Amir H. Mahmoudi

Bu-Ali Sina University, Hamedan, Iran · Mechanical Engineering Department

To maintain the structural integrity in additively manufactured samples, it is important to study the induced residual stresses which are widely ignored. Powder bed fusion (PBF) is a type of additive manufacturing process in which the metal powder is added to a substrate, step by step. Scanning parameters including layer thickness, overlap percenta...

Residual stresses can have detrimental effect on the life cycle of engineering components. They can also alter the accuracy of the fatigue life prediction models. Therefore, it is important to measure such stresses with accuracy. One of the issues with the destructive and semi-destructive methods of measuring residual stresses is the damage they ca...

The simultaneous determination of mechanical properties and residual stresses using the instrumented indentation technique is more challenging when the anisotropic behaviour of a material is considered. If ignored, it may lead to inaccurate estimation of residual stresses and mechanical properties of materials. In this paper, the existence of in-pl...

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Water jet peening is a surface modification technique which can introduce compressive residual stresses beneath the surface of the engineering components. In this paper, the effects of water jet peening process, in the absence of abrasive materials on residual stresses, surface roughness, and fatigue life of the aluminium alloy 7020 samples were nu...

In some industrial applications, welding is the only alternative to join different parts. However, the major problem in welded structures is the tensile residual stresses that are inevitably produced during welding process. Surface tensile stresses can threaten the performance of the weldments as they act as an accelerant in fatigue crack initiatio...

In shell and tube heat exchangers, deep cracks can occur in tube-to-tubesheet welding and repairing such cracks is an impossible task which makes these tubes totally out of service. To preserve the thermal and mechanical integrity of heat exchanger, a series of rods is passed through these tubes and then are welded to tubesheets from both ends. Due...

A residual stress analysis is indispensable to anticipate engineering structure loading conditions. For this purpose, there are various methods, including indentation technique, a non-destructive test, which also enables us to measure material properties as well. Numerous studies have been conducted until now, but it is yet to be completed. Study o...

In a shell and tube heat exchanger, the failure of tube-to-tubesheet welds results in high-pressure water jet which erodes the refractory in front of the tubesheet. Finite element method was employed to simulate the welding process and post weld heat treatment (PWHT) to find the factors affecting the failure in tube-to-tubesheet weldments. Residual...

The main function of a fired heater in a petrochemical site is to produce supersaturated steam. Due to extremely difficult working conditions and high temperatures, there is a very high probability of failures in different parts of a fired heater. In the fired heater under study, tube guides are frequently damaged due to malfunctions and fractures...

A proper knowledge of the mechanical properties and residual stresses of materials has a significant role in the prediction of engineering failures. Indentation is a simple, nondestructive test that is capable of estimating both residual stresses and mechanical properties. In frequent studies, the response of materials during the indentation proces...

To determine mechanical properties, instrumented indentation is a non-destructive one where traditional methods (such as tensile test) are not accessible. However, there are several serious challenges when trying to correctly use this technique. Here, a method to predict the steel stress-strain uniaxial curve is presented accompanied by an experime...

Residual stresses measurement techniques are constantly modified and progressed. There have been many residual stresses measurement methods developed and practiced by researchers. Slitting method is one of the destructive techniques that can measure residual stresses deep within the components. However, the conventional slitting method can only mea...

It is occasionally important or even inevitable to measure residual stresses without harming engineering components. Spherical indentation can be categorized as a nondestructive method to measure residual stresses, as it causes very little damage to the surface of the sample. Furthermore, it is cheap and quick. Spherical indentation has gained the...

Shot peening is one of the most effective surface treatments for improving the fatigue strength of machine elements. In this paper, a new finite element-based model to predict the effect of coverage on the surface state is proposed and critically discussed. By this model, the effects of Rayleigh damping, mesh size, and target dimensions on residual...

Surface modification techniques have received much attention among the researchers around the world. Yet, finding the best way to enhance the surface properties remains one of the challenges in engineering. Most of the fatigue cracks begins from the surface of the engineering components. A well-known technique to delay the crack initiation or slow...

Mechanical properties of HSLA-100 steel at room and subzero temperatures of -40°C, -80°C and -196°C were investigated in this work. Dry ice and liquid nitrogen were used to reach the low temperatures. Also, the material response to different strain rates was studied. Quasi-static tensile test rig and tensile Hopkinson split bar were employed to car...

This paper presents an analytical model to predict the residual stress distribution induced by Shot peening. The analytical approach is based on the work of Shen and Atluri [S. Shen, S.N. Atluri, An analytical model for shot-peening induced residual stresses, Comput. Mater. Con. 4 (2006) 75-85] with some modifications. The modifications are related...

Shot peening is one of the most effective surface strengthening treatment technologies in which compressive residual stresses are induced beneath the specimen surface. Effects of various factors on the distribution of residual stress profile induced by shot peening have been investigated by many researchers. However, initial residual stresses are o...

