Browsing by Author "Brake, Matthew R. W."
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Item A New Tool for Investigating Mesoscale Contact(2020-04-16) Despard, Tyler Tyler; Brake, Matthew R. W.This thesis presents a body of work undertaken to develop a new contact test rig for the Tribomechadynamics Lab. Motivated by a continued interest in the design and modeling of joined structures, the need for a mesoscale contact testing capability is uncovered by a discussion of several research areas. Built upon the science of instrumented indentation, the test rig is capable of a maximum applied load of 4,000 N over a contact displacement of less than 90 microns. Resolution in the load - displacement data is 2 N and 100 nm, respectively. Interchangeable contact tips and a custom built height positioning stage contribute to the flexibility of the tool. The accompanying controller and user interface allow for high test throughput by even inexperienced users. The construction, validation, and initial testing of the rig are described in depth. The development of the post-processing methods and derivation of several material properties from the load-displacement data are covered as well. The functionality of the rig is illustrated by the results of three unique applications: an indentation and flattening study on multiple materials, a study of the influence of coating thickness on the properties of layered solids, and a proof of concept for a future rough contact study. Data from high fidelity surface characterization is integrated with the contact data. A tool for maximizing productivity and capability by stitching surface scans into a complete surface of interest is developed as well. The promising results of the initial testing motivates a discussion of future additions to the rig and applications not yet explored.Item Multi-Scale Modeling in Bolted Interfaces(2019-08-06) Balaji, Nidish Narayanaa; Brake, Matthew R. W.The thesis develops a framework for modeling the dynamics of bolted structures in a multi-scale manner. Understanding that most of the challenges faced by the joints community is around the reconciliation of contact response with physical parameters of the system, the current work is an attempt for this reconciliation using properties identified from interfacial scans of the structure. The basic idea of statistical averaging as conducted in rough contact studies is used here for achieving this in a segment-by-segment fashion. Thus, the response characterization may be done in a manner that represents the micro-level asperity distributions while also preserving a meso-level understanding of possible local variations. Since all of these are used, through the framework, for macro-level simulations of the dynamics, the approach links the micro-, meso-, and the macro-length scales (in that order). For the dynamical simulations, a modified modal quasi-static approach is proposed, which is capable of representing amplitude-dependent nonlinear modal characteristics of nonlinear dynamical systems with linear limit cases. Since the fully stuck and the fully slipped cases may be taken as the limit cases, this is well applicable for the cases with frictional contacts. The results for the modified approach are compared with the responses characterized from other time- and frequency-domain approaches for a simple example in order to validate its efficacy. Finally, the approach is applied for a three bolt lap-joint benchmark (the so-called ``Brake-Reu{\ss}-Beam''). Since the characterization of the interface is conducted in a full-field manner on top of a finite element mesh, the framework is also demonstrated to be applicable for conducting full-field micro-scale interface evolution studies. Validating this would enable models with backward-evolutionary dependence (macro- influencing meso- influencing micro-scale attributes). To this end, preliminary statistical studies are conducted to establish and/or understand correlations of local changes in relevant roughness parameters with predicted local tractions and dissipation fluxes.