Assembled mechanical systems often contain a large number of bolted connections. These bolted connections (joints) are integral aspects of the load path for structural dynamics, and, consequently, are paramount for calculating a structure's stiffness and energy dissipation prop- erties. However, analysts have not found the optimal method to model appropriately these bolted joints. The complexity of the screw geometry cause issues when generating a mesh of the model. This paper will explore different approaches to model a screw-substrate connec- tion. Model parameters such as mesh continuity, node alignment, wedge angles, and thread to body element size ratios are examined. The results of this study will give analysts a better understanding of the influences of these parameters and will aide in finding the optimal method to model bolted connections.
There are numerous scenarios where critical systems could be subject to penetration by projectiles or fixed objects (e.g., collision, natural disaster, act of terrorism, etc.). It is desired to use computational models to examine these scenarios and make risk-informed decisions; however, modeling of material failure is an active area of research, and new models must be validated with experimental data. The purpose of this report is to document the experimental work performed from FY07 through FY08 on the Campaign Six Plate Puncture project. The goal of this project was to acquire experimental data on the puncture and penetration of metal plates for use in model validation. Of particular interest is the PLH failure model also known as the multilinear line segment model. A significant amount of data that will be useful for the verification and validation of computational models of ductile failure were collected during this project were collected and documented herein; however, much more work remains to be performed, collecting additional experimental data that will further the task of model verification.
In order to predict blast damage on structures, it is current industry practice to decouple shock calculations from computational structural dynamics calculations. Pressure-time histories from experimental tests were used to assess computational models developed using a shock physics code (CTH) and a structural dynamics code (PRONTO3D). CTH was shown to be able to reproduce three independent characteristics of a blast wave: arrival time, peak overpressure, and decay time. Excellent agreement was achieved for early times, where the rigid wall assumptions used in the model analysis were valid. A one-way coupling was performed for this blast-structure interaction problem by taking the pressure-time history from the shock physics simulation and applying it to the structure at the corresponding locations in the PRONTO3D simulation to capture the structural deformation. In general, the one-way coupling was shown to be a cost-effective means of predicting the structural response when the time duration of the load was less than the response time of the structure. Therefore, the computational models were successfully evaluated for the internal blast problems studied herein.
Sandia National Laboratories has developed a new technique for testing in a combined linear acceleration and vibration environment. Amplified piezo-electric actuator assemblies are used in combination with Sandia's 29-ft centrifuge facility to surpass the load capabilities of previous attempts using traditional mechanical shaker systems. The piezoelectric actuators are lightweight, modular and overcome several limitations presented by a mechanical shaker. They are 'scalable', that is, adding more piezo-electric units in parallel or in series can support larger-weight test articles or wider range of displacement/frequency regimes. In addition, the units could be mounted on the centrifuge arm in various configurations to provide a variety of input directions. The design along with test results will be presented to demonstrate the capabilities of the new piezo-electric Vibrafuge.