SBIR-STTR Award

This SBIR Phase I project investigates the feasibility of a novel strain gauge sensing residual strains in composites formed during the manufacturing process. Many factors lead to these residual strains such as poor mold designs, inappropriate temperature and pressure settings, unbalanced ply lay-up, uneven shrinkage of matrix and/or expansion of the fibers and differences in coefficient of thermal expansion between tooling and composite. Residual strains hamper the quality of composites products; the measurement of these strains will yield improved process and quality control. Quantum Magnetics is proposing a novel nondestructive strain sensor based on the principle of Nuclear Quadrupole Resonance (NQR). 1-5 wt% of crystalline additives is blended into the resin during fabrication of the composite structure. Composites will be manufactured with low and high residual strains via changes in manufacturing parameters and raw material variations. For measuring residual strains, the composite is irradiated with radio frequencies to evoke an NQR response from the embedded crystals, which is a function of strain. The Phase I objectives are: (1) determine relevant NQR characteristics of additive in composite, (2) investigate shift of the NQR frequency as a function of residual strain and (3) develop a preliminary design for a Phase II prototype.

This Small Business Innovation Research (SBIR) Phase II project will develop a novel non-contact strain sensor for quality control in production of polymers and fiber-reinforced composites. By measuring residual strains, good parts can be distinguished from bad parts in the production stream. Internal and surface residual strains will be measured by a strain gauge based on the principle of nuclear quadrupole resonance (NQR). A small percentage of tiny additive crystals are blended into the resin during fabrication of the composite. For strain measurement, the composite is irradiated with radio frequencies (RF) to evoke a strain-dependent NQR response from the embedded crystals. Phase I manufactured parts with embedded additive via compression molding. Phase II will build a single-sided strain prototype and measure residual strains in pultruded parts. The NQR-active additive will be introduced into the pultrusion process, and several batches of different types of composites, e.g., fiberglass, will be manufactured. Pultrusion will permit several large batches of samples to obtain the statistics needed to refine the NQR-based quality control method. Potential commercial applications are expected in many industries, such as civil infrastructure, automotive, sporting goods, aerospace, and many others utilizing composite materials.