Nondestructive assessment of pore size in foam-based hybrid composite material

Abstract

In situ nondestructive evaluation (NDE) during processing of high-temperature polymer-based hybrids offers great potential to gain close control of and achieve the desired level of pore size, with low overall development cost. During the polymer-curing cycle, close control over the evolution of volatiles would be beneficial to avoid the presence of pores or control of their sizes. Traditional NDE methods cannot realistically be expected to evaluate individual pores in such components as each pore evolves and grows during curing. However, NDE techniques offer the potential to detect and quantify the macroscopic response of many pores that are undesirable or intentionally introduced into these advanced materials. In this article, preliminary results will be presented for nondestructive assessment of pore size in foam-based hybrid composite materials using ultrasonic techniques. The ultrasonic method was chosen due to its high sensitivity to the change of composition in material, ability to provide the required depth of penetration and ability to provide the needed modulus information for the cured material through appropriate velocity measurements. Pore size was evaluated through the frequency content of ultrasonic signal. The effects of pore size on the attenuation of ultrasound were studied. Feasibility of this method was demonstrated on two types of foams with various pore sizes.