Elastic Modulus Measurements

Laser-ultrasound measurement of elastic modulus is based on the acoustoelastic effect - the dependence of the propagation velocity of ultrasonic waves on the stresses in the investigated medium. Local elastic modulus can be calculated with from known density and measured velocities of longitudinal and shear ultrasonic waves in the case of one-sided access to investigated object by using transducer with pitch-catch configuration (PLU-6N-02). The short duration and high quality of laser excited ultrasonic pulses make it possible to measure the velocity of ultrasonic waves with precision accuracy on a small basis (the statistical spread of measurements exceeds 5x10-4 with a path length more than 2 mm. The relative accuracy of measuring the velocity of a longitudinal ultrasonic wave in the range 4-10 mm/μs is no worse than 1% at a base of 30 mm.

The small dimensions of the laser-ultrasonic beam (2 mm) allow the local measurement of the velocity of the longitudinal and shear waves simultaneously. According to the velocity and density of the material, a complete set of material elastic modules (Young's modulus, shear modulus, Poisson's ratio) is calculated locally. Relative accuracy is better than 2%.

The results of laser ultrasonic measurements of elastic modulus of experimental torsion boxes during static stress tests are presented below.