Experimental methods to determine residual stresses are mainly divided into destructive and non-destructive categories. Contour method is a destructive technique that offers a two dimensional map of normal component of residual stresses. The conventional contour method creates a map of residual stress component by cutting the specimen in half and m...

Spherical indentation is one of the non-destructive techniques that has gained great interest among researchers in recent years. Spherical indentation is inexpensive and quick and can provide a fairly accurate estimation of in-plane residual stresses. This method has typically been used to characterize material properties. However, the application...

An exact knowledge of residual stresses that exist within the engineering components is essential to maintain the structural integrity. All mechanical strain relief (MSR) techniques to measure residual stresses rely on removing a section of material that contains residual stresses. Therefore, these techniques are destructive as the integrity of the...

Residual stresses have become an important player in the field of structural integrity for many years. Exact knowledge of residual stress distributions is essential in designing the engineering components as unexpected failures are inevitable wherever such stresses are ignored. There are many residual stresses measurement techniques including destr...

In the present study an Artificial Neural Network (ANN) approach is proposed for residual stresses estimation in engineering components using indentation technique. First of all, load-penetration curves of indentation tests for tensile and compressive residual stresses are studied using Finite Element Method (FEM) for materials with different yield...

Residual Stress measurement has gained interests among researchers for many years. Slitting method is one of the destructive techniques that relies on the introduction of an increasing cut to a part containing residual stresses. Similar to all other mechanical strain relief techniques, slitting suffers from the level of plasticity occurs within the...

Mechanical strain relief techniques for estimating the magnitude of residual stress work by measuring strains or displacements when part of the component is machined away. The underlying assumption is that such strain or displacement changes result from elastic unloading. Unfortunately, in components containing high levels of residual stress, elast...

Precise understanding of concrete target behavior when subjected to high velocity impact of an eroding projectile involves analysis and studying the plastic flow field around the penetrating projectile. In this paper, the flow field around an eroding projectile is reviewed and the main equations of it are presented. Assuming viscoplastic behavior a...

The subject of this study is to investigate the effect of repair on the fatigue life of tubular joints. Six cracked specimens previously subjected to fatigue loading underwent weld repair. Two of these specimens were shot peened before primary fatigue loading. It is shown that repair for the original specimens increases the fatigue life by roughly...

The fatigue life and also the welding residual stress of the welded tubular X-joints are investigated experimentally. Furthermore, some joints are shot peened and the effect of shot peening on fatigue life of these joints is explored. The results of experiment show that the fatigue life of shot peened tubular joint is about twice of the original tu...

An offshore structure is exposed to environmental loading and cyclic stress variations throughout its life. This would result in the possibility of fatigue cracking in its members. Cracks in these structures usually initiate around welded areas, then grow progressively from the heat-affected zone to base metal through the thickness of the tubular m...

Material characteristics such as Young modulus, yield, and ultimate stresses are often considered as fundamental material parameters. Determination of material characteristics using the instrumented indentation test has gained interest among many researchers. The output of a spherical indentation test is usually the load-penetration (P-h) curve whi...

Residual Stresses show significant effects on the engineering structures which can be led to change of the design parameters. To study the influence of the residual stresses on the structural integrity, a reliable source to generate such stresses is of importance. It is even more critical when production of repeatable residual stress fields is requ...

Residual stresses have an important role in many failure processes such as fatigue, fracture, buckling and crack propagation. Residual stress measurement techniques are categorized as destructive, semi-destructive and non-destructive techniques. Contour Method is a destructive technique that can measure two dimensional residual stresses. In this te...

Determination of material characteristics using the instrumented indentation test has gained interests among many researchers. The output of a spherical indentation test is usually the load-penetration (P-h) curve. To achieve this goal, the elastic deformation of sphere must be eliminated from the penetration. To determine three parameters of the L...

Chaboche model can be used to predict the ratcheting phenomenon. The parameter determination of this model to achieve an accurate ratcheting prediction is of great importance. Therefore, the application of an optimization procedure can improve the prediction of this model. In this research, Chaboche kinematic hardening model with five decomposed ru...

Residual stress measurement of shrink-fitted assemblies was achieved through finite element simulations and experiments using the deep hole drilling technique. Shrink-fitted assemblies using stainless steel and cast iron were manufactured and residual stresses measured using a combination of deep hole and centre hole drilling. The results from the...

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Mechanical strain relief covers a class of techniques for measuring residual stress in engineering components. These techniques work by measuring strains or displacements when part of the component is machined away. The assumption is that such strain or displacement changes result from elastic unloading; however, in components containing high magni...

Autofrettage is a well-known method to increase the load carrying capacity of the pressure vessels. The autofrettage outcomes can be contrary when the imperfections or material discontinuities are on the outer surface. In this study, the influences of the external inclined cracks on the fracture parameters in autofrettaged cylinders were studied. T...

