The Experts below are selected from a list of 2223 Experts worldwide ranked by ideXlab platform

Salvatore Pasta - One of the best experts on this subject based on the ideXlab platform.

Vincenzo Nigrelli - One of the best experts on this subject based on the ideXlab platform.

Jeffrey Vogwell - One of the best experts on this subject based on the ideXlab platform.

  • the effect of bolt clamping force on the fracture strength and the stress intensity factor of a plate containing a Fastener Hole with edge cracks
    Engineering Failure Analysis, 2009
    Co-Authors: T N Chakherlou, Babak Abazadeh, Jeffrey Vogwell
    Abstract:

    Research has been completed to establish the effect which the clamping force, resulting from torque tightening a nut and bolt, has on the fracture strength and the stress intensity geometry factor of a Fastener Hole containing a symmetrical pair of edge cracks. The work has involved the carrying out of a programme of experimental tests and also the conducting of a numerical study. The tests were carried out using specimens made from aluminum alloy, grade AL7075-T6 rectangular plate containing a central Hole with fatigue propagated edge cracks. Three batches of specimens were produced, one without a bolt inserted (for the purpose as a benchmark) and two with nut and bolts fitted but with different tightening torques applied. The joint fracture strengths were obtained using a tensile testing machine. In the numerical investigation, a finite element package was used to model the three test specimen variants used and thereby establish their stress intensity geometry factors. The numerical analyses considered the effect of parameters such as the coefficient of friction between contacting surfaces and the magnitude of the remotely applied axial load. The results show that the bolt tightening torque, and hence the plate clamping force, has a significant effect on reducing the stress intensity factor, and thus the joint fracture strength compared to bolt-less specimens.

  • Fatigue life of an aerospace aluminium alloy subjected to cold expansion and a cyclic temperature regime
    Engineering Failure Analysis, 2006
    Co-Authors: J. M. Minguez, Jeffrey Vogwell
    Abstract:

    Abstract This paper describes experimental work that was carried out to study the influence of cyclic temperature variation on the fatigue life of Fastener Holes in an aerospace aluminium alloy after they had been subjected to cold expansion. Three different batches of specimen were produced for fatigue testing. The first samples had the Fastener Hole left in the ‘as drilled’ state, the second and third batches had their drilled Holes cold expanded by directly force fitting an oversized pin through the Hole. In addition, the third batch with cold expanded Holes was then subjected to a representative range flight cycle temperature variations. The results reveal that the cyclic temperature variation, rather than relaxing the residual stress and thus the cold expansion effect, as was feared, has actually extended the fatigue life of the cold expanded Holed specimens tested. It is believed that this is because the temperature changes have tended to neutralise the local peak residual stresses which can occur at the surface faces.

  • a novel method of cold expansion which creates near uniform compressive tangential residual stress around a Fastener Hole
    Fatigue & Fracture of Engineering Materials & Structures, 2004
    Co-Authors: Jeffrey Vogwell
    Abstract:

    A recognized way of improving the fatigue resistance of a Fastener Hole is to introduce compressive tangential residual stress around it. This can be achieved by using a cold expansion method in which an oversized pin or ball is forced through the Hole to produce a local plastic region surrounded by an elastic one. Once the pin or ball is removed allowing the elastic region to spring back it results in compressive tangential residual stress around the Hole. In practise, however, it is found that such a cold expansion method creates a non-uniform residual stress distribution through the plate thickness and even tensile residual stress can be created at the entrance and exit faces. In this paper a new method of cold expansion is proposed. It uses a tapered pin with a mating tapered split sleeve and creates an almost uniform compressive residual stress around the Hole as shown by FE method. Also, fatigue tests were carried out to verify that the method does significantly improve fatigue life. Finally the tangential residual stress distribution and fatigue life improvement of this new method were compared with those of a well-established cold expansion method and it was shown that the new method is more efficient in improving fatigue life.

