Nathan A. Mauntler

Comparison Between Elastic Foundation and Contact Force Models in Wear Analysis of Planar Multibody System

In this paper, two procedures to analyze planar multibody systems experiencing wear at a revolute joint are compared. In both procedures, the revolute joint of interest includes a clearance whose shape and size are dictated by wear. The procedures consist of coupled iterative analyses between a dynamic system analysis with nonideal joints and a wear prediction to determine the evolution of the joint clearance. In the first procedure, joint forces and contact pressures are estimated using the elastic foundation model with hysteresis damping via the dynamic analysis. In the second procedure, a contact force model with hysteresis damping is used to estimate the joint forces. In the latter case, however, the contact pressure is estimated using a finite element method (FEM). A comparison in performance of the two models is facilitated through the use of an experimental slider-crank mechanism in which wear is permitted to occur at one of the joints. It is observed that the two procedures provide similar estimates for the dynamic response and wear volumes but substantially different predictions on the wear profiles. Additionally, experimental results show that while predictions on the wear volume from both models are reasonably accurate, the FEM-based model produced more accurate predictions on the wear profile.

Metallic Glass Surface Patterning by Micro-Molding

The micro-molding of bulk amorphous metal to create sub-micrometer to sub-millimeter surface features was investigated. The goal was to demonstrate the reproduction of such features in a metallic material from a master. The bulk metallic glass material was embossed between the glass transition and crystallization temperatures. Silicon wafers patterned by deep reactive ion etching were used as masters. The patterns were designed to test the effects and interactions of aspect ratios, geometry, and spatial proximity. In addition to these patterns, a master was developed to mold two-dimensional channel geometries. Comparisons between the replicated features and the molds are provided.Copyright

Modeling a Slider-Crank Mechanism With Joint Wear

The paper presents a study on the prediction of wear for systems in which progressive wear affects the operating conditions responsible for the wear. A simple slidercrank mechanism with wear occurring at one of the joints is used to facilitate the study. For the mentioned mechanism, the joint reaction force responsible for the wear is, itself, affected by the progression of wear. It is postulated that the system dynamics and the wear are coupled and evolved simultaneously. The study involves integrating a dynamic model of the slider-crank mechanism (with an imperfect joint) into a wear prediction procedure. The prediction procedure builds upon a widely used iterative wear scheme. The accuracy of the predictions is validated using results from an actual slider-crank mechanism.

Dynamic Modeling of a Slider-Crank Mechanism Under Joint Wear

A study of how joint wear affects the kinematics of a simple slider-crank mechanism and in turn how change in kinematics of the mechanism affects the joint wear is presented. The coupling between joint wear and system kinematics is modeled by integrating a wear prediction process, built upon a widely used finite-element-based iterative scheme, with the dynamic model that has an imperfect joint whose kinematics changes progressively according to joint wear. Three different modeling techniques are presented based on different assumptions, and their performances are compared in terms of joint forces and wear depths. It turns out that the joint wear increases the joint force and accelerates the wear progress. The accuracy of integrated dynamic model is validated by measuring joint force and wear depth of the slider-crank mechanism. Details of instrumentation are also presented.Copyright

The Influence of Process Variation on a Cortical Bone Interference Fit Pin Connection

The interference fit is a common method for creating mechanical assemblies. When manufacturing the individual components to be assembled in this method, close dimensional control of the mating components is required in order to ensure that the amount of interference is sufficient to create a secure assembly, but not so great as to cause excessive stresses or failure of the individual components. In this work, we study interference fit connections in an assembly of human (cadaveric) cortical and cancellous bone, i.e., an allograft, used in spinal fusion surgeries. A difficulty encountered in this application is that, in addition to the machining steps, the assembly must go through subsequent sterilization and lyophilization, or freeze drying, processes that may affect the quality of the interference fit. This report examines the quality of the allograft interference fits using dimensional measurements of manufactured components at all stages of the manufacturing process, followed by examination for cracking and measurement of the pull-apart forces for assemblies. The experimental results are compared to finite element models of the interference fit and also to Monte Carlo models of the assembly using a simple thick-wall cylinder model. Experimental results show that the lyophilization process significantly affects the component dimensions, resulting in a much greater spread in interference values and likely leading to cracking and/or loss of interference.