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 reinforcement with thermoplastic glass-fibre tapes offers a way to reduce the amount of material used in injection-moulded components while maintaining a specified stiffness. Earlier simulations and practical studies under conditions close to series production showed that one unit by weight of unidirectional glass-fibre tape could replace 13 units by weight of injection-moulding compound, without tape-induced component distortion or a loss of stiffness.
Further use of the technology depends in particular on understanding the bond between the tape and the injection-moulding compound. Differences in stiffness and thermal expansion can generate residual stresses at the interface during injection moulding. These stresses may cause premature interfacial failure and compromise the component’s structural integrity. Reliable measurement of bond strength therefore needs to take account of residual stresses in the test specimen and the temperature history during processing. This calls for test methods capable of measuring temperature and strain histories in the bond region.
© 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
