Crack Onset in PMMA Plates with Circular Holes by Finite Fracture Mechanics
Crack onset in Polymethyl Methacrylate (PMMA) holed plates, subjected to tensilestress, has been studied through the application of a Coupled stress and energy Crite-rion in the framework of the Finite Fracture Mechanics (CC-FFM). Different hole sizeswere tested and an expected hole size effect was...
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| Format: | doctoral thesis |
| Status: | Published version |
| Publication Date: | 2021 |
| Country: | España |
| Institution: | Universidad de Sevilla (US) |
| Repository: | idUS. Depósito de Investigación de la Universidad de Sevilla |
| OAI Identifier: | oai:idus.us.es:11441/131441 |
| Online Access: | https://hdl.handle.net/11441/131441 |
| Access Level: | Open access |
| Keyword: | Finite Fracture Mechanics Coupled Criterion Crack onse PMMA Plates with holes in tension Non-linear Elastic material law Linear Viscoelastic ma-terial law Mecánica de la Fractura Finita criterio acoplado iniciación de fisura placas con agujeros sometidas a tracción Ley de Comportamiento No Lineal Elástica Ley de Comportamiento Lineal Viscoelástica |
| Summary: | Crack onset in Polymethyl Methacrylate (PMMA) holed plates, subjected to tensilestress, has been studied through the application of a Coupled stress and energy Crite-rion in the framework of the Finite Fracture Mechanics (CC-FFM). Different hole sizeswere tested and an expected hole size effect was observed. PMMA was tested accordingto standard procedures to obtain its elastic, viscoelastic and fracture properties.The CC-FFM was developed and implemented for several material behaviour lawsin the commercial Finite Element (FEM) code ANSYS and MATLAB, apart from theLinear Elastic one, also Non-linear Elastic and Linear Viscoelastic.A semi-analytic Linear Elastic model was obtained by using Kirsch’s formula for thecase of an infinite holed plate in tension. For finite holed plates a numerical Linear Elas-tic model and a Non-linear Elastic model, via Ramberg-Osgood approximation, weredeveloped as well. Finally, a Linear Viscoelastic model was obtained numerically viaProny series based on tensile tests performed at different strain rates. The plane stressand strain effects were considered in the present studies.Three point bending tests, flatwise and edgewise, using plain coupons (without anynotch), were carried out at different velocities. The bending strength was higher than thatobtained in the tensile tests. FEM models of those bending tests were also developedincluding the different material laws. For the Non-linear case, the Ramberg-Osgoodapproximation was either based in tensile and bending tests.A new strength value was obtained for PMMA, for each material model apart fromthe Linear one, by introducing in ANSYS the average critical test load from three pointbending tests, for the material models based in tension tests.Finally, an inverse procedure was performed, using CC-FFM, to determine the strengthand fracture properties of the material. The idea is to obtain cGccurves for severaldiameters, and their intersections will yield estimated strength and fracture material val-ues. All the three models predicted a size effect in holed specimens, although only verymoderate size effect was predicted in general by the Non-linear Elastic model. Thepredictions by the Coupled Criterion of FFM gave better predictions in the Linear Vis-coelastic case, when compared to experimental results. The Non-linear Elastic modelalso gave better predictions than the Linear Elastic model case. The assumption of anincreased strength value, justified by a random distribution of material flaws, was ofmost importance in those predictions. |
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