The first ever functional specimen holder is numerically simulated to understand the static and dynamic system response to a physically complex interface damage evolution. To solve the above challenges of measurement and reveal the true behaviour of filament-polymer interfaces, an especial compound basic parallelogram mechanism (CBPM) with an integrated FBG sensor is studied here.
If tests are carried out in an outdoor environment or an environmentally controlled chamber with air circulation, the air fluctuation and related temperature variations in each FBG need to be balanced by a separate FBG for this function. The applied connector element must be kept well aligned and intact. At least one connection between the specimen of measurements and the data acquisition is always needed. Therefore, all connections should be minimized practical connections of optical fibres require occasional cleaning and care when re-connected. The optical path (fibre) to the sensor (FBG) must be clean and perfect for error-less and strong laser signal. However, they are not as robust as strain gauges, for example. FBGs can provide long-term, stable measurements with essentially zero drift and fatigue durability. The flexural hinges provide high motion resolution, negligible cross-coupling errors and fast response and make it a superior candidate for a system with micro-scale droplet-filament specimens and FBG sensor technology for measurements. The strain sensitivity enhancement using compliant flexural hinges have demonstrated a high precision and accuracy in strain measurements 20. (3) The inertia and dissipation in the measurement system must be minimized for the sensor to follow the dynamics of the specimen during testing. (2) Any compliant mechanism 19 that can transmit the specimen’s deformation to the strain sensor, must possess a high resilience. Integrated optical sensors are potential to solve the interfacial measurements yet several challenging aspects are to be considered: (1) For a laser-excited Fibre Bragg grating sensor (FBG), the location of the sensing point must be exactly in line with the specimen. Through the years, these drawbacks have prevented researchers from producing reliable interface data and highly optimized composite applications. The MB test is also prone to various sources of errors, such as load measurement, device optics and resin curing, which can lead to high scattering in test results 18. Due to the small size, a displacement sensor for a micrometer-length scale interface cannot be fixed to the specimen but to the test machine structure-being prone to various lags and compliance 16, 17. Naturally, the control signal is independent of the filament and matrix and, therefore, cannot sense the specimen’s behaviour. To date, the device outputs include only force recordings and specimen or blade displacement from a sensor or the control signal (i.e., blade or grip area of the filament depending on the test method) 15. The developed strain-sensing CBPM-FBG holder shows excellent sensitivity during the MB tests for both synthetic and natural filaments, even at a low filament diameters as low as \(7\,\upmu \hbox \), and the measured reaction forces ( F) vary from 0–1 N 13, 14. Quasi-static and dynamic analysis of the MB testing is carried out by using the FE method to interpret the response of the compliant structure. Qualification experiments are carried out to confirm the functional performance: MB testing of synthetic (carbon and glass) and natural (flax) single filaments are successfully performed. The stiffness of the compliant structure is estimated by using mathematical and finite element (FE) models. In this paper, a monolithic compliant based structure with an integrated Fiber Bragg Grating (FBG) sensor is developed and analysed. As a fundamental basis, the momentary reaction force and respective local strain at the location of a non-ambiguous gradient are needed for a mechanical analysis.
The traditional MB test systems provide unitary data output (i.e., converted force) which is enigmatic in resolving the fracture parameters of multi-mode interface cracks. The characterization of adhesion between single filament and picoliter-scale polymer matrix usually relies on the experiments using so-called microbond (MB) testing. Especially the applications of fibrous composites in miniature products, dental and other medical applications require accurate data of microscale mechanics.