We investigate the post-weld-shift(PWS) induced fiber alignment shift in butterfly laser packaging. For high-speed laser modules in lightwave communication systems, the butterfly laser modules are widely used. When laser welding is applied to assemble a butterfly package, it is usually necessary to have mechanical elements such as substrates, fiber ferrule, and clip of house materials to facilitate fiber handing and retention within the package. However, during the process, rapid solidification of the welded region and associated material shrinkage often cause a post-weld-shift between welded components. The PWS significantly affects the package yield. A novel measurement and compensation technique employing a high-magnification camera with image capturing system (HMCICS) to probe the post-weld-shift (PWS) induced fiber alignment shifts in high-performance butterfly-type laser module packages is studied. The results show that the direction and magnitude of the fiber alignment shifts induced by the PWS in laser-welded butterfly-type laser module packaging can be quantitatively determined and then compensated. The increased coupling efficiency after this PWS compensation was from 3% to 10%. This HMCICS technique has provided an important tool for quantitative measurement and compensation to the effect of the PWS on the fiber alignment shifts in laser module packages. Therefore, the reliable butterfly-type laser modules with a high yield and a high performance used in lightwave transmission systems can be developed.

A notch clip approach to compensate post-weld-shift(PWS) induced by laser welding process in butterfly type laser module packages is investigated. For high-speed laser modules in lightwave communication systems, the butterfly laser modules are widely used. When laser welding is applied to assemble a butterfly package, it is usually necessary to have mechanical elements such as substrates, fiber ferrule, and clip of house materials to facilitate fiber handing and retention within the package. However, during the laser welding process, rapid solidification of the welded region and associated material shrinkage often cause a post-weld-shift between welded components. The PWS significantly affects the package yield. A notch clip approach and measurements employing a high-magnification camera with image capturing system (HMCICS) to probe the PWS induced fiber alignment shifts and welding compensation on notch in high-performance butterfly-type laser module packages are studied. The results show that the direction and magnitude of the fiber alignment shifts induced by the PWS in laser-welded butterfly-type laser module packaging can be quantitatively determined and then compensated. The overall coupling efficiency after this PWS compensation was from 80¢H to 90¢H. This notch approach and HMCICS technique have provided an important tool for quantitative measurement and compensation to the effect of the PWS on the fiber alignment shifts in laser module packages. Therefore, the reliable butterfly-type laser modules with a high yield and a high performance used in lightwave transmission systems can be developed.

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Existing steel bridges are subjected to both increasing traffic loads and natural aging, both are capable of causing severe durability problems. Dependable rehabilitation methods are attracting attention as the promising methods to enhance structural durability and/or structural performance. One possible rehabilitation method, for improving fatigue performance, is the use of residual stress-based post-weld treatments such as peening. A number of studies has been performed and it has been proven that residual stress-based treatments are an effective way of increasing the fatigue lives of newly built steel bridges, and even enhancing the fatigue performance of existing structures. Provisions have been developed to ensure the proper execution of peening and several codes have considered its beneficial effect in the fatigue design of welded structures. Various analytical approaches are used to predict the fatigue performance of welded structures and the beneficial effects of residual stress-based post-weld treatments. In most codes and recommendations, variations of the “S-N curve” approach are employed. Linear elastic fracture mechanics (LEFM) and strain-based fracture mechanics (SBFM) are widely accepted approaches for making more precise predictions of the treatment benefit. Cohesive zone fatigue models are also recently introduced for predicting fatigue crack growth in as-received and peened welds. Despite all the research conducted, there are still two main unanswered questions related to the application of peening treatments. First, it is claimed that peening can be more effective for civil structures where a considerable portion of the total applied stress is due to permanent loads and thus peening is applied under load. However, most of research done so far has studied effects peening prior to the introduction of the structural self weight. Secondly, considering the nature of these treatments, some concerns have been raised regarding their effectiveness under actual in-service loading conditions, as most of the reported test-based studies only demonstrated the fatigue performance improvement under constant amplitude tension-only loading conditions. The current study was undertaken to examine the fatigue performance of welds peened-under load and to determine the effectiveness of peening for improving the fatigue performance of welds subjected to realistic in-service loading conditions. Moreover, a previously developed strain-based fracture mechanics (SBFM) model for predicting fatigue performance of welded details under different loading and treatment conditions, and a previously developed damage-based cohesive zone model for steel specimens were evaluated and calibrated. Fatigue tests were conducted on welded steel specimens, simulating different loading and peening conditions. Dye penetrant was used to stain cracked specimens upon detection of cracks and a crack front marking loading scheme was used to study the crack front shape. The alternating current potential drop (ACPD) method was used for continuous crack growth monitoring for both as-welded and peened specimens under different loading schemes. It was observed that cracks propagated at different rates in specimens treated under load than in the normally peened and as-welded specimens. Material tests were also conducted to determine the mechanical properties of the steel base metal. Secondary effects of peening were investigated by microhardness measurements and weld toe measurements. A number of typical weld toe defects was also detected. Residual stress measurements showed a uniformly distributed tensile residual stress near the surface of the untreated specimen. Needle peening the specimen resulted in a significant change in the residual stress distribution through the specimen thickness. In all cases, peening resulted in a significant increase in the fatigue life. However, greater fatigue life improvements were observed in lower stress ranges. Of the specimens tested under constant amplitude loading, those peened under load experienced the largest fatigue lives. For the variable amplitude loading tests, the untreated specimens had mean fatigue lives slightly less than observed in the constant amplitude tests. A previously developed strain-based fracture mechanics (SBFM) model was used to estimate analytically the effectiveness of peening applied to welded details. The model was able to predict the fatigue lives for both the as-welded and peened specimens for all loading conditions. It correctly estimated the additional benefit of peening when applied under a relatively small prestress level. The model predictions were used to estimate the additional benefit of peening under load. A previously developed cohesive zone model was introduced and applied to predict fatigue crack growth in a weld detail under cyclic loading. Fatigue tests were simulated using the finite element program ABAQUS. The material parameters α and β were chosen by iteration. Other fatigue tests were simulated and the model correctly predicted the effects of varying the applied stress range, R ratio, and residual stress level on the fatigue behaviour.

