Pull-through failure of bolted composite joints
Bibliographic record
Abstract
The design and certification of composite aircraft structures requires extensive and costly testing of bolted joints since no robust predictive tools are available. The majority of investigations in this field focus on the shear loading of bolted carbon fibre-reinforced polymer matrix composites while studies on the behaviour of pull-through are limited. Thus, this work presents an extensive investigation of the factors affecting bolted composite panels subjected to out-of-plane loading with the objective to develop a semi-empirical predictive model. First, an experimental investigation is presented where the influence of fastener size and laminate thickness was systematically studied. The effect of the laminate layup and fastener clamping torque was also examined. Specimens manufactured from out-of-autoclave carbon-epoxy prepregs were transversely loaded in an electromechanical testing machine. The load-displacement response was measured and the failure mechanisms were examined by optical microscopy. Relatively thick specimens were used to ensure that the head depth of the countersink fasteners did not exceed seventy percent of the laminate thickness. Second, numerical analysis was conducted to predict joint failure by using a simplified axisymmetric 3-D finite element approach. Contact elements were used under the region of the fastener head and the failure was predicted using the maximum principal strain criterion. The experimental results showed that failures were dominated by inter-ply delamination and through-thickness shear failure of the laminate. A conical damage zone was found under the fastener head with damage radially dispersed from the fastener hole. The opening angles of the cones varied with the fastener head geometry. The load-displacement behaviour was affected by the fastener type. The finite element analysis showed that a concentrated shear stress area under the fastener head caused the cone damage initiation. Maximum fibre direction stresses and out-of-plane shear were both found near the fastener hole on the opposite side of the loading face. Transverse deformation and inter-laminar shear caused the final failure in the form of inter-ply delamination. The numerical analysis also indicated that the pull-through load resistance was more sensitive to the contact area under the fastener head and the head geometry than to the fastener shank size. Finally, a semi-empirical equation for the prediction of the pull-through resistance that includes the joint characteristic factors was developed.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".