Marco L Longana

Approaches to Synchronise Conventional Measurements with Optical Techniques at High Strain Rates

Polymer composites are increasingly being used in high-end and military applications, mainly due to their excellent tailorability to specific loading scenarios and strength/stiffness to weight ratios. The overall purpose of the research project is to develop an enhanced understanding of the behaviour of fibre reinforced polymer composites when subjected to high velocity loading. This is particularly important in military applications, where composite structures are at a high risk of receiving high strain rate loading, such as those resulting from collisions or blasts. The work described here considers an approach that allows the collection of full-field temperature and strain data to investigate the complex viscoelastic behaviour of composite material at high strain rates. To develop such a data-rich approach digital image correlation (DIC) is used to collect the displacement data and infra-red thermography (IRT) is used to collect temperature data. The use of optical techniques at the sampling rates necessary to capture the behaviour of composites subjected to high loading rates is novel and requires using imaging systems at the far extent of their design specification. One of the major advantages of optical techniques is that they are non-contact; however this also forms one of the challenges to their application to high speed testing. The separate camera systems and the test machine/loading system must be synchronised to ensure that the correct strain/temperature measurement is correlated with the correct temporal value of the loading regime. The loading rate exacerbates the situation where even at high sampling rates the data is discrete and therefore it is difficult to match values. The work described in the paper concentrates on investigating the possibility of the high speed DIC and synchronisation. The limitations of bringing together the techniques are discussed in detail, and a discussion of the relative merits of each synchronisation approach is included, which takes into consideration ease of use, accuracy, repeatability etc.

Development and application of a quality control and property assurance methodology for reclaimed carbon fibers based on the HiPerDiF (High Performance Discontinuous Fibre) method and interlaminated hybrid specimens

Abstract To promote the usage of recycled composite material, it is of paramount importance to develop quality control and property assurance methodologies compatible with the format of reclaimed fibers. In this paper, the concept of using interlaminated hybrid specimens, whose tensile response has been tailored with the aid of the Damage mode maps, is exploited to unambiguously identify the reclaimed fibers failure strain. The interlaminated hybrid specimens are manufacturing by sandwiching a layer of aligned discontinuous reclaimed carbon fibers produced with the HiPerDiF (High Performance Discontinuous Fibre) method between continuous glass fibers. The reliability of the obtained results is compared with results obtained with single fiber tensile tests. The developed methodology is then applied to the investigation of the strength retention of carbon fibers reclaimed through a solvolysis process and to the effects of the fiber length on the HiPerDiF alignment process. Graphical Abstract