A novel technique by employing a capacitance displacement measurement system to measure the post-weld-shift (PWS) caused by laser welding in the butterfly-type laser diode module packaging process is proposed. Reduction of the PWS is an important issue in developing low-cost and high-performance semiconductor laser module. Prior to the reduction and compensation of the PWS, a measurement system of PWS must be constructed. In comparison to the high-magnification camera with image capturing system (HMCICS) limited in resolution of 0.07£gm due to its pixels, a measurement system with a higher resolution of 0.0254£gm is used. During the measurement procedure, the PWS of the ferrule probed by the sensors is converted into the fiber misalignment shifts. The coupling efficiency can be improved over 70% after compensation. The result indicates that the PWS can be qualitatively measured and quantitatively computed.

The energy absorbing behavior of stainless steel 304L during the pulsed Nd:YAG laser welding is investigated in this thesis. The equivalent absorptivity is estimated from the comparison of measured and finite element method (FEM) results simulated melting pool shape parameters, e.g. pool width, pool depth, cross-section area and total volume of the pool. To simulate the actual pulsed laser beam, the energy density of heating source is performed as a Guassian distribution in the transection of a circular laser beam. For evaluating the feasibility and the accuracy of the estimated equivalent absorptivity, the multi-pulsed Nd:YAG laser welding is simulated by using the estimated absorptivities. A good agreement between this simulated and measured melting pool shapes are found in the multi-pulsed laser welding. The equivalent absorptivity can be interpolated from different parameters of the molten pool. However, absorptivity curve fitted from the cross-section area and total volume of the melting pool provide a more stable value. Results also indicate that the absorptivity and the pulse energy are in inverse proportion. The thermal-elastic-plastic FEM model is employed to simulate the fusion and solidification process of the pulsed laser welding. A complicate residual stress distribution introduced from the shrinkage in the solidification process is also calculated and presented. The distribution of post-weld-deformation near the melting pool has also been studied in this thesis. This post-weld-deformation may be a key factor in high precision laser welding, e.g. laser packaging for the optoelectronic components. The absorptivity estimated in this thesis may be helpful to simulate the laser welding process accurately.

In this study, the capacitance displacement system (CDS) is employed to measure the post-weld-shift (PWS) induced by laser welding in butterfly type laser module package. The advantage of CDS is able to simultaneously and immediately measure the direction and the magnitude of PWS. Furthermore, with the aid of notch clip, the PWS can efficiently and quantitatively be compensated by laser hammering technique to regain the coupling power. Reduction of the PWS is an important issue in developing low-cost and high-performance laser modules. The package yield of laser modules can be imp roved due to the real-time measurement and quantitative compensation. In comparison with the high-magnification camera with image capturing system (HMCICS) having 0.7£gm resolution, the capacitance sensor achieves 25.4nm and 0.1£gm in its resolution and accuracy, respectively. Besides, during the package procedure, the real-time displacement detection can be used to adjust the package parameters. As a result, the PWS is reduced that contributes to less coupling power loss. After welding, the result reveals that the PWS was measured as X=0.15£gm and Y=-4.58£gm, while the coupling power is 43.19%.

