The Effects of Weld Geometry and Glass-Fiber Orientation on the Mechanical Performance of Joints – Part I: Weld Design Issues

Abstract

The mechanical performance of injection molded glass-fiber reinforced [thermo]-plastic components is anisotropic and depends on the fiber orientation and distribution. The purpose of this comprehensive analysis is to show the relationship between short-fiber orientation at the prewelded bead and wall areas, and the mechanical performance of welded butt-joints that have various geometry and thickness, namely ‘‘straight’’ and ‘‘T-type’’ welds. Findings on the mechanical performance of these two different types of butt-joints by the design and geometry butt-joints will help designers and technologists with material selection, welding processing, and design optimization. In a subsequent paper (Part II)1, we related these findings to the kinetics of glass-fiber reorientation and micro-structural changes and how they influence part and weld design.

Fatigue properties of vibration-welded nylon 6 and nylon 66 reinforced with glass fibres

“…The non-welded specimens of reinforced nylon 66 had statistically higher tensile strength than the welded specimens. This result was expected as the glass fibres at the weld are generally oriented in the weld plane and thus offer little reinforcement when stress is applied normal to this interface [5,14,16]. Among welded reinforced nylon 66 specimens, low weld pressure yields superior tensile weld strengths than high weld pressure.…”

“…The fibre orientation is influenced by the flow of the material during injection moulding [5,11,13,14]. It is accepted that the preferential fibre orientation in thin edge-gated plaques is parallel to the melt flow direction during cavity filling as shown in Fig.…”

Microstructure-mechanical properties relationships in vibration welded glass-fiber-reinforced polyamide 66: A high-resolution X-ray microtomography study

“…To evaluate the efficiency of the welding operation, the weld ratio is presented in Table 1. Results confirm that, contrary to pristine polymers where weld ratio close to 1 can rather easily be obtained, welding of fiber reinforced polymers is much less efficient as all weld ratio vary between 0.5 and 0.65 [12]. Table 2 displays the molecular weights of non-welded and welded PA66-GF30, for all conditions.…”

“…These studies also reveal that, as predicted in equation 1, a lower applied pressure actually results in a thicker heat-affected zone for unreinforced polypropylene (PP) [10,11] and polyamide 6 (PA6) [8], and leads to assemblies with improved mechanical properties, in particular higher tensile stress at break. Indeed, with well-chosen processing conditions, the weld ratio, defined as the tensile stress at break of the welded material divided by the tensile stress at break of the bulk one, can reach 0.97 for such pristine polymers [12].…”

“…However, this weld ratio decreases significantly with the addition of short glass fibers in the polymer matrix, down to ~0.5 for 30% glass fiber reinforced polymers [12]. The mechanisms explaining this drastic loss of mechanical properties for short-fiber composites during welding are not fully understood [13] and can have catastrophic consequences, for example when a backfire occurs in the air intake manifold [3].…”