Innovative testing methods for the characterisation of the bonding strength of UD tapes in injection moulded components
Thermoplastic glass fiber tapes offer enormous lightweight construction potential for injection-moulded components. In order to overcome material and process-related challenges such as residual stresses and interface failure, innovative tape inserts with integrated fiber optic sensors enable the precise measurement of temperature and strain histories. This enables a well-founded characterisation of the bond strength under real conditions.
Initial situation / problem:
Local reinforcements in injection-moulded components with thermoplastic glass fiber tapes open up significant lightweight construction potential, which meets the economically and increasingly also ecologically driven imperative for lightweight structural design in large-scale production applications. This opens up new, economically viable and environmentally friendly design approaches for injection moulded components. Previous simulative and practical studies have already shown in large-scale production that the use of cost-effective unidirectional glass fiber tapes can save injection moulding compound in a ratio of one weight unit of tape to 13 weight units of injection moulding compound. This is achieved without tape-induced component distortion and with consistent component rigidity. However, material differences in stiffness and thermal expansion between the injection moulding compound and the glass fiber tape lead to considerable residual stresses in the bonding area, particularly during the injection moulding process. This can result in premature failure along the interface and the associated loss of structural integrity of the component. Consequently, the characterisation, modelling and testing of the bond strength between tape and injection moulding compound as a function of the material and process variables is a necessary intermediate step for the further establishment of tape technology for injection moulded components. However, the test specimens required for this are themselves subject to a tape-induced residual stress state that cannot yet be characterised, making it impossible to measure the true bond strengths without further ado. In addition, in-situ measurement of the temperature history in the bonding area between the tape and the injection moulding compound is not possible with current measuring methods. Consequently, there is a need for new test methods to characterise the bond strength, taking into account the temperature history.
© IKVObjective:
In order to develop test methods for characterizing the bond strength, taking into account the temperature history, new types of tape inserts with integrated fiber-optic temperature and strain sensors are being investigated. This should enable the measurement of the temperature history in the injection moulding process and a measurement of the local strain in the test specimen after injection moulding.
Solution and results:
The insertion of sensor fibers, which are mechanically coupled to the laminate of the insert, makes it possible to measure the local elongation state. The mechanical decoupling of the sensor fibers from the laminate, for example through the use of capillary tubes, in turn allows local temperature measurement. This allows conclusions to be drawn about the predicted bond strength and an adjusted measurement of the bond strength.
Project data and funding
The work presented was funded by the German Research Foundation (DFG) and the National Science Foundation (NSF) as part of the research project “NSF-DFG: Multiscale Data-Physics Models for the Critical Role of Interfaces in Overmolded Thermoplastic Parts”. Our sincere thanks go to her.
Project duration: 3/2024 – 2/2027
Project partners
