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A Study for Failure Test and Progressive Failure Analysis on Composite Laminate Joints

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초록 moremore
The use of mechanical joints in composite airframes has increased with the expansion of airframe composite material applications. The expansion includes non-structural parts such as interior walls or ducts, as well as secondary or primary parts such as exterior fairings, floor panels, pressure bulkh...
The use of mechanical joints in composite airframes has increased with the expansion of airframe composite material applications. The expansion includes non-structural parts such as interior walls or ducts, as well as secondary or primary parts such as exterior fairings, floor panels, pressure bulkheads, wing reading edges or spars. Mechanical fastening is a common method used in airframe assembly work in which materials must be joined. Various mechanical fasteners are used to join metallic and composite parts joining. Fastener types depend on joint types and the load being applied to the fastener. To ensure that composite structures achieve safe, robust designs, tests and analyses are required to facilitate the verification of the lower level building blocks needed to produce composite components. At the lower level, building block tests are conducted to characterize material performance. This is usually called the coupon test. Above this level, testing is carried out on the elements and details. These levels help determine the complexity and further characteristics of the parts. In general, composite materials properties are defined as mechanical properties and they include the stiffness and strength used for mechanical design and analysis. The American Society for Testing and Materials (ASTM) defines tests for each property and describes the detailed procedures. ASTM also guides the standard specimen conditioning procedures for low or elevated temperatures with moisture absorption. Composite laminate failure theories have continued to receive considerable attention. In terms of stress analysis, the most popular failure theories are maximum stress, maximum strain, Tsai-Wu and Puck failure criteria. Additional theories on failure mechanism are under development. Recently, a study conducted by the World-Wide Failure Exercise (WWFE) compared failure theories according to blind standard tests and results. In this study, each failure theory was used to predict specimen failure. The progressive failure analysis (PFA) method is also used to analyze composite laminate failure behavior and laminated composites failure according to fiber breakage, matrix cracking, or layer delamination. These modes depend on the loading, stacking sequence, and specimen geometry. The initial failure of a lamina in a laminated structure can be predicted and analyzed using the failure criterion with the first-ply failure theory. The total failure prediction requires an understanding of the failure mode and the mechanism of the laminate or structure. To analyze and simulate a progressive failure in the FEM, the material property model is required both before- and post-failure depending on the material characteristics. With the aforementioned studies, significant research has been conducted in various subjects – e.g. joint strength, the FEM method, failure theories, design methods and test verification. However, it is not feasible to combine these papers into a single general design guide or tool to facilitate the manufacture of composite joint from the design stage to the verification stage. To achieve this, the aforementioned studies and applications should be applied to general composite materials. Accordingly this paper endeavors to apply the existing studies and methods with standard test results for composite mechanical joints and evaluate the results. CYCOM® 5276-1 G40-800 tape is used as a base material to make the laminates and test specimens. To develop the mechanical and physical properties of the laminate, the ASTM specifications are applied as properties. Mechanical joint test for a composite laminate are defined in ASTM D5961 and D7332 according to joint types. In general, a lap joint is defined as a single or double lap joint (in-plane mode). The major load is transferred via the shear load on the fastener in the joint. The tension load is transferred via fastener tension load in a pull-through joint. A comprehensive procedure for a mechanically fastened composite laminate joint (ASTM D5961 Proc. A, B) is demonstrated from fixture design to analysis of test results. To design and analyze composite laminate mechanical joint, joint parameters such as joint area dimensions, joint type, fastener type and joining torque should be considered as parameters. To analyze the double and single shear joints of the composite laminates, FEM