(72f) The Dynamic Mechanical Performance of Glass Fiber Reinforced Thermoplastic Composites

Thermoplastic composites are being widely used as structural, semi-structural and functional parts to meet the light weighting trend of materials. In the past decades, the emphasis on research on strength and rigidity had resulted in many high mechanical performance composites being manufactured and used in various areas, such as automobile, aerospace, construction and civil engineering. Since many composite parts are subjected to random loading, especially impact loading in service, the response and failure behaviors under these situations are increasing concern.

In this paper, the glass fiber reinforced thermoplastic composites were prepared by melt impregnation method using the double steel belt press. The strength and stiffness, the dynamic mechanical properties including notched impacting, alternating stress and multi-axis impacting of thermoplastic composites were investigated; the effects of the compatibilizer content, long glass fiber mat needle fixation structure, fiber reinforcement type, and the multi-axis force loading rate on composites performance were discussed.

The effect of compatibilizer on mechanical performance of composites was studied. The results show that strength and rigidity of composites are improved with modified matrix, but the toughness is significantly deteriorated with higher compatibilizer loading. However, in the case of using 1% compatibilizer modified PP matrix, the composites can gain improved notched impact strength of 124.66 kJ/m2 with strength and rigidity increasing, and at the same time have maximum load of 6320 N and piercing energy value of 54.32 J by the synergistic effect between glass fiber and resin in multi-axis impact. DMA frequency spectrum analysis shows that the storage and loss modulus of composites are the highest at 5% of compatibilizer in the range of 0.5 to 100 Hz, on the other hand damping property of composites at 1% of compatibilizer increases sharply at 150 Hz, in accordance with good toughness.

The influence of long glass fiber mat needle fixation on composite properties was investigated. It is concluded that the strength and rigidity of thermoplastic composites are optimal at 30 st/cm2 and DMA storage modulus at 15 st/cm2 in the range of needle density of 0~90 st/cm2; while needling density has little effect on loss index in DMA. For the multi-axial impact, piercing energy of composites increases first and then decreases with the increasing of needling density, reaching the maximum value of 26.07 J at 30 st/cm2, which is 21.0% more than that of the non-needle sample.

The multi-axis impact piercing energy of composites with different fiber reinforcement structure follows the order of continuous mat> chopped mat> mixed fiber> LFT> long glass fiber mat. The continuous mat reinforced composite has the maximum piercing energy of 36.69 J, which is 40.7% higher than the minimum value. The failure morphology shows that the broken pieces of continuous and chopped mat reinforced composites are closely connected with the bulk body, while the long glass fiber mat and mixed fiber mat-composites are easier to produce larger debris, and the case of LFT falls in between them.

Under the impact loading rate of 2.895 m/s and 3.607 m/s in the multi-axis impact test, the continuous mat and chopped mat-composites have the similar mode of stress response and failure morphology with more brittleness, lower piercing energy, smaller damage area at higher speed. However, long glass fiber mat and mixed fiber mat-composites have another pattern, where piercing energy and damage area increase at higher speed.