Tensile Strength Enhancement by Shortening Glass Fibers with Sub-Millimeter Length in Bulk Molding Polymer Compound

Abstract

Effects of short fiber with sub-millimeter length on tensile strain, " f and tensile strength, f were investigated for a bulk molding compound (BMC) glass fiber reinforced polymer (GFRP) composite with 20 mass% E-short glass fibers. The " f and f values of BMC-GFRP samples with 0.44 mm short fibers were almost 40 and 60% higher than that of BMC-GFRP samples with long fibers (3.2 and 6.4 mm in length), as well as more than 65 and 110% higher than that of the filled fiber free resin, respectively. The reduced fracture strain (" f =" f,6.4 ) and reduced tensile strength ( f = f,6.4 ) as a function of the fiber end density, E (cm À3 ) were expressed by the following equations with linear regression as (" f =" f,6.4 ¼ 1:21 Â 10 À7 E þ 0:965) and ( f = f,6.4 ¼ 1:51 Â 10 À7 E þ 0:998). Acoustic emission (AE) analysis detected microcracking was increased threefold by shortening the mean fiber length from 6.4 to 0.44 mm. Scanning electron microscopy (SEM) results showed increased fiber/matrix debonding at fiber ends and along fiber lengths in the 0.44 mm samples compared with that reported for 6.4 mm samples. The fiber debonding is thought to impart an internal strain field in the matrix surrounding each fiber resulting in volume expansion sites, hence compressive stress sites which absorb energy from an approaching crack tip front in the nearby vicinity halting the crack's advance. Therefore, more microcracks can be tolerated increasing fracture strain. Moreover, the critical crack length range for thermoset polymers was calculated to be approximately 0:50 < 2a c < 5:0 mm from reported K IC results in the literature, and is greater than the 0.44 mm mean fiber length. The probability of a microcrack propagating above 0.44 mm before it encounters a matrix compressive site, therefore is reduced. Furthermore, increased microcracking in the vicinity of the main crack tip acts to reduce the main crack tip stress concentration. All of these serve to prevent crack propagation resulting in enhancement of fracture strain in the

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

“…However, in the 3-phase filler+fiber+polymer BMC it was previously reported shortening fibers to submillimeter increases tensile fracture strength and its strain ³60 and ³40%, respectively. 2) This study focuses on the related 5 to 25% rise in initial tensile modulus, hence a novel "fiber-spacing" model is constructed. The model obeys the "rule of mixtures" which incorporates modulus of fiber (E f ) and matrix (E m ), fiber volume fraction (V f ), fiber diameter (d), fiber length (l f ) and a factor ( f ) for modulus loss in the fibers by the mixing and injection molding process to be useful in BMC composite design.…”

“…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.…”

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

“…3) However, it was recently reported shortening E-glass bers in an injection molded BMC from commercial 6.4 to sub-millimeter 0.44 mm, below the critical ber length, l c of 1.0 mm, 4,5) yields substantially superior tensile strength and strain increased 58 and 43%, respectively 6) with tensile modulus increased 5-25%. 3) This was a new nding for FRPs: 6,7) up to that time shortening bers to below 1.0 mm was reported to decrease mechanical properties 4,5,[8][9][10] but research was limited to 2-phase FRPs without ller.…”

Effect of Glass Fibers Stacking Sequence on the Mechanical Properties of Glass Fiber/Polyester Composites

“…Some research articles focused on the investigation of the mechanical and impact properties of short glass fiber reinforced composites as reported [15,16]. Recently the authors [17] have studied the notch sensitivity of short and 2D plain-woven glass fibres reinforced with unsaturated polyester and epoxy matrix composites.…”