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Hanson, Alexander Anthony

Publications and source records attributed to Hanson, Alexander Anthony.

12 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Revisiting the Pipe Bomb V&V Problem using the BCJ Material Model

For weapon safety assessments, Sandia has an interest in accurately predicting failure of pressure vessels at high temperature. In order to assess Sandia's predictive capability for these problems, a simplified validation problem for thermo-mechanical failure due to pressurization was developed and is referred to as the pipe bomb problem. In this study, several pipes were heated in a non-isothermal manner and pressurized until failure. The previous attempt to accurately predict the pipe bombs' failure pressures demonstrated a notable unconservative prediction. Due to this large bias in the simulation failure pressures toward higher pressures, we assumed that a mechanism driving failure or another aspect of the tests was missed in the original models. The goal of this work was to investigate potential sources of this bias focusing on geometric uncertainty and material model assumptions. As with the previous work, our simulations of the pipe bomb experiments using the BCJ material model over predicted the failure pressures. While success cannot be claimed for the simulated failure pressures, we believe we accurately identified the remaining sources of error in the simulations. Specifically, the temperature mapping algorithm and the geometry are believed to be the primary contributors to the errors. As a result, future work should focus on improving the temperature mapping algorithm and consider using temperature fields determined by a calibrated thermal model that includes convection. Additionally, CT scans of remaining portions of the pipe bomb material inner diameter should be taken to further understand the variability this unmachined surface introduced to the pipe bomb specimens.

42 ENGINEERING↗
DOE OSTI2018

Survey of DAKOTA's V&V Capabilities in the Simulation of Residual Stresses in a Simple Composite Structure

Process-induced residual stresses occur in composite structures composed of dissimilar materials. As these residual stresses can result in fracture, their consideration when designing composite parts is necessary. However, the experimental determination of residual stresses in prototype parts can be time and cost prohibitive. Alternatively, it is possible for computational tools to predict potential residual stresses. Therefore, a process modeling methodology was developed and implemented into Sandia National Laboratories' SIERRA/SolidMechanics code. This method can be used to predict the process-induced stresses in any composite structure, regardless of material composition or geometric complexity. However, to develop confidence in these predictions, they must be rigorously validated. Specifically, sensitivity studies should be completed to define which model parameters are critical to the residual stress predictions. Then, the uncertainty associated with those critical parameters should be quantified and processed through the model to develop stress-state predictions encompassing the most important sources of physical variability. Numerous sensitivity analysis and uncertainty quantification methods exist, each offering specific strengths and weaknesses. Therefore, the objective of this study is to compare the performance of several accepted sensitivity analysis and uncertainty quantification methods during the manufacturing process simulation of a composite structure. The examined methods include simple sampling techniques as well as more sophisticated surrogate approaches. The computational costs are assessed for each of the examined methods, and the results of the study indicate that the surrogate approaches are the most computationally efficient validation methods and are ideal for future residual stress investigations.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Verification and validation of residual stresses in composite structures

Process-induced residual stresses occur in composite structures composed of dissimilar materials. As these residual stresses could result in fracture, their consideration when designing composite parts is necessary. However, the experimental determination of residual stresses in prototype parts can be time and cost prohibitive. Alternatively, it is possible for computational tools to predict potential residual stresses. Therefore, the objectives of the presented work are to demonstrate an efficient method for simulating residual stresses in composite parts, as well as the potential value of statistical methods during analyses for which material properties are unknown. Specifically, a simplified residual stress modeling approach is implemented within Sandia National Laboratories’ SIERRA/SolidMechanics code. Concurrent with the model development, bi-material composite structures are designed and manufactured to exhibit significant residual stresses. Then, the presented modeling approach is rigorously verified and validated through simulations of the bi-material composite structures’ manufacturing processes, including a mesh convergence study, sensitivity analysis, and uncertainty quantification. The simulations’ final results show adequate agreement with the experimental measurements, indicating the validity of a simple modeling approach, as well as a necessity for the inclusion of material parameter uncertainty in the final residual stress predictions.

42 ENGINEERING↗
DOE OSTI2017

Validation and Verification of Multi-Material Split Rings

Process induced residual stresses commonly occur in composite structures composed of dissimilar materials. These residual stresses form due to differences in the composite materials coefficients of thermal expansion as well as the shrinkage upon cure exhibited by most thermoset polymer matrix materials. Depending upon the specific geometric details of the composite structure and the materials curing parameters, it is possible that these residual stresses can result in interlaminar delamination and fracture within the composite as well as plastic deformation in the structures metallic materials. It is important to consider potential residual stresses when designing composite parts and their manufacturing processes. However, the experimental determination of residual stresses in prototype parts can be prohibitive, both in terms of financial and temporal costs. As an alternative to physical measurement, it is possible for computational tools to be used to quantify potential residual stresses in composite prototype parts. A simplified method for simulating residual stresses was previously validated with two simple bi-material structures. Continuing on, the objective of this study is to further validate the simplified method for simulating residual stresses for bi-material split rings of different composites and layup variations. The validation process uses uncertainty quantification to develop a distribution of possible simulated residual stress states that are compared to experimentally measured residual stress states of fabricated structures similar to those simulated. The results of the comparisons indicate that the proposed finite element modeling approach is capable of accurately simulating the formation of residual stresses in composite structures and a temperature independent material model is adequate within the composites glassy region.

36 MATERIALS SCIENCE↗