3D-FE analysis of soft liner-acrylic interfaces under shear loading.

Aim: To analyze the distribution of stresses at the bond interface of Molloplast-B soft-liner attached to PMMA acrylic surface of different geometries (smooth and rough) and at different load-application distances by 3D-FEA modeling of typical shear-bond test. Methodology Three-dimensional finite element analysis (3D-FE) was performed utilizing Patran and Marc softwares (MSC.Software, USA). Models of Molloplast-B disk liner (diameter: 8mm, thickness: 3mm) bonded to smooth and rough acrylic geometries were designed. A total of 8 models (4 models for each surface geometry) were used to analyze Von Mises, maximum principal and shear stresses for the nodes corresponding to the vertical diameter of the acrylic-liner interface when applying a uniform shear-loading at different distances from the interface; 0.25, 0.5, 1, and 2mm. Materials properties were assumed to be isotropic, homogeneous, linear and elastic.

Results: Shear loadings, at various distances from the bond-interfaces, produced different magnitudes of shear and tensile stresses. They were more uniform for both smooth and rough geometries when loading was applied at smaller distances from the interface (0.25 and 0.50). The maximum shear stress did not surpass maximum tensile stress in the areas subjected to the highest stress. These values were higher for the models with increased distances and bending moment associated with rough surfaces.

Conclusions: It can be concluded that in conducting shear bond tests, shear and tensile stresses are present regardless of the distance from the bond interface at which the shearing stress is applied. However, at increased distances from the bond interface, tensile stresses are greater than shear stresses. When shear stress is applied at shorter distances from the bond interface (0.25 or 0.50mm), and regardless of bond-interface geometry; there is more uniform stress distribution and lower effect of bending moment. However, in vitro studies of bond strengths between soft liners and acrylic substrates obtained by shear test should be approached with caution, considering the distance of load application and the surface treatment of the substrate as the most important factors that could interfere with the shear test values.