Browsing by Author "Brake, Matthew"

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    A Comprehensive Data Set of CFRP Impact Damage Accumulation Through a Novel Impact Experimental Setup
    (2021-08-25) Pasupuleti, Shashank; Brake, Matthew
    In the following work, a low-velocity impact pendulum inspired by the Charpy and Izod testing impact pendulum was designed and manufactured to examine the in-plane strain response of IM7/8552-1 carbon fiber/epoxy composite specimens under the CFCF plate condition. The pendulum itself covers an impact energy range similar to the Charpy and Izod low-velocity impact testing setup, yet allow the pendulum to be applied to extended Tribology and Fracture Mechanics studies without a notched sample. Tensile tests were performed on six 16-ply composite samples to characterize the IM7/8552-1 composite within a comprehensive data set and to ensure that DIC as a non-contact strain measurement tool would suffice for impact testing. Impact tests were also performed at four different swing angles associated with four different impact energies. At each impact level, three 16-ply 2” x 1” samples per layup configuration were repeatedly struck at the same swing angle until the samples failed. In-plane strain plots of each impact sample’s rear surface were compiled for each sample through DIC in each direction: the longitudinal (x) direction parallel to the composite’s 0° fibers, the lateral (y) direction perpendicular to those fibers, and the shear strain associate with this plane. The results from the strain plots and collected force vs. time plots were utilized to investigate a critical impact energy, the discrepancy between the number of hits to failure each composite stacking sequence can endure, and patterns in the residual strain with each isolated hit at these distinct impact energies. These determinations are made to contribute to properly characterize composites in the framework of damage tolerance philosophy and “slow-growth” to enhance current composite damage modeling efforts in the pursuit of fatigue after impact.
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    A computational mechanics framework for modeling tribology experiments with friction and wear
    (2021-09-01) Lawal, Iyabo G; Brake, Matthew
    An interface is formed when a minimum of two parts are in contact. Loading of the interface occursat the contact patch, which ranges in dimension depending on the contact geometry. The contact patch is the apparent area of contact of the two surfaces; multiple contact patches may exist on a given interface. The input load on the interface can be grouped into two categories - static and dynamic. In the static case, the loads on the contact patch are known a priori and do not change with time. In the dynamic case, commonly observed in structural dynamics interfaces, the load at the interface varies dynamically. In both cases, the surface topology, and local material properties(Elastic Modulus, etc) of the interface change in response to several variables including: loading of the interface, geometry of the interface, and the density of the local contact patches in contact region. Recent experiments conducted at several Joint Mechanics summer research programs from 2015 through 2018, identified three main defects on interface subjected to structure level load inputs. The first defect, “fretting,” is a form of micro-slip at the interface caused by reciprocating tangential loading. “Fretting” looks like oxidized, rust-colored points on the interface and is the most visible surface defect. A second defect caused by high impact forces, is plastic damage at the subsurface of the interface, altering the local material behavior. A third effect also caused by high-cycle, reciprocating tangential loading of the interface, is wear debris generated at the contact patch on the interface. How defects affect structural response is an active area of research that requires understanding the complex interactions of material, loading and friction at several length scales. Motivated by observations from structural dynamics, the goal of this research is to quantify how material non-linearity and friction at the contact interface may explain observable defects present at the interface after tribology experiments. Using a computational mechanics frame-work, the FEM (Finite Element Method) is used to develop a model to show how the friction force and local material properties change in response to multi-directional, reciprocating loading on the contact interface. There are four main contributions of this work. The first is the development of an FEM based meso-scale model that captures the contact patch behavior subjected to fretting. The second is the development of the Elastoplastic Friction (EPF) framework to model different friction models and record the energy dissipation generated. This includes the four-parameter Bouc-Wen friction model which, prior to this study had not been used to modeling hysteric behavior of the contact interface. Its use allows the ability to model microslip within an FEM framework. In a third contribution, it was found that with wear, the contact stiffness at the contact interface corresponded to the structures’ stiffness response. And finally, the recognition that in structural dynamics, it is importance to match the structures’ interface slip range to a fretting rig with the same range of micro-slip, otherwise inaccurate structural response may ensue. The results of this study can provide insights about how to design interfaces and assemble structures to limit micro-slip. It also informs on existing jointed interface constitutive models. If integrated within existing structural dynamics FEM models, it has the potential to reduce overall uncertainty present in joint models of these systems.
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    Nonlinear modeling of structures with bolted joints: A comparison of two approaches based on a time-domain and frequency-domain solver
    (Elsevier, 2019) Lacayo, Robert; Pesaresi, Luca; Gross, Johann; Fochler, Daniel; Armand, Jason; Salles, Loic; Schwingshackl, Christoph; Allen, Matthew; Brake, Matthew
    Motivated by the current demands in high-performance structural analysis, and by a need to better model systems with localized nonlinearities, analysts have developed a number of different approaches for modeling and simulating the dynamics of a bolted-joint structure. However, it is still unclear which approach might be most effective for a given system or set of conditions. To better grasp their similarities and differences, this paper presents a numerical benchmark that assesses how well two diametrically differing joint modeling approaches – a time-domain whole-joint approach and a frequency-domain node-to-node approach – predict and simulate a mechanical joint. These approaches were applied to model the Brake-Reuß beam, a prismatic structure comprised of two beams with a bolted joint interface. The two approaches were validated first by updating the models to reproduce the nonlinear response for the first bending mode of an experimental Brake-Reuß beam. Afterwards, the tuned models were evaluated on their ability to predict the nonlinearity in the dynamic response for the second and third bending modes. The results show that the two joint modeling approaches perform about equally as well in simulating the Brake-Reuß beam. In addition, the exposition highlights improvements that were made in each method during the course of this work and reveal further challenges in advancing the state-of-the-art.
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    The effect of geometrical imperfections on the strength of OCTG
    (2018-02-12) Mutis Rueda, David; Stanciulescu, Ilinca; Brake, Matthew
    Oil Country Tubular Goods (OCTG) is a term used to describe the family of steel pipes that are used in the oil and gas industry for construction of wells and hydrocarbon production. The American Petroleum Institute (API) specifies the technical delivery conditions and requirements for OCTG. These requirements include material properties, dimensions, tolerances and allowable defects among others. The tolerances for dimensions and allowable geometrical defects are referred here as geometrical imperfections. This thesis focuses on the impact that these geometrical imperfections have on the strength of OCTG, which is a concern for both casing and tubing designers and tubular manufacturers. Eccentricity between the pipe outside and inside diameter, ovality of the pipe cross-section and lack of longitudinal straightness are the common geometrical imperfections included in the analysis, in addition to a particular case with internal surface wear caused by tool joint friction. The evaluation using the Finite Element Method (FEM) of pipes with and without the geometrical imperfections reveals that the theoretical calculations for onset of yield fail to capture the effect of imperfections under certain loading conditions. The eccentricity and lack of straightness impact the tension and compression strength while the ovality and internal surface wear impact the internal and external pressure strength. A high dependence of the onset of yield on the pipe geometry is identified and characterized in the post-processing of results. Finally, strength reduction factors that take into account the imperfection type, its magnitude, the loading conditions and relevant pipe geometry variables are proposed.