test technique for the masonry wall samples has been determined as recommended in ASTM Standard 1391-81. The numerical modeling was carried out by the finite elements method with the program package Ansys, taking into account the local mechanical parameters of bricks and mortar. The behavior of the experimental samples and the cracks occurred during the experiments were analyzed and shear stress graphs and load-displacement graphs were derived. The modeling with the Ansys program was compared with the experimental results and the most appropriate wall knitting type could be proposed.

Vorschau

May 28, 2013

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About this journal

Materials Testing is a SCI-listed English language journal dealing with all aspects of material and component testing with a special focus on transfer between laboratory research into industrial application. The journal provides first-hand information on non-destructive, destructive, optical, physical and chemical test procedures. It contains exclusive articles which are peer-reviewed applying respectively high international quality criterions.
All articles are subject to thorough, independent peer review.

Editing Associations: DGZfP, DVM and VDI Materials Engineering.