Characterization of Damage and Fracture Processes in Short Fiber BMC Composites by Acoustic Emission

Abstract

Acoustic emission (AE) and scanning electron microscope (SEM) techniques have been coupled with mechanical deformation to study the damage and fracture mechanisms in a short fiber BMC composite. During tensile deformation the initial damage process observed in the SEM was the formation of small cracks at filler particles and glass fibers. Damage due to this mechanism was identified with acoustic emission in the 40 dB amplitude range. Onset of this damage mechanism occurred at very low strains and damage continued to accumulate until fracture. At higher strains the small cracks were observed in the SEM to coalesce to form large cracks spanned by pulled-out fibers. Formation of the large cracks was identified with a burst of AE in the 70 dB amplitude range just prior to fracture. Crack growth during stress relaxation fracture or in single loading tests occurred in a discontinuous manner due to the fiber reinforcement.

A Novel “Fiber-Spacing” Model of Tensile Modulus Enhancement by Shortening Fibers to Sub-Millimeter in an Injection-Molded Glass Fiber Reinforced Polymer Bulk Molding Compound (GFRP-BMC)

“…Injection-molded glass fiber reinforced bulk molding compounds (GFRP-BMCs) are 3-phase systems consisting of polymer, fiber and ³30 to 55 mass% filler, 1,2) usually CaCO 3 . Glass fiber reinforcement usually ranges from 5 to 30 mass% while glass fiber length ranges from about 3.2 to 12.7 mm (1/8 to 1/2 in).…”

“…Glass fiber reinforcement usually ranges from 5 to 30 mass% while glass fiber length ranges from about 3.2 to 12.7 mm (1/8 to 1/2 in). 1,2) Formulations are optimized for precise dimensional control, flame resistance, high dielectric strength, corrosion and stain resistance, and color stability. BMCs are used for aerospace, automotive parts, housing for electrical wiring, and corrosion-resistant needs, hence mechanical property improvement is essential for durability and use life.…”

“…The masticated paste was then left to stand overnight with the rest of the pastes before injection molding and then injected molded into an ASTM D-638 family mold for dogbone-shaped specimens with a 3.03 © 10 5 N (75 ton) New Britain with the following processing parameters: mold temperature 436 K (163 C), barrel temperature RT, injection pressure 3.506.90 MPa, shot time, t s = ³2.0 s, hold time 15 s, and cure time 1.5 2.0 min. 1,2) Sample dimensions total length, gauge length, width, and thickness were ³210, 100, 12.6, 3.3 mm, respectively, with cross-sectional area of 42.0 mm 2 in the gauge length. Volume fractions, V f of the E-glass fibers, CaCO 3 filler, and polymers with remaining components were 0.1317, 0.2902 and 0.5781, respectively.…”

A “Mold Filling” Model from Viscosity Measurements in a Strengthened Injection-Molded Reduced Glass Fiber Length Polyester Bulk Molding Compound

“…The mixture was allowed to stand for several hours and then injected molded into an ASTM D-638 family mold for dog-bone shaped specimens 15) ( bers was measured to be 0.44 mm with a standard deviation of 0.203 mm by SEM. 1,2) In general, two standard deviations comprise approximately 95% of the population, which is 0.04 mm < l ber < 0.85 mm. Although nominal ber diameter, d was 14 μm, measurement by SEM mapping showed average d = 11.4 μm with standard deviation of +/−1.15 μm, thus 95% of the population was 9.1 < d < 13.7 μm.…”

“…GFRP-BMCs are 3-phase composite systems typically composed of short glass ber, polymer, and contain a high mass% of powder ller such as CaCO 3 . Glass ber reinforcement usually ranges from 5 to 30 mass% with nominal lengths of 3.2 to 12.7 mm (1/8 to 1/2 in), 1) and nominal diameters 14 μm.…”