UC San Diego

The increased used of complex geometries in aerospace and automotive applications has been possible due to recent advancements in material manufacturing methods. Materials such as woven polymer matrix composites and additively manufactured (AM) metals offer benefits in weight and part reduction compared to traditional aerospace materials. The need for the experimental and numerical characterization of the nonlinear behavior in advanced composites and defects in laser powder bed fusion (LPBF) metals under intermediate loading rate is needed to better use such materials in aerospace and automotive applications which are subjected to impact or crash events. The establishment of comprehensive material databases is both labor intensive and costly. The need for an efficient methodology to characterize the rate-dependent behavior is therefore needed.

To address this problem, experimental characterization of the in-plane shear response of two balanced plain weave carbon fiber composites is studied using test methods based on a v-notch shear specimen and a shear fixture designed using a combination of the ASTM D7078M and a modified Arcan fixture. Additionally, specimen preparation for digital image correlation (DIC) with Phantom high speed cameras is discussed. Results from 2D DIC and measured force values are used to obtain experimental stress-strain curves. Comparison between quasi-static and intermediate rates mechanical behavior show increase in strength and modulus for both plain weave carbon fabrics.

Additionally, a hybrid experimental and numerical characterization methodology is developed for woven polymer matrix composites that uses models from Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) with experimental stress-strain curves. Validation of this methodology is performed through coupon verification in finite element analysis (FEA) software LS-DYNA for two woven materials using a tabular plasticity material model, MAT213. Additionally, validation studies of an adhesively bonded composite wingbox structure subjected low velocity impact is simulated and compared with experimental tests.

Lastly, experimental investigation of the combined effects of heat treatment on AM steel metals with fusion defects is performed through uniaxial tension experiments at various loading rates. High-speed camera images of mechanical tests seek to determine how heat treatment affects the material response and failure. Optical microscopy images are used to observe the failure mechanisms of specimens with internal defects.