model was created reflecting the detailed test L/BCs. The 2D FEM model reflected the fixture, specimen and fastener by using the RBE. The 3D FEM model also reflected the fixture, specimen and fastener with the contact condition between the specimen and fastener model. The 3D FEM model for the test fixture was created to simulate the total test component and analyze the fixture effect for the FEM results. The MSC Patran/Nastran Solution 400 was used as a solver to analyze the ASMT D5961. To predict the maximum load in the analysis, laminate failure theories and the PFA method were used in 3.3. For the material degradation model, immediate and gradual options in 2.2 were applied to the analysis. The test result graphs were transformed to load-displacement graphs to allow a comparison with the analysis result graphs. The 2D and 3D FEM results included the fixture and specimen deformations with loads for each analysis increment result. The FEM results show the same failures. In addition, the maximum load is within 15% relative error (30% including Tsai-Wu) for the double shear test load and failure mode. The FEM results applied to the maximum stress and maximum strain failure theories were close to the test results. The FEM results show that the maximum load was within 30% relative error (50% including maximum strain and Tsai-Wu) for the single shear test load. The relative error of the single shear test was significantly higher than that of the double shear test. The applied analysis solution 400 and PFA method had the limitation to the analysis on the excessive progressive failure areas, fastener head fail (E3H) or fastener grip fail (T3T). The analysis method was suitable to predict the initial range for test and maximum test load. However, it was not sufficient to represent the total range of test by the PFA method. To improve the limitation and analyze the total range of test, exact material degradation model for excessive progressive failure zone and failure model on fastener should be included in the PFA. ASTM D7332 Proc. B was designed to produce fastener pull-through resistance for a composite laminate structural joint. The test load is normally applied to the specimen via the fastener. Laminate thickness and fastener types (diameter, shear or tension, protruding or countersunk) are general parameters to conceptually access the pull-through resistance or allowable load. Composite laminate pull-through resistance was analyzed using the FEM and compared with the test results. The 2D and 3D FEM models, a nonlinear analysis, and a progressive failure analysis utilizing three composite laminate failure theories maximum stress, maximum strain, and Tsai-Wu were used to predict the FEM results with the test results. The L/BCs of the test were applied to the FEM to simulate the test. A composite laminate pull-through test (ASTM D7332 Proc. B) was designed with a special fixture to collect more precise data. The results show that the relative differences in laminate and fastener strength affect the test results. In addition, the failure mode, laminate stacking sequence, and fastener type are major parameters. The PFA and composite failure theory was used to analyze the pull-through test results. The 2D FEM results are close to the real test behavior until to the initial failure. However, the predictive quality of the results is limited to the initial failure. The suggested FEM is an efficient method of producing expectations as well reproducing the pull-through resistance of composite laminate joint within a 35% relative error.
목차 moremore
Chapter Ⅰ Introduction 1
1.1 Composite Material Applications in Aircraft, Vehicles and Other Structures 1
1.2 Design for Composite Mechanical Joint 7
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Chapter Ⅰ Introduction 1
1.1 Composite Material Applications in Aircraft, Vehicles and Other Structures 1
1.2 Design for Composite Mechanical Joint 7
1.3 Test and Analysis for Composite Material Joint 7
1.4 Recent Studies and Results 10
1.5 Objectives (Scope) and Study Flow Chart 20

Chapter Ⅱ Theory and FEM Analysis Method 22
2.1 Lamination Theory 22
2.2 Progressive Failure Analysis (PFA) 25
2.3 User Defined Material Model (UFAIL) and User Defined Stiffness Degraded Model (UPROGFAIL) for PFA 30

Chapter Ⅲ Composite Material and Properties 34
3.1 Composite Material 34
3.2 Composite Material (Lamina) Properties 37
3.3 PFA Application for Laminates 39

Chapter Ⅳ A Study on Composite Laminate Bolted Joints 48
4.1 Problem Description 50
4.2 Test and Fixture Design 57
4.3 Test Results and Failure Modes 61
4.4 FEM Modeling and Analysis 71
4.5 Test and FEM Analysis Review 78

Chapter Ⅴ A Study on Composite Laminate Pull-through Joint 86
5.1 Test and FEM Analysis 87
5.2 Test Results and Failure Modes 92
5.3 FEM Modeling and Analysis 98
5.4 Test and FEM Analysis Review 101

Chapter Ⅵ Conclusion 109