  • A novel method of cold expansion which creates near‐uniform compressive tangential residual stress around a Fastener Hole
    Fatigue Fracture of Engineering Materials and Structures, 2004
    Co-Authors: Jeffrey Vogwell
    Abstract:

    A recognized way of improving the fatigue resistance of a Fastener Hole is to introduce compressive tangential residual stress around it. This can be achieved by using a cold expansion method in which an oversized pin or ball is forced through the Hole to produce a local plastic region surrounded by an elastic one. Once the pin or ball is removed allowing the elastic region to spring back it results in compressive tangential residual stress around the Hole. In practise, however, it is found that such a cold expansion method creates a non-uniform residual stress distribution through the plate thickness and even tensile residual stress can be created at the entrance and exit faces. In this paper a new method of cold expansion is proposed. It uses a tapered pin with a mating tapered split sleeve and creates an almost uniform compressive residual stress around the Hole as shown by FE method. Also, fatigue tests were carried out to verify that the method does significantly improve fatigue life. Finally the tangential residual stress distribution and fatigue life improvement of this new method were compared with those of a well-established cold expansion method and it was shown that the new method is more efficient in improving fatigue life.

Abhay Sharma - One of the best experts on this subject based on the ideXlab platform.

  • Combined Cold Expansion and Friction Stir Processing of Fastener Holes in Aluminum Alloy Al-2014-T6
    Transactions of the Indian Institute of Metals, 2017
    Co-Authors: Nitin J. Panaskar, Abhay Sharma
    Abstract:

    Cold expansion is used to induce compressive stress zone, by inserting a tapered mandrel/pin or ball into an undersized Fastener Hole in order to improve fatigue life. In this paper, combined cold expansion and friction stir processing of Fastener Holes in aluminium alloy Al-2014-T6 is presented wherein the cold expansion tool rotates and thus friction stirs the cylindrical surface of a Fastener Hole while expanding it. The residual stress, surface roughness and hardness of wall of Fastener Holes are measured and SEM images are captured. The combined cold expansion method is evaluated for three conditions at tool and Fastener Hole interface, namely wet (i.e., in presence of metal working fluid), solid lubricant (i.e., in presence of Al_2O_3 nanoparticles), and dry (i.e., without any external medium). The conventional cold expansion process is compared with combined cold expansion and friction stir processing. The results indicate efficacy of using nanoparticles as a medium in combined cold expansion and surface processing of Al-2014-T6 aluminium alloy to improve surface integrity and fatigue life.

  • Combined Cold Expansion and Friction Stir Processing of Fastener Holes in Aluminum Alloy Al-2014-T6
    Transactions of the Indian Institute of Metals, 2017
    Co-Authors: Nitin J. Panaskar, Abhay Sharma
    Abstract:

    Cold expansion is used to induce compressive stress zone, by inserting a tapered mandrel/pin or ball into an undersized Fastener Hole in order to improve fatigue life. In this paper, combined cold expansion and friction stir processing of Fastener Holes in aluminium alloy Al-2014-T6 is presented wherein the cold expansion tool rotates and thus friction stirs the cylindrical surface of a Fastener Hole while expanding it. The residual stress, surface roughness and hardness of wall of Fastener Holes are measured and SEM images are captured. The combined cold expansion method is evaluated for three conditions at tool and Fastener Hole interface, namely wet (i.e., in presence of metal working fluid), solid lubricant (i.e., in presence of Al_2O_3 nanoparticles), and dry (i.e., without any external medium). The conventional cold expansion process is compared with combined cold expansion and friction stir processing. The results indicate efficacy of using nanoparticles as a medium in combined cold expansion and surface processing of Al-2014-T6 aluminium alloy to improve surface integrity and fatigue life.

  • Surface Modification and Nanocomposite Layering of Fastener-Hole through Friction-Stir Processing
    Materials and Manufacturing Processes, 2014
    Co-Authors: Nitin J. Panaskar, Abhay Sharma
    Abstract:

    This investigation studied the surface modification and nanocomposite layering of the cylindrical surface of a Fastener-Hole using friction-stir processing. A tapered tool rotates and transverses a predrilled Hole that gradually expands and simultaneously stirs the surface. The stirring modifies the Hole's cylindrical surface to help improve the hardness and resist against fatigue loading. Introduction of nanoparticles between the tool and the Hole during the friction stirring results in formation of a nanocomposite layer that further improves the fatigue performance. The process development and resulting changes in surface finish, hardness, compressive residual stress near the Hole, and fatigue life are presented; the strengthening mechanisms and their relationship with the process parameters are discussed.

Amir Hossein Shamdani - One of the best experts on this subject based on the ideXlab platform.

