Fundamental study of dynamic stress wave using a dynamic photoelastic method

Experiments have been conducted to investigate a fundamental relationship between stress waves and photoelastic fringes under condition of applied impact pulse loads to testing objects. The testing objects are made of DAP plastic plates with 15,30,45,60 and 90 mm of width. Impact stresses were applied to the one side of the plates by air-gun. The stress wave propagation speed was determined by observation of photoelastic fringes in the test pieces. The fringe position was determined by means of image processing technique and the photoelastic data were compared with those obtained by the measured impact pulse wave forming with strain gauges under the same conditions to raise the reliability of photoelastic measurement. The impact stress wave propagation speed decreased with a distance from the initial loading point, and took a minimum at a distance of about 1.2 times of plate width, then it increased and became constant at a distance of over 2 or 3 times of plate width. For the test piece with smallest width, 15mm, the constant wave speed was approximately equal to the theoretical ones calculated for a thin rod. For the other test pieces, the constant wave speed decreased with increase of the plate width and they were different from any theoretical values for a thin rod and an infinite flat plate.