Existing steel bridges are subjected to both increasing traffic loads and natural aging, both are capable of causing severe durability problems. Dependable rehabilitation methods are attracting attention as the promising methods to enhance structural durability and/or structural performance. One possible rehabilitation method, for improving fatigue performance, is the use of residual stress-based post-weld treatments such as peening. A number of studies has been performed and it has been proven that residual stress-based treatments are an effective way of increasing the fatigue lives of newly built steel bridges, and even enhancing the fatigue performance of existing structures. Provisions have been developed to ensure the proper execution of peening and several codes have considered its beneficial effect in the fatigue design of welded structures. Various analytical approaches are used to predict the fatigue performance of welded structures and the beneficial effects of residual stress-based post-weld treatments. In most codes and recommendations, variations of the “S-N curve” approach are employed. Linear elastic fracture mechanics (LEFM) and strain-based fracture mechanics (SBFM) are widely accepted approaches for making more precise predictions of the treatment benefit. Cohesive zone fatigue models are also recently introduced for predicting fatigue crack growth in as-received and peened welds. Despite all the research conducted, there are still two main unanswered questions related to the application of peening treatments. First, it is claimed that peening can be more effective for civil structures where a considerable portion of the total applied stress is due to permanent loads and thus peening is applied under load. However, most of research done so far has studied effects peening prior to the introduction of the structural self weight. Secondly, considering the nature of these treatments, some concerns have been raised regarding their effectiveness under actual in-service loading conditions, as most of the reported test-based studies only demonstrated the fatigue performance improvement under constant amplitude tension-only loading conditions. The current study was undertaken to examine the fatigue performance of welds peened-under load and to determine the effectiveness of peening for improving the fatigue performance of welds subjected to realistic in-service loading conditions. Moreover, a previously developed strain-based fracture mechanics (SBFM) model for predicting fatigue performance of welded details under different loading and treatment conditions, and a previously developed damage-based cohesive zone model for steel specimens were evaluated and calibrated. Fatigue tests were conducted on welded steel specimens, simulating different loading and peening conditions. Dye penetrant was used to stain cracked specimens upon detection of cracks and a crack front marking loading scheme was used to study the crack front shape. The alternating current potential drop (ACPD) method was used for continuous crack growth monitoring for both as-welded and peened specimens under different loading schemes. It was observed that cracks propagated at different rates in specimens treated under load than in the normally peened and as-welded specimens. Material tests were also conducted to determine the mechanical properties of the steel base metal. Secondary effects of peening were investigated by microhardness measurements and weld toe measurements. A number of typical weld toe defects was also detected. Residual stress measurements showed a uniformly distributed tensile residual stress near the surface of the untreated specimen. Needle peening the specimen resulted in a significant change in the residual stress distribution through the specimen thickness. In all cases, peening resulted in a significant increase in the fatigue life. However, greater fatigue life improvements were observed in lower stress ranges. Of the specimens tested under constant amplitude loading, those peened under load experienced the largest fatigue lives. For the variable amplitude loading tests, the untreated specimens had mean fatigue lives slightly less than observed in the constant amplitude tests. A previously developed strain-based fracture mechanics (SBFM) model was used to estimate analytically the effectiveness of peening applied to welded details. The model was able to predict the fatigue lives for both the as-welded and peened specimens for all loading conditions. It correctly estimated the additional benefit of peening when applied under a relatively small prestress level. The model predictions were used to estimate the additional benefit of peening under load. A previously developed cohesive zone model was introduced and applied to predict fatigue crack growth in a weld detail under cyclic loading. Fatigue tests were simulated using the finite element program ABAQUS. The material parameters α and β were chosen by iteration. Other fatigue tests were simulated and the model correctly predicted the effects of varying the applied stress range, R ratio, and residual stress level on the fatigue behaviour.

CCI Valve Technology AB is a company located in Säffle, Sweden, that manufactures and installs bypass valves. Due to requirements outside normal standards on the valve's hardness values, some measurements have had difficulties meeting such requirements. During this thesis work, tests were carried out to determine how to overcome the difficulties. The experiments focused on five different areas that may affect the components hardness, welding method, soaking temperature during post weld heat treatment, measuring procedure, component thickness and number of heat treatment cycles. The Grade 91 steel specimens that were examined consisted of five solid cylinders and three various pipes that were welded together by using shielded metal arc welding (SMAW) or gas tungsten arc welding (GTAW). Each pipe was sawed apart into three equal parts. All specimens were hardness tested and eight of the specimens' microstructure was studied with an optical microscope. The hardness measurement instruments used, LECO V-100-C2 and GE-MIC 10, are Vickers hardness testers, one stationary and the other one portable. The measuring results contain a vast number of different hardness measurement data. From the analyzed data, the conclusions were drawn that the most suitable soaking temperature during post weld heat treatment were 750° C, that the SMAW method creates a more stable hardness profile than the GTAW method, and that one heat treatment cycle is more beneficial than two or more.

This dissertation presents the results of an investigation into the corrosion resistance of friction stir welding (FSW) for aerospace structures. Two of the most common aerospace aluminum alloys, 2024 and 7075, were investigated. In the as-welded condition, both alloys were found to be highly susceptible to exfoliation corrosion, and 7075 was found to be susceptible to stress corrosion cracking as well. The goal of this research was to identify proper initial temper selection and postweld aging treatments for enhancing the corrosion resistance of both 2024 and 7075 alloys, and their dissimilar joints. A large number of heat treatments were investigated for 7075 in the T6 and T73 tempers, including retrogression re-aging (RRA). Heat treatments were also investigated for 2024-T3 and 2024-T81. Samples were evaluated for resistance to exfoliation corrosion using optical microscopy. Microhardness, electrical conductivity, tension, and fatigue crack propagation tests were also performed on the samples. Beneficial heat treatments were found for both alloys as well as for their dissimilar joints. / "December 2005." / Thesis (Ph.D.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering