Browsing by Subject "fracture mechanics"

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Design and Development of a Dual-Actuator Mixed-Mode Interaction Tester
(2018-05) Gandhi, Vatsa; Liechti, Kenneth; Huang, Rui
A dual-actuator system is designed and developed to test mixed-mode fracture of laminated beams. Material and geometric properties of silicon/epoxy interface was used to develop a failure envelope of energy release rates with respect to mode-mix. This failure envelope was then used to determine the critical moment, and load envelope. Beam theory analysis in and critical loads were used to obtain a failure envelope for displacements and end rotations. Failure envelopes were validated using finite element analysis in ABAQUS. Given critical load and displacement envelopes, load cells and actuators were selected and a loading device was manufactured. Labview was used to communicate with the actuator and to synchronize data acquisition of actuators, cameras, and load cells. Primary tests were conducted for polystyrene/PDMS interface under mode I loading conditions. Critical envelopes were validated experimentally and load-displacement curves were analyzed.
Estimating Strength of Lattice Structure Using Material Extrusion Based on Deposition Modeling and Fracture Mechanics
(University of Texas at Austin, 2017) Park, Sang-in; Watanabe, Narumi; Rosen, David W.
Geometrical complexity in lattice structures yields large bounding surfaces to be approximated during additive manufacturing (AM) processes. In material extrusion, approximation of geometries using finite-sized thin filaments introduces defects such as voids and gaps in as-fabricated geometries. This initiates cracks between layers and increases possibility of fracture by crack propagation. As a result, a lattice structure fabricated by material extrusion tends to fail at significantly lower stress than estimated strength without consideration of fracture mechanism. The goal of this research is to estimate strength of material extruded lattice structures considering bonding strength among layers. To achieve this, the bonding strength is determined based on a deposition process modeling scheme and fracture mechanics analysis. A two-layer deposition model is generated to investigate deposited geometry, and the effective interlayer-bonding strength is calculated using a cohesive zone model (CZM) and peel tests. The resulting strength is incorporated into the property-estimation procedure.
Fatigue Life Prediction of Additively Manufactured Metallic Materials Using a Fracture Mechanics Approach
(University of Texas at Austin, 2018) Torries, Brian; Shrestha, Rakish; Imandoust, Aidin; Shamsaei, Nima
The present study aims to model the fatigue strength of additively manufactured metallic materials employing a fracture mechanics approach. Specimens with different build orientations were subjected to strain controlled fatigue testing. Upon failure, the defect(s) responsible for crack initiation were identified by fractographic analysis. From these defects an equivalent internal defect size is calculated using the √𝑎r𝑒𝑎 method based on Murakami model. Using this parameter, the elastic-plastic energy release rate (𝛥𝐽𝐽𝑒𝑓𝑓) was determined, and the relationship between 𝛥𝐽𝑒𝑓𝑓 and fatigue life was investigated. The results showed that this method improves the predictability of the fatigue strength of additively manufactured materials when the defects size and location is known. The 𝛥𝐽𝑒𝑓𝑓 − 𝑁𝑓 relationship appeared to better fit the fatigue data of the experimental materials as compared to the 𝜀𝑎 − 𝑁𝑓 relationship and contributed to a reduction in data scatter.