Comprehensive Evaluation for Joint Strength of Ultrasonic-Welded CFRTP involving Interface and Resin Strengths
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Minori ISOZAKI (JAPAN), Maruri TAKAMURA (JAPAN), Shinichi TAKEDA , Jun KOYANAGI (JAPAN)Abstract :
In this study, we propose a comprehensive method to evaluate the joint strength of ultrasonic-welded carbon-fiber-reinforced-thermosetting-plastic (CFRTP). Ultrasonic welding is one of the promising joining methods for CFRTP that are expected to apply to bonding large parts such as aircraft components, but this welding has not been generally applied because the quantitative evaluation method for assessing joint strength has not been established yet.
First, we point out the issues with the current evaluation methods. Presently, joint strength is evaluated based on the experimental results of a single-lap-shear test. However, this method shows "Apparent strength" which, in practice, does not take into account the non-uniform stress distribution in the joint or failure under combined shear and normal stresses. Therefore, we propose a new method to evaluate the "True strength" of a joint, considering the stress state and the initiation of failure.
There are two possible initiations of failure for joint: (a) delamination of the joint interface and (b) resin failure within the joint resin. In our approach, to comprehensively assess the joint strength, including the differences in the initiation of failure, we first clarify the (a) Interface strength and (b) Resin strength. The derivation methods are as follows:
(a) Interface Strength: For ultrasonic-welded CFRTP, we conducted strength tests in two directions: "Shear test by Compression" and "Flatwise Tensile test". Based on the results, stress analysis using Abaqus is performed to derive the accurate stress state at the joint interface during failure. Then a failure envelope based on a parabolic criterion was created from the analysis results[1].
(b) Resin Strength: We adopt Christensen's fracture criterion as the failure criterion for resin[2]. From this theory and material properties obtained from previous research, we create a failure envelope on a two-dimensional plane representing resin strength.
We integrate the failure envelopes created for interface strength and resin strength on the same plane, creating an inclusive 'Comprehensive Failure Envelope' that considers the initiation of both interface and resin failures. The advantage of proposed failure envelope today lies in the ability to consider the following three elements on a single envelope: (1) Failure initiation, (2) Failure under combined stress state, (3) Stress distribution at the joint.
By using the strength evaluation methods we propose, it becomes possible to evaluate the true strength of adhesive or welded joints, including ultrasonic welding. This allows the way for the realization of welding and adhesive joints in large structures. In this study, we also evaluate and discuss the strength of ultrasonic-welded CFRTP under different welding conditions such as welding time, pressure, and resin type by using this method.
First, we point out the issues with the current evaluation methods. Presently, joint strength is evaluated based on the experimental results of a single-lap-shear test. However, this method shows "Apparent strength" which, in practice, does not take into account the non-uniform stress distribution in the joint or failure under combined shear and normal stresses. Therefore, we propose a new method to evaluate the "True strength" of a joint, considering the stress state and the initiation of failure.
There are two possible initiations of failure for joint: (a) delamination of the joint interface and (b) resin failure within the joint resin. In our approach, to comprehensively assess the joint strength, including the differences in the initiation of failure, we first clarify the (a) Interface strength and (b) Resin strength. The derivation methods are as follows:
(a) Interface Strength: For ultrasonic-welded CFRTP, we conducted strength tests in two directions: "Shear test by Compression" and "Flatwise Tensile test". Based on the results, stress analysis using Abaqus is performed to derive the accurate stress state at the joint interface during failure. Then a failure envelope based on a parabolic criterion was created from the analysis results[1].
(b) Resin Strength: We adopt Christensen's fracture criterion as the failure criterion for resin[2]. From this theory and material properties obtained from previous research, we create a failure envelope on a two-dimensional plane representing resin strength.
We integrate the failure envelopes created for interface strength and resin strength on the same plane, creating an inclusive 'Comprehensive Failure Envelope' that considers the initiation of both interface and resin failures. The advantage of proposed failure envelope today lies in the ability to consider the following three elements on a single envelope: (1) Failure initiation, (2) Failure under combined stress state, (3) Stress distribution at the joint.
By using the strength evaluation methods we propose, it becomes possible to evaluate the true strength of adhesive or welded joints, including ultrasonic welding. This allows the way for the realization of welding and adhesive joints in large structures. In this study, we also evaluate and discuss the strength of ultrasonic-welded CFRTP under different welding conditions such as welding time, pressure, and resin type by using this method.