To design a bolted joint, the transition bearing stress and maximumbearing stress have to be regarded. Transition bearing stress is thebearing stress where bearing failure begins and maximum bearing stressis where the joint goes to total failure. A method for studying rotationin a bolted joint has been developed using an optical instrument calledDigital Speckle Photography, DSP, which is a non-contact extensometerusing digital cameras, together with a load frame. The data from DSPsystem is transformed and analyzed to get rotations for different partsof the joint. Thinner joints give higher values on transition bearingstress, higher maximum bearing stress and higher maximum bolt rotation,than thicker joints. Bolt torque has a big impact and higher torquegives the same positive results as thinner joints. Increased secondarybending makes the joint more resistant to bearing failure, whichincreases the transition bearing failure stress, maximum bearing failurestress and maximum bolt rotation. There is a relationship between thecurve slope in a bearing stress versus bolt rotation figure and thetransition bearing stress. If the joint has a lower value on boltrotation, in comparison with other joints, at the same bearing stress,this will lead to a higher transition bearing stress.

No / Composite structure incorporating steel beams and precast hollowcore slabs is a recently developed composite floor system for building structures. This form of composite construction is so far limited to simple beam-column connections. Although the concept of semi-rigid composite joints has been widely research in the past, most of the researches have been carried out on composite joints with metal deck flooring and solid concrete slabs. Research on composite joints with precast hollowcore slabs is rather limited. As the construction industry demands for rapid construction with reduction in cost and environmental impacts, this form of composite floor system, which does not require major onsite concreting, has become very popular among the designers and engineers in the UK. In this paper, full-scale tests of beam-to-column semi-rigid composite joints with steel beam and precast hollowcore slabs are reported. Based on the tests data; the structural behaviour of these semi-rigid composite joints is discussed together with numerical and finite element modelling. Through parametric studies, an analytical model for the semirigid composite joints is proposed and is verified by both the experimental data and finite element model; and good agreement is obtained.

No / This paper described the finite element modelling of the semi-rigid composite beam-column joints with the composite steel beams and precast hollowcore slabs which can accurately simulate the moment-rotation response of the connections. Using the general purpose finite element software ABAQUS, a three dimensional model of the composite joint is set up. The techniques of simulating the bolt force, the endplate, the concrete elements, the reinforcement, the shear connectors and the interaction between the slabs and the steel beams are discussed. The results are presented and compared with the experimental data and good agreement is obtained. Parametric studies using the developed model will be performed to gain better understanding of this form of composite joints.

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No / Composite construction incorporating steel beams and precast hollowcore slabs is a recently developed composite floor system for building construction. As the construction industry demands for rapid construction with reduction in cost and environmental impacts, this form of composite construction, which does not require major onsite concreting, has become very popular among the designers and engineers in the UK. This form of composite construction is so far limited to simple beam-column connections. A semi-rigid composite joint is developed which can provide sufficient moment and rotation capacity required for plastic analysis in composite beams design. An analytical model for the semi-rigid composite connection is proposed and is verified with the experimental data and good agreement is obtained.