  • A combined upper-bound and elastic-plastic finite element solution for a Fastener Hole subjected to internal torsion
    Archive of Applied Mechanics, 2012
    Co-Authors: Amir Hossein Shamdani, Shahin Khoddam
    Abstract:

    Fastener Holes used in the mechanical joints are vulnerable to failure due to development of stress concentration at their edges. Inducing compressive residual stresses by different techniques has been the most common method to reinforce the Holes to date. In this work, a new reinforcement technique called internal torsion, which can be classified as a localized severe plastic deformation process, is proposed as an alternative to the cold expansion pre-stressing. A special specimen is designed to represent the behavior of a typical Fastener Hole during the internal torsion process. The deformation of the specimen in the vicinity of its Hole surface is studied by introducing a parametric kinematically admissible velocity field (PKAVF) within the deformation affected zone (DAZ). Calibration of the parameters in relation to the deformation of the material during the process is done by an elastic-plastic finite element solution that was performed in ABAQUS for a specimen made of interstitial free (IF) steel. Numerical analysis of the deformation is carried out to understand the process and to estimate the optimum process parameters. Subsequently, the calibrated model is used in an upper-bound solution of the problem to estimate the torque–twist response of the specimen during internal torsion. Finally, the results of upper-bound solution are compared with those of finite element analysis. There is a good agreement between the upper-bound solution and finite element results, which verifies validity of the calibrated velocity field model and the upper-bound solution based on the model for the internal torsion problem.

  • A comparative numerical study of combined cold expansion and local torsion on Fastener Holes
    Fatigue & Fracture of Engineering Materials & Structures, 2012
    Co-Authors: Amir Hossein Shamdani, Shahin Khoddam
    Abstract:

    Cold expansion and local torsion processes provide controllable strengthening mechanisms for a Fastener Hole and therefore have engineering significance. They rely on the residual stress and the accumulated shearing strain, respectively, which are difficult to measure. Due to the complex closed form solutions for these mechanisms, their numerical study is of great importance. In this work, a combination of the cold expansion and the local torsion on a Fastener Hole has been investigated numerically to evaluate the amount and nature of the total accumulated residual stresses around a Fastener Hole. Different cases of the cold expansion and the local torsion processes were modelled and studied by finite element simulation to investigate the existence of a loading case which produces a beneficial compressive residual stress field in the vicinity of a Hole. Sensitivity of the final residual stress with respect to a range of process parameters including adequate diametral interference and angle of rotation was investigated.

  • microstructure and mechanical properties of if steel deformed during plane stress local torsion
    Journal of Materials Science, 2012
    Co-Authors: Amir Hossein Shamdani, Shahin Khoddam, P F Thomson, Ali Dehghanmanshadi
    Abstract:

    Mechanical joints are inherently vulnerable to failure because the presence of the joint Hole causes a stress concentration in the vicinity of the Hole. The need for improvement of material strength around a Fastener Hole can be satisfied by severe plastic deformation (SPD) to produce ultrafine grains. The ultrafine grained (UFG) alloys produced by SPD processing possess higher strengths than their coarse-grained counterparts as a result of the reduced grain size. However, in some circumstances such as SPD processing of Al–Zn and Al–Mg alloys the decomposition of supersaturated solid solutions competes with the Hall–Petch effect and leads to a more pronounced softening of the material [1]. Another drawback of SPD processes is that they involve bulk deformation and large energy consumption [2]. It is therefore desirable to enhance the global behaviour of the material by limiting improvement of the material property by SPD to the location at which it is needed. Localized severe plastic deformation (LSPD) techniques, such as forward spiral extrusion [3] and friction stir processing [4], involve lower energy consumption. They modify the properties of materials locally and create a gradient of grain refinement, resulting in significant improvement in the mechanical properties of the processed samples. However, these techniques cannot be used for strengthening the material around Fastener Holes, and thus a method for improving the strength of material around the Hole is needed. To reinforce the mechanical properties of material around a Hole, the plane stress local torsion (PSLT) process, which involves a plane stress axi-symmetric torsional loading, is introduced. The PSLT takes advantage of large shearing strains induced around the intended Hole position, through torsional deformation [5]. As a result, the material flows plastically within a thin annular zone around the Fastener Hole (AZFH). Because of the limited penetration of the flow localization zone into the material, a major proportion of deformation energy is consumed within the AZFH. The PSLT therefore consumes much less energy than do bulk grain refinement techniques.