Development and preliminary performance evaluation of discontinuous fibre reinforced thermoplastic leaf spring

Abstract

Leaf spring plays a significant role in the riding comfort of an automobile. Thermoplastic composite materials are replacing many metallic parts in an automobile system. The main objective of the present work is to identify the scope of thermoplastic composite material for leaf spring application. Emphasis is given to understand the effect of reinforced fibre length on the leaf spring performance. In all, 20 per cent discontinuous long and short glass fibre reinforced polypropylene (PP) materials were considered for the development. Prior to the development and evaluation of leaf springs, the influence of reinforced fibre length over leaf spring material behaviour has been investigated. With the increase in reinforced fibre length, crystallinity of the base matrix structure, thermal characteristics, and mechanical behaviour under static and dynamic loading conditions were found to be improved. Mono, discontinuous fibre reinforced thermoplastic leaf spring of varying width is designed and injection molded. A servo-hydraulic fatigue testing facility coupled with linear guide ways is utilized to evaluate the preliminary leaf spring performance parameters, namely load deflection, strain rate sensitivity, hysteresis, and damping behaviour. Preliminary test results on composite leaf spring confirmed that long glass fibre reinforced PP leaf spring is able to carry three times the load for a design deflection than short glass fibre reinforced PP leaf spring. This improved spring rate behaviour results in significant improvement of the energy-absorbing capability. The influence of strain rate over the load deflection behaviour of long fibre reinforced leaf spring is found to be less than that of short fibre reinforced leaf spring. However, the damping behaviour of short glass fibre reinforced leaf spring is found to be superior to that of long glass fibre reinforced leaf springs.

Fatigue performance of discontinuous fibre-reinforced thermoplastic leaf spring

“…X-ray diffraction investigation of test leaf spring material reveals that the crystallite sizes of UFPP, SFPP, and LFPP are 100.33, 118.615, and 146.784 Å, respectively. Material crystallinity is found to be influenced by reinforcement as well as length of reinforcement; more details were reported elsewhere [10]. Details of injection moulding conditions of the leaf spring are presented in Table 1.…”

“…1. Details of injection-moulded leaf spring and fixture for the leaf spring testing are reported elsewhere [10]. Test leaf springs are loaded up to 12 mm deflection (Camber) and released back as per the SAE standard J 1528 [17].…”

“…The desire to increase the volume of production has initiated this study of thermoplastic composites for leaf spring applications. Development and static performance evaluation of short glass fibre-reinforced polypropylene (SFPP) and long glass fibre-reinforced polypropylene (LFPP) leaf springs are reported elsewhere [10]. Since leaf springs are subjected to fatigue loading in the service, this current work attempts to understand the performance of thermoplastic composite leaf spring under the fatigue condition.…”

Long discontinuous carbon fibre/polypropylene composites for high volume structural applications

“…Cracks in randomly orientated fibre composites are impeded by the discontinuities, such as fibre cross-overs [29], and either propagate through the matrix or along the interface, depending on the interfacial strength [30]. When the interface is weak, these interfacial cracks propagate along the length of the fibre and lead to fibre pull-out [31]. This was demonstrated by the CF.PP samples, as the tows separated during fracture and the ends were flexible and free of matrix.…”

“…Despite fibre breakage and pull-out accounting for a large proportion of the fracture energy, there must be sufficient matrix to transfer stresses efficiently. It is understood that fibre fracture leads to stress intensification [43] and cracks therefore propagate through the matrix for high interface strength systems, as opposed to along the interface [31]. This is exacerbated at higher volume fractions as the inter-fibre spacing is reduced and may lead to brittle failure characteristics, therefore the plateau in impact strength is caused by a change in failure mode of the matrix material.…”