Search Results

In the Army mechanical fatigue subject to external and inertia transient loads in the service life of mechanical systems often leads to a structural failure due to accumulated damage. Structural durability analysis that predicts the fatigue life of mechanical components subject to dynamic stresses and strains is a compute intensive multidisciplinary simulation process, since it requires the integration of several computer-aided engineering tools and considerable data communication and computation. Uncertainties in geometric dimensions due to manufacturing tolerances cause the indeterministic nature of the fatigue life of a mechanical component.

A continuation of the SAEFDE round-robin fatigue test program was conducted to determine the influence of a finer microstructure on monotonic tension, strain-controlled low cycle fatigue, fatigue crack growth, and fracture toughness of A356-T6 cast aluminum alloy. The finer microstructure castings, referred to as material W, were obtained using a water-chilled sand casting procedure. Material W exhibited more desirable ductile behavior than the previous SAEFDE materials X, Y, and Z. Material W exhibited superior smooth specimen low cycle fatigue resistance at both short and long lives, when compared to materials X, Y, and Z. This was due in part to the higher ductility and lower porosity of material W over materials X, Y, and Z. Material W exhibited similar fatigue crack growth behavior, and slightly higher values of fracture toughness at the same thickness when compared to materials X, Y, and Z.

Fracture toughness tests were conducted on the SAEFDE Committee's round-robin A356-T6 cast aluminum alloy materials designated X, Y and Z. Compact type specimens with a thickness of 9.1 and 20.3 mm were tested. Valid Klc values couid not be obtained for 9.1 mm thick specimens but were obtained for 20.3 mm thickness specimens. Due to larger castings, and hence slower cooling rates, a coarse secondary dendrite arm spacing, DAS, of 80 to 90 μm existed in the three materials. Similar Klc values were 18, 16.7 and 17.3 for the A356-T6 materials X, Y and Z respectively. Final fracture surfaces were also similar with predominant cleavage fracture with some localized ductile dimples and secondary cracking.

This paper presents an optimization-based algorithm for simulating the dynamic motion of a digital human. We also formulate the metabolic energy expenditure during the motion, which is calculated within our algorithm. This algorithm is implemented and applied to Santos™, an avatar developed at The University of Iowa. Santos™ is a part of a virtual environment for conducting digital human analysis consisting of posture prediction, motion prediction, and physiology studies. This paper demonstrates our dynamic motion algorithm within the Santos™ virtual environment. Mathematical evaluations of human performance are essential to any effort to compare various ergonomic designs. In fact, the human factors design process can be formulated as an optimization problem that maximizes human performance. In particular, an optimal design must be found while taking into consideration the effects of different motions and hand loads corresponding to a number of tasks.

This paper presents a summary of recently developed unified method of continum design sensitivity analysis of linear and nonlinear structural systems. Sizing design variables, such as thickness and cross sectional areas, and shape design variables, such as length and geometric shape, of structural components of built-up structures are considered. For design sensitivity analysis of nonlinear structures, both geometric and material nonlinearities are considered using the total and updated Lagrangian formulations. For sizing design variables, a distributed parameter structural design sensitivity analysis approach that retains the continum elasticity formulation throughout the derivation of design sensitivity analysis results is used. For shape design variables, the material derivative concept of continuum mechanics is used to relate variations in structural shape to measures of structural performance.

Reliability-based design optimization (RBDO), which includes design optimization in design space and inverse reliability analysis in standard normal space, has been recently developed under the assumption that all input variables are independent because it is difficult to construct a joint probability distribution function (PDF) of input variables with limited data such as the marginal PDF and covariance matrix. However, since in real applications, it is common that some of the input variables are correlated, the RBDO results might contain a significant error if the correlation between input variables for RBDO is not considered. In this paper, Rosenblatt and Nataf transformations, which are the most representative transformation methods and have been widely used in the reliability analysis, have been studied and compared in terms of applicability to RBDO with correlated input variables.

A robust design procedure is applied to achieve improved vehicle handling performance as an integral part of simulation-based vehicle design. This paper presents a hybrid robust design method, the robust design process strategy (RDPS), which makes full use of the intense complementary action of characteristics between the Response Surface Methodology (RSM) and the Taguchi method, to get the robust design of the vehicle handling performance. The vehicle multi-body dynamic model is built in the platform that is constructed by the software of iSIGHT, ADAMS/CAR, and MATLAB. The design-of-experiment method of the Latin Hypercube (LHC) is used to obtain the approximate area values, and then the RDPS is utilized to achieve improved vehicle handling performance results. The validation is made by the Monte Carlo Simulation Technique (MCST) in terms of the effectiveness of the RDPS in solving robust design problems.