A Research Report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfillment of the requirements for the degree of Master of Science in Engineering(Mechanical Engineering 30 January 2017 / An extensive variety of experimental techniques exist to determining residual stresses, but few of these techniques is suitable, however, for finding the residual stresses that exist in orthotropic or anisotropic layered materials, such as carbon-fibre reinforced polymers (CFRP). Among these techniques, particularly among the relaxation techniques, the incremental hole-drilling technique (IHD) has shown to be a suitable technique to be developed for this purpose. This technique was standardized for the case of linear elastic isotropic materials, such as the metallic alloys in general. However, its reliable application to anisotropic and layered materials, such as CFRP materials, needs to be better studied. In particular, accurate calculation methods to determine the residual stresses in these materials based on the measured in-depth strain relaxation curves need to be developed. In this work, existing calculation methods and already proposed theoretical approaches to determine residual stresses in composite laminates by the incremental hole-drilling technique are reviewed. The selected residual stress calculation method is implemented using MATLAB. For these calculations, specific calibration coefficients have to be numerically determined by the finite element method, using the ANSYS software. The developed MATLAB scripts are then validated using an experimental procedure previously developed. This experimental procedure was performed using CFRP specimens, with the stacking sequence [0o, 90o]5s and, therefore, this composite laminate was selected as case study in this work. Some discrepancies between the calculated stresses using the MATLAB scripts and those imposed during the experimental calibration procedure are observed. The errors found could be explained considering the limitations inherent to the incremental hole-drilling technique and the theoretical approach followed. However, the obtained results showed that the incremental hole-drilling can be considered a promising technique for residual stress measurement in composite laminates. / MT2017

<div>Process induced dimensional changes in composite parts has been the topic of interest for many researchers. The residual stresses that are induced in composite laminates during curing process while the laminate is in contact with the process tool often lead to dimensional variations such as spring-in of angles and warpage of flat panels. The traditional trial-and-error approach can work for simple geometries, but composite parts with complex shapes require more sophisticated models. When composite laminates are subjected to thermal stresses, such as the heating and cooling processes during curing, they can become distorted as the in-plane and the throughthickness</div><div>coffcients of thermal expansion are different, as well as chemical shrinkage of the resin, usually cause spring-in. Deformed components can cause problems during</div><div>assembly, which significantly increases production costs and affects performance. This thesis focuses on predicting these shape deformations using software simulation of composite manufacturing and curing. Various factors such as resin shrinkage, degrees of cure, difference between through thickness coefficient of thermal expansion of the composite laminate are taken into the consideration. A cure kinetic model is presented which illustrates the matrix behavior during cure. The results obtained using the software then were compared with the experimental values of spring-in from the available literature. The accuracy of ACCS package was validated in this study. Analyzing the effects of various parameters of it was estimated that 3D part simulation is an effective and cost and time saving method to predict final shape of the composite part.</div>

Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / Includes bibliographical references. / M.S.

Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / Microfiche copy available in Archives and Engineering. / Includes bibliographical references. / M.S.

This research focused on demonstrating the effectiveness of a new inelastic material model, τBTR, and was compared with an existing modified tangent modulus model, τTM, at matching the limit load response of detailed finite element models of steel frames. The influence of stiffness reduction was studied on seven W8x31 columns and eleven benchmark frames. The column study considered minor axis bending with L/r ratios of 40, 60, 80, 100, 120, 180, and 200. Limit load analyses were conducted on steel frames with major-axis and minor-axis bending. The extent of yielding and lateral displacements were evaluated for all benchmark frames at the collapse condition. Discussion is given regarding the two material models and their ability to match the limit load responses of the finite element models. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

Abstract not available

There are many causes of structural failure. One of the most important factors leading to material failure is residual stress. This stress represents effects left in structures after processing or removal of external loads including changes in shape and crystallite size. In aggregate, residual stress changes the mechanical behaviour of materials. Various measurement techniques encompassing destructive, semi destructive, and non-destructive testing can be used to measure residual stresses. Thin plates are common in engineering applications. This thesis analyzes residual stresses on circular AISI 1020 steel alloy plates after removal of external loads using two-dimensional X-ray diffraction. Two identical thin circular plates are used in this experiment; one of which is statically loaded. The other plate is used as a control specimen. Residual stresses in the plates are measured using two-dimensional X-ray diffraction and the measurements are compared to those obtained using finite element analysis. It was found that experimentally measured residual stress occurred due to manufacture processing. Also, modules A and B showed the external effect of applying not enough to reach the plastic region to deform specimen 2 and obtain residual stress results distribution.

The objective of this thesis project was to compare the stress behaviour in thermal barrier coatings (TBCs) with FE analyses in both 2D and 3D. The main focus was to analyse the vertical stresses in the topcoat (TC) and how they varied in relation to different thicknesses of the thermally grown oxide (TGO), spraying methods of the bondcoat (BC) and the topography of the BC. For the 2D simulations six samples were used; three with BCs sprayed with high-velocity oxy-fuel spraying and three sprayed with atmospheric plasma spraying. The samples had been exposed to isothermal heat treatment at 1150 °C for 0, 100 and 200 hours. Five images of each sample were taken with a scanning electron microscope, resulting in a total of 30 images. FE simulations based on these 30 images were done simulating a cooling from 1100 °C to 100 °C. The 3D simulations were based on surfaces created from coordinates measured with stripe projection technique on three samples consisting of only substrate and BC. Three domains of each sample had been measured and three CAD models based on randomly selected surfaces of each domain were made, resulting in 27 CAD models. The CAD models were used in the 3D FE simulations also simulating a cooling from 1100 °C to 100 °C. The results showed that the 2D simulations corresponds to published assertions about a stress inversion after TGO growth and that cracking will propagate from one peak to another, presuming the roughness of the TGO can be expressed as a wave. No conclusions of differences between spraying methods of the BC could be drawn. The stress inversion phenomenon was also found in the 3D simulations. By inspecting the TGO/TC-interface profile in different sections of a 3D model, difficulties in predicting the stress behaviour in a TBC with 2D were explained. No differences in stresses in relation to the BC roughness could be stated.

Abstract The effects of residual stresses distribution and post-weld-shift on the signal coupling efficiency of an Optical Add & Drop Multiplex (OADM) are investigated in this thesis. The position variations between the two collimators in the OADM under the temperature cycling test and high temperature aging test have been simulated and studied. The finite element method package, i.e. MARC, is used for the stresses and deformation simulations of an OADM under different load cases. The coupled thermal-elastic-plastic model is employed in the analysis, and the creep effect of the solder is considered in the numerical simulations. The temperature dependent material properties of the 63Sn/37Pb and 96.5Sn/3.5Ag solder are used for the solder solidification, temperature cycling and aging tests. The effects of the OADM packaging parameters, i.e. the different offset angles between collimators, different solder are also studied. Besides, the same simulation and analysis has also applied on the soldering with and without cavity. A comparison between the simulated and measured results indicates that the proposed finite element model is feasible for analyzing the OADM packaging problems.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 433-456).