Chiang Mai Journal of Science

     The deformation and distribution of force were investigated in different-sized rectangular shapes of polymethyl methacrylate (PMMA). The experiment involved inducing stress-strain on the surface of each sample based on a point loading of 688 N, followed by observation of the isochromatic fringe order and strain distribution using reflection photoelasti city. The samples were tested vertically between the clamps inducing the point loading. It was found that the fringe order and strain value depended on the sample size (different vertical heights and horizontal widths, with a constant thickness). The maximum strain and fringe order for the contact points on the samples decrease in the vertical direction from the contact point to the center and in a horizontal direction from the center to the edge of the sample. Based on a constant height and different widths of samples, the lowest width had the highest fringe order (4). Based on a constant width of the sample and different heights, the lowest sample height had the highest fringe order (5.5) and a microstrain value of 1,100. Therefore, the smaller the width or height of a sample, the greater the extent of deformation and distribution of force into the sample’s area.