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Browsing by Subject "finite element analysis"

Now showing 1 - 3 of 3
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    Development Of A Silicone Mold Tool For Injection Molding Plastic Parts
    (2020-05) Tahir, Irfan
    Injection molding is one of the most popular processing methods for manufacturing plastic parts. Typically, injection mold tools are made out of metal. The design and development of these metallic mold tools is a very expensive and lengthy process which means that it is difficult to incorporate this process into the prototyping stage of a product. Currently, the most widely researched method used for rapid prototyping of injection mold tools is additive manufacturing (AM). This project investigates an alternative to AM as a rapid prototyping method by investigating a cost-effective mold tool made out of silicone. A robust step by step process of creating a silicone mold tool is presented. To determine the right plastic to inject into the silicone mold tool, an injection molding simulation is conducted comparing three types of plastics and their effect on the filling of the mold tool. Following the simulation, Design of Experiment (DOE) is used to measure the main and interaction effects of the silicone mold tool’s durometer hardness, geometry, and design complexity on its performance. Additional DOE studies were conducted to optimize the injection molding processing parameters for fabricating ASTM D638 Type IV tensile specimens. From the experiments, it was found that a durometer of Shore A Hardness 40 is the most optimum value for a silicone mold tool. Durometers smaller than that increase the likelihood of failure by flash and durometers larger than that damage the mold tool through brittle failure. Design changes were made to the mold tool geometry to use 3D printed inserts and shorten the length of the runner, the latter of which resulted in ideal samples without any failures. Comparison of mechanical properties of the silicone mold test coupons with those produced using a metallic mold tool revealed that there was a 7.3% decrease in Ultimate Tensile Strength when going from metal to silicone mold tool, better than those previously reported for some AM mold tools. In conclusion, the silicone mold tool is a promising alternative to AM mold tools for rapid prototyping of injection molded parts with certain limitations.
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    Failure Mechanics of Nonlinear, Heterogeneous, Anisotropic Cardiovascular Tissues: Implications for Ascending Thoracic Aortic Aneurysms
    (2019-06) Korenczuk, Christopher E.
    Characterizing the mechanical response and failure mechanisms of cardiovascular tissues is critically important, as these tissues play a vital role in the native functioning of the body. In the case of pathological events, such as aortic aneurysms or myocardial infarctions, mechanical behavior can be altered due to adverse remodeling, and thus affect the integrity of the tissue. Ascending thoracic aortic aneurysms (ATAAs) occur when the aorta enlarges beyond its normal diameter, and dilation is typically accompanied by disorganization of the underlying aortic fibrous structure. Current diagnostic methods depend solely on measuring aneurysm diameter, neglecting considerations of mechanical strength, which results in an inefficient risk assessment. To better understand the failure mechanism of ATAAs, the work presented here used a combination of experimental testing and computational modeling to characterize failure in human ATAA tissue. Experimental testing showed that ATAA tissue exhibited significantly lower mechanical strength when compared to healthy porcine tissue in multiple loading configurations. Furthermore, experimental tests highlighted the large disparity between uniaxial and shear strength in ATAA tissue, where the tissue was substantially weaker in shear loading conditions. A custom multiscale finite-element model was then used to interrogate fiber failure more closely in both experimental loading conditions, and inflation of a patient-specific ATAA geometry. Modeling results showed that fibers between the lamellar layers of the aortic wall failed significantly more than fibers within the planar layers in shear loading conditions, as well as during inflation of the patient-specific geometry. Taken together, these results suggest that intramural shear could be an important contributor to the failure or dissection of ATAAs.
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    Numerical Modeling of Stress Corrosion Cracking in Polymers
    (2015-12) Ge, Hanxiao
    Polymeric materials have been increasingly used for structural purposes in civil infrastructures. However, stress corrosion cracking has been a critical issue that affects the service lifetime of polymer components. My preliminary study showed that polyethylene may be severely corroded in an oxidizing environment and lose its fracture resistance property. Experimental methods have been primarily adopted to investigate stress corrosion cracking in polymers; however, these approaches are expensive to apply, and may fail to account for certain aspects of this chemo-mechanical process. Therefore, a numerical approach is needed to investigate this issue. A unified chemo-mechanical model is developed to predict the stress corrosion cracking (SCC) of a viscoplastic polymer. This model is applied to the specific case of high density polyethylene (HDPE) exposed to a chlorinated environment at a constant stress load. This chemo-mechanical model is comprised of three components, each capturing a critical aspect of SCC. An elastic-viscoplastic constitutive model is adopted to predict the time-dependent creep behavior of HDPE, and the model parameters have been calibrated through tensile testing. This constitutive model has been implemented in finite element analysis by using a user-defined material subroutine. The polymer fracture property is considered to be dependent on the extent of corrosion, and this dependence is implemented with a cohesive zone model. A chemical kinetics and diffusion model is utilized to predict the degradation of fracture properties in the material as a result of reactions and migration of chemical substances. The coupled chemo-mechanical simulation is accomplished by integrating the chemical reaction calculation into finite element analysis via user defined subroutines. Two modes are considered for failure of the polymer: excessive plastic deformation or catastrophic unstable crack growth. At high stresses, the failure is primarily due to excessive plastic deformation. At low stresses, chemical reactions and diffusion are the dominant factors leading to failure. In addition, two distinct patterns of crack growth (reaction-driven or diffusion-driven) are revealed at various disinfectant concentrations at low stress levels. In reaction-driven crack growth, material degradation is localized at the crack tip, and crack growth rate is a constant throughout the simulated lifetime. However, when diffusion dominates, the entire specimen ligament may be severely degraded, and crack growth accelerates at the end of component lifetime. The current simulation framework allows exploring the interaction of various factors in stress corrosion cracking, such as disinfectant concentration, loading, and temperature. The framework is also general enough to be implemented for other polymeric materials and corresponding corrosion mechanisms. In the future, the proposed chemo-mechanical modeling approach may be expanded to analyze the performance of a variety of materials under stress corrosion cracking. In addition, a stochastic methodology may be incorporated to account for the variances in loading, as well as material properties.