Chaboche model is a powerful tool to evaluate the cyclic behavior under different loading conditions using kinematic hardening theory. It can also predict the ratcheting phenomenon. To predict the ratcheting, it is required to determine the material parameters under strain control conditions. Although, these parameters can model the hysteresis loop...

A series of experiments conducted on two steels, A533B and A508, are summarised. Tests were conducted to explore the influence of different room temperature pre-loading cycles on subsequent low temperature (−150°C and −170°C) cleavage fracture. In all cases the low temperature fracture toughness was modified, with tensile pre-loading increasing the...

Accurate evaluation of residual stress is essential if is to be taken into account in structural integrity assessments. For thick components, many non-destructive residual stress measurement techniques cannot be used since they are unable to measure the stresses deep within the component. Measurement techniques which involve mechanical strain relie...

Although there are many simulations of residual stresses in quenched steel components there is little validation of these predictions particularly when the components are large. This is not surprising bearing in mind that the application of the through thickness measurement techniques (mechanical strain relief techniques) are problematic when the c...

It is shown that the conventional ‘sheet by sheet’ analysis of residual stress measurement by the deep hole drilling method is inaccurate when in-plane stress gradients exist. The influence of the interfacial tractions is analysed by the distributed dislocation technique. Finite element modelling is used to provide data for an example residual stre...

The modified deep hole drilling technique (iDHD) has been developed to allow near yield residual stresses to be measured and has been validated for axisymmetric residual stress fields. In the present investigation, the application of the iDHD technique was extended to non-axisymmetric stress fields. First, a finite element simulation of the iDHD te...

In this work, the effect of boring on residual stress distribution in thick walled pressure cylinders after autofrettage is studied by numerical simulation using finite element method. Autofrettage is performed using mandrelling technique. The simulations are validated by experiment. In this regard, some cylinders are autofrettaged through mandrell...

To study and understand the effects of residual stresses on fracture behaviour, it is necessary to introduce well characterised and reproducible residual stresses into laboratory fracture specimens. One technique capable of providing such residual stresses is local compression, where the local compression is applied to the sides of a test specimen....

Three dimensional simulations of bolt-nut connections have been carried out using ANSYS finite element code. Three standards, ISO, Unified and Withworth for both fine and coarse threaded connections have been used for the simulations. Stress distribution and concentration factor at the root of threads have been determined from the simulations. The...

Three dimensional simulations of bolt-nut connections have been carried out using ANSYS finite element code. Three standards, ISO, Unified and Withworth for both fine and coarse threaded connections have been used for the simulations. Stress distribution and concentration factor at the root of threads have been determined from the simulations. The...

Accurate measurement of residual stress is essential if account is to be taken of residual stress in structural integrity assessments. For thick components many non-destructive residual stress measurement techniques cannot be used since they are unable to measure the stresses deep within the component. Measurement techniques which involve mechanica...

Side-punching is proposed as a method of introducing a well-defined residual stress field into a laboratory-sized test specimen. Such a specimen may subsequently be used to assess the influence of residual stresses on the fracture behavior of materials. Side-punching consists of simultaneously indenting opposite faces of a plate of material with ri...

This paper presents novel applications of the deep-hole drilling technique for residual stress measurement in components. The results outline the versatility of this technique for application in complex situations such as residual stress measurement in very thick components, components with difficult access to the measurement location, very large c...

Residual stresses play an important role in increasing and decreasing the possibility of failure. The magnitude and direction of the residual stresses is an important factor in the integrity of engineering structures, including those containing defects. Ideally, we would like to gain insight into the integrity of a structure through testing laborat...

The effect of residual stresses on fracture behaviour of ferritic steels at low temperature has been investigated using a local approach based on the Beremin model [1]. The study aims to enhance the use of local approach in failure prediction when residual stress is present. A tensile residual stress field has been introduced in the laboratory spec...

The effect of the autofrettage process on high pressure cylinders has been investigated. Both numerical and experimental techniques have been used for the investigation. It was observed that the best autofrettage pressure for raising the pressure capacity of the cylinder was the pressure Py2 which is just sufficient to bring the outer surface of th...

The aim of this paper is to examine the influence of residual stress (RS) and loading history on the subsequent low-temperature cleavage fracture resistance of ferritic steel structures such as pressure vessels. Three dimensional finite element analyses of compact tension, C(T), specimen are carried out for various RS fields (i.e. local, global, co...

Influence of residual stresses on fracture response of an Aluminum alloy is investigated. Cylindrical flat ended punching tools are employed to introduce residual stresses on 15mm thick C(T) specimens. The residual stress field resulting from Local Compression is simulated and analysed using a finite element analysis. The dependence of residual str...

The influence of residual stresses on the fracture behaviour of materials is of fundamental importance for accurate and reliable structural integrity assessments of components and structures In this paper residual stress fields are introduced into standard fracture specimens, particularly C(T) specimens, through 'local compression', or side punchin...