Elsevier

Materials Letters

Volume 264, 1 April 2020, 127362
Materials Letters

Fatigue response of ultrasonically welded carbon/Elium® thermoplastic composites

https://doi.org/10.1016/j.matlet.2020.127362Get rights and content

Highlights

  • fatigue strength of ultrasonically welded composite joints with Elium® resin.

  • 10–12% higher fatigue life as compared to the adhesively bonded joints.

  • Optimised bonding time for welded samples is 1 s and adhesive bonding is 10 min.

  • Fibre impingement and shear cusps phenomenon led to strong interfacial adhesion.

Abstract

Current research aims at investigating the fatigue strength of ultrasonically welded composite joints with novel liquid acrylic thermoplastic Elium®. Fatigue response of the welded joints with integrated Energy Director (ED) and flat Elium® film was investigated and the baseline comparison was carried out with control adhesives. The results showed 10–12% higher fatigue life at 105 and 106 fatigue cycle as compared to the adhesively bonded joints. Fractographic investigation of fractured welded joints showed features such as fibre impingement and shear cusps formation which contributed to strong interfacial adhesion.

Introduction

Ultrasonic welding is an ultrafast process of joining thermoplastic composites and works on the principle of converting the low and high amplitude oscillations (vibrations) to heat at the interface of the joining surfaces [1], [2], [3], [4]. Ultrasonic welding possesses distinct advantages over other fusion bonding methodologies viz. the weld strength can reach the neat polymer strength, can be bonded in few seconds and is independent of using an extra material at the interface as required in resistance and other welding. So, ultrasonic welding is widely getting attraction in many industrial applications such as joining of thermoplastic composite parts in aerospace and automotive industries, wire binding in electronics and in the packaging industry for sealing purposes.

Recently a novel acrylic thermoplastic resin, Elium® has been developed by Arkema which is a first of its kind to cure at room-temperature. Already, significant research is reported in the literature investigating the impact [5], [6], fracture toughness [7], vibration [8], flexure [9], [10], tensile [11] and other mechanical attributes of this novel resin system with different fibre reinforcements. Murray et.al. [12] has carried out a research on the fusion bonding of the Elium® composite using resistance welding with different heating elements and induction welding techniques to investigate to weld attributes of the Glass fibre Elium® composites for wind turbine blade applications. At 107 cycles (defined stress for no failure), the fatigue limit for a fusion-welded sample was found to be 5 MPa as compared to 3 MPa in the case of the adhesively bonded sample.

Current research aims at investigating the fatigue response of ultrasonically welded novel carbon Elium® composite parts which could pave an excellent way of joining these composites in an industrial landscape.

Section snippets

Materials and methods

For thermoplastic composite manufacturing, FOE sized 12 K 2x2 twill weave carbon fibers (FAW 380 gsm) from CHOMARAT were used as the reinforcement and Elium® 150 resin, provided by Arkema, France was used as the matrix material. Elium® resin undergoes radical polymerization with benzoyl peroxide initiator at a mixing ratio of resin to hardener 100:3 [13]. For adhesively bonded joint, SAF 30 5 adhesive from Bostik was used.

For manufacturing of composite laminate, Resin Transfer Moulding (RTM)

Fatigue testing of bonded joints

After the optimization study with different welding parameters of weld time and weld pressure the ELC_IED configuration was welded at 1 s weld time, 4 bar weld pressure and at an amplitude of 49 μm. The static Lap shear strength (LSS) obtained for ELC_IED was found to be 18.86 MPa ±0.14. Whereas ELC_FED was welded at 5.5 s weld time, 3 bar weld pressure and amplitude of 33 μm and the obtained LSS value was 14.04 MPa ±0.01. The static LSS obtained for adhesively bonded joint was 14.2 MPa. Fig. 2

Conclusions

Fatigue strength of ultrasonically welded Elium® composites is investigated with integrated ED and flat Elium® film. The fatigue strength of welded joint with integrated ED was consistently higher (7%–12%) at the all applied stresses compared to the baseline adhesively bonded samples. The increase is attributed to the fibre impingement and shear cusps formation which contributed to strong interfacial adhesion. Whereas, the strength was slightly lower at higher applied stress values for the

CRediT authorship contribution statement

Somen K Bhudolia: Conceptualization, Methodology, Investigation, Writing - review & editing. Goram Gohel: Conceptualization, Methodology, Investigation. Leong Kah Fai: Supervision, Funding acquisition. Robert J. Barsotti: Writing - review & editing, Project administration.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

Authors would like to acknowledge the financial support from the Institute for Sports Research, Nanyang Technological University, Singapore and ARKEMA, France under the work carried out on RCA-18/46.

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