This study is dedicated to thermoplastic composite joints obtained by an electrical resistance welding procedure. This welding process consists in joining two substrates with an electrical resistor which acts as a heating element melting the polymer substrates. The substrates considered herein are 2mm thick 7-layer hybrid composites, with the following stacking sequence ([0°/90°]G, [0°/90°]C, [45°]C, [0°/90°]C, [45°]C, [0°/90°]C, [0°/90°]G), where G and C denote plies with PPS matrix reinforced by continuous glass or carbon bres, respectively. The heating element is a stainless metallic grid surrounded by two PPS amorphous lms. For a better understanding of the the time evolution of the temperature eld in the welded zone, a heat transfer model was developed in nite element code Abaqus®. The prediction capabilities of the numerical tool were validated by comparing the numerical results with thermocouple measurements. The thermal properties required by the nite element model, viz. the specic heat and the thermal conductivities, were identied from DSC tests and from an inverse identication procedure, respectively. The inverse identication procedure is based on a Levenberg-Marquart algorithm applied to the analysis of specic experiments instrumented with thermocouples and an infra-red camera. Thermal or/and mechanical analyses of anisotropic composite laminates can lead to high computational costs even for linear analyses. Proper Generalized Decomposition constitutes a promising tool to reduce computational costs for multi-dimensional problems such as multi-parametric problems typical of manufacturing process simulations and/or problems with dierent length scales typical of composite laminates. To demonstrate its capabilities and its eciency {including in terms of computation costs for small size problems- PGD technique is applied to the solution of an axisymmetric heat transfer problem. Specimens were manufactured (with a laboratory welding machine designed and built during this study) with dierent processing parameters - eating element geometry, intensity of the electrical current, time evolution of the pressure. DCB specimens were tested to characterize the mechanical toughness under mode I. The analysis with the compliance method of the tests results exhibits two non-negligible energy dissipation mechanisms, related to crack creation and localized plastic deformation, respectively. An original model developed within the internal variable thermodynamics framework is proposed and used to describe the R-curves representative of the ductile behaviour of the DCB specimens. A rst sensitivity analysis of the processing parameters on the joint fracture toughness exhibits the key role of the pressure applied onto the joint during the cooling phase of the welding process. / Este estudo é dedicado a juntas de compósitos termoplásticos soldadas pelo processo de soldagem por resistência elétrica. Este processo consiste em unir dois substratos com um resistor elétrico que atua como um elemento de aquecimento que funde o polímero dos substratos. Os substratos considerados neste trabalho são laminados compósitos híbridos, constituídos de 7 camadas que totalizam 2 mm de espessura, com a seguinte sequencia de empilhamento ([0°/90°]G, [0°/90°]C, [45°]C, [0°/90°]C, [45°]C, [0°/90°]C, [0°/90°]G), onde G e C denotam camadas de PPS reforçadas com fibra de vidro ou carbono, respectivamente. O elemento de aquecimento utilizado é uma malha metálica de aço inoxidável entre dois filmes de PPS (amorfos). Para um melhor entendimento do histórico do campo de temperatura na região soldada, um modelo de transferência de calor foi desenvolvido no pacote de elementos nitos Abaqus®. As capacidades de predição de temperatura do modelo computacional foram validadas a partir da comparação com resultados experimentais de termopares. As propriedades térmicas do modelo em elementos nitos, viz. o calor específico e as condutividades térmicas, foram identificadas a partir de ensaios DSC e de um procedimento de identificação inverso, respectivamente. O procedimento de identificação inversa foi baseado no algoritmo de Levenberg-Marquart aplicado na análise de experimentos específicos intrumentados com termopares e com uma câmera infra-vermelha. A análise térmica ou/e mecânica de laminados compósitos anisotropos podem apresentar elevados cusos computacionais, mesmo para análises lineares. A técnica PGD (Proper Generalized Decomposition) é uma ferramenta promissora na redução de custos computacionais de problemas multidimensionais, tópicos de simulação do processo de manufatura, e/ou problemas multi-escalas, tópico de laminados compósitos. Para demonstrar sua capacidade e sua eficiência, a técnica PGD é aplicada na solução de um problema axissimétrico de transferência de calor. Corpos-de-prova foram fabricados (com a máquina de soldagem laboratorial desenvolvida e construída durante este estudo) com diferentes parâmetros de processamento - geometria do elemento de aquecimento, intensidade da corrente elétrica, histórico de pressão. Corpos-de-prova DCB foram testados para caracterizar a resistência mecânica à propagação de trinca em modo I. A análise com o método da exibilidade dos resultados mostram dois mecanismos predominantes de dissipação de energia, correlatos com a criação da trinca e a localização de deformação plástica, respectivamente. Um modelo original desenvolvido baseado nas variáveis internas termodinâmicas é proposto e usado para descrição das curvas-R representativas do comportamento dúctil dos corpos-de-prova DCB. Uma primeira análise de sensibilidade da resistência à fratura ao variar os parâmetros de processamento mostra que a pressão aplicada na junta durante a etapa de resfriamento desempenha papel fundamental na resistência final da junta.

