Ability to determine the individual stresses photoelastically in orthotropic composites from isochromatic data, but without employing isoclinics or isopachics, is developed and demonstrated. This new capability is achieved by combining isochromatic information, complex stress functions and numerical nonlinear least-squares concepts into a new and effective hybrid method for stress analyzing composite materials. Unlike previous methods of photo-orthotropic-elasticity, the present technique simultaneously smoothes the recorded isochromatic data, provides reliable boundary information, and separates the isochromatics into individual stress components throughout the area of interest. The method is illustrated by evaluating the three individual stresses throughout a region adjacent to a hole in a uniaxially loaded orthotropic composite plate from the measured isochromatics.

A 16 spark-gap camera was used to record the dynamic photoelastic patterns of ten centrally cracked, Homalite-100 specimens which fractured under ten biaxial stress ratios ranging from 3.7 to 0.The dynamic photoelastic patterns of curved cracks were used to verify the previously developed dynamic crack curving criterion. Cracks, which immediately curved upon propagation in three specimens under high biaxial loadings, were used to verify the static counterpart of the dynamic crack curving criterion. A previously developed dynamic crack branching criterion was verified by the dynamic photoelastic results involving cracks which eventually branched under low biaxial loadings.,

ABSTRACT~In this paper, the isotropic and anisotropic photoelastic experimental hybrid methods for fracture mechanics are developed. Using the photoelastic experimental hybrid method, it is demonstrated that one can precisely obtain stress intensity factors and separate the stress components of isotropic and anisotropic plate problems from the only isochromatics.

The behaviors and stresses of an O-ring under uniform squeeze rates and internal pressure change with real time. Therefore, the behaviors and stresses of O-rings under uniform squeeze rates and internal pressures should be studied with real time. To achieve this, a loading device for a transparent type photoelastic experiment, through which various internal pressures and uniform squeeze rates are applied, was developed. The validity of the loading device in analyzing the behaviors and stresses of the O-ring under uniform squeeze rates and internal pressures with real time was verified. It was observed that the filling phenomenon of the O-ring into the space between the lower and front side occurred after forcing out continued for a duration of time. The study also indicated that maximum shear stress would be more effective as a fracture parameter than the maximum normal stress fracture criterion for an O-ring made from rubber.

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