John Lasecki

Statistical Approaches Applied to Fatigue Test Data Analysis

The use of statistics is an important aspect in the analysis of fatigue test results. This paper describes the use of the Maximum Likelihood Estimate to analyze the fatigue results of staircase tests and Life-Regression Models (S-N curve). Two life-regression models are analyzed: a modified Basquin model and the Random Fatigue Limit (RFL) model.

Evaluation of Fiber Orientation Prediction of Moldflow Using an Injection Molded IP Panel

The fiber orientation distribution is one of the important microstructural variables for thermoplastic composites reinforced with discontinuous fibers. In this article, Moldflow is used to predict the fiber orientation distribution in an automotive component. Image analysis by MATLAB is adopted to validate the simulated results after taking pictures of fibers by X-ray CT. It is shown that the Moldflow predicts the average distribution in direction of the thickness accurately, with predicted eigenvalue of the orientation tensor within 5% of that measured. However, it failed to capture the change of principal eigenvalue in thickness direction.Copyright

Development and Validation of CFD Methodology to Simulate Water Quenching Process

A computer simulation methodology is developed to model the water quenching process for engine block and cylinder head. The methodology is based on the Eulerian-Eulerian two-fluid method implemented in existing commercial computational fluid dynamics (CFD) software. Due to the complex physics involved in the phase change and mass transfer, one of the prime objectives is to search and evaluate CFD tools that are capable of modeling the water quenching processes. Then the methodology is validated by comparing the CFD result with thermocouple data from lab experiments conducted in a controlled environment. Thorough comparison of results from various quench orientations indicated that the methodology is robust enough to produce reasonable and consistent results. The temperature history obtained by this methodology could be mapped to FEA model to predict residual stress, which in turn can be used to study the durability of the engine components.Copyright

Fatigue and Fretting of Mixed Metal Self-Piercing Riveted Joint

The fatigue behavior of self-piercing riveting (SPR) joint, joining aluminum alloy 6111T4 and steel HSLA340 sheets with lapshear geometry was investigated in this paper. Sheet crack was the dominant failure mode, while unexpected rivet shank failure tended to occur under high loading level. Fretting wear was observed at interface of aluminum and steel layers, as well as at rivet and sheets under sinusoidal cyclic tension-tension loading. An energy dispersive X-ray (EDX) analysis of fretting debris revealed the presence of oxide of aluminum and zinc. Fretting was shown to be critical as crack initiation spot. In sheet failure mode, micro cracks were found to initiate at early stage, and crack initiation life was much shorter than crack growth life.Copyright