Results from a research program to investigate the long term effects of through-the-thickness fastener clamp-up force (preload) relaxation on the strength of mechanically fastened joints for two graphite/thermoplastic composite materials (Dupont's IM6/KIII and ICI-Fiberite's IM8/APC(HTA)) are summarized and compared with analytical methods. An experimental program was conducted in which 56 mechanically fastened single-shear joints were tested. Phase I static tests established joint bearing strength as a function of clamp-up force for two types of fasteners (protruding head and countersink) with no relaxation of preload. Phase II testing monitored short-term fastener preload relaxation (up to 1 ,000 hours), with special bolt force sensor washers. Inservice parameters included were temperature, in-plane loads, and torque. The jOints were tested to failure at the end of the relaxation time period to determine any subsequent effect on joint strength. Phase I test results indicated that joint bearing strength increased by as much as twenty-eight percent over the clamp-up force range of a Ibs (fingertight) to 3,500 Ibs for both materials. Fastener head type, material, and temperature also affected the resultant bearing strength. For Phase II, fastener clamp-up force at room temperature (78°F) relaxed an average of six percent from the initial value during the short-term test period. The relaxation was projected to be as high as fourteen and sixteen percent at 100,000 hours for HTA and Kill, respectively. The elevated temperature condition (250°F) significantly increased the relaxation rate with the projected 100,000 hour relaxation amount being as high as thirty-seven percent for HTA and sixty percent for Kill. Comparison of the Phase II bearing strengths to the Phase I results indicated that portions of the data correlated well, while others did not. It was concluded that relaxation of the clamp-up force over the short-term time period did not significantly lower the bearing strength of either material, however an extended exposure to 250°F could affect the bearing strength. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering.

Joints represent a design challenge, especially for composite structures. Among the available joining methods, co-curing is an efficient way to integrate parts for some applications. Coates and Armanios have proposed a Single Nested Overlap (SNO) co-cured joint configuration, obtained from a single lap joint through the overlap/interleafing of the adjoining top/bottom adherend plies, respectively. Through a comparative investigation, they have demonstrated joint strength and fatigue life improvements over the single lap joint counterparts for unidirectional and quasi-isotropic adherend lay-ups. This research extends the comparative investigation of Coates and Armanios by focusing upon characterizing and differentiating the damage initiation and progression mechanisms under quasi-static loading. Six specimen configurations are manufactured and tested. It is confirmed that single nested overlap joints show 29.2% and 27.4% average improvement in strength over single lap counterparts for zero-degree unidirectional and quasi-isotropic lay-ups, respectively. Several nondestructive evaluation techniques are used to observe and analyze damage initiation, damage progression and failure modes of the studied specimens and to monitor their mechanical response. Using X-ray Radiography and Optical Microscopy techniques during quasi-static loading, a physical characterization of damage and failure mechanisms is obtained. The acoustic emission data acquired during monotonic loading could reveal the overall picture of AE activities produced by the damage initiation, development and accumulation mechanisms within the specimen via parametric analysis. Further AE analysis by a selected supervised clustering method is carried out and shown successful in differentiating and clustering the AE data. Correlation with physical observations from other techniques suggests that the resulting clusters may be associated to specific damage modes and failure mechanisms.

Joints provide a path for transfer of load and are important components in an assembly of structures, particularly in translating joint strength improvements directly to significant cost savings. This cost savings is more evident in composite joints since manufacturing of more complex single piece components results in a reduction of both part count and labor. An improvement in joint strength for co-cured composite joints through minimized free-edge delamination was investigated for quasi-isotropic [0/±45/90]s lay-up based on the quantitative assessments of the quasi-static and fatigue strength and qualitative understanding of the fatigue damage initiation and propagation for the [0/±θ/90]s family of co-cured composite joints. A previously proposed co-cured joint concept, the Single Nested Overlap (SNO) joint, was compared against a Straight Laminate (SL) and a single lap joint. The SL represents a "perfect" joint and serves as an upper bound whereas the single lap joint represents the simplest generic joint and is the base design for the SNO joint concept. Three categorized failure types, which represented predominant failure modes in the SL, single lap and SNO joints, along with two different fatigue strength indicators were used for quasi-static and fatigue strength comparison. With fatigue run-out defined at 1 x 106 cycles, the fatigue damage initiation and propagation at high loadings was monitored with an Infrared Thermoelastic Stress Analysis (IR-TSA) technique, while a damage type comparison was used at low loadings. Quasi-static Acoustic Emission (AE) counts were observed to be Fatigue Limit (FL) predictors for [0/±θ/90]s SL and SNO joints. The validity of these FL predictors were also assessed in the damage type comparison.