Stress-strain synchronization for high strain rate tests on brittle composites

Abstract

Nowadays, many researchers develop rate-dependent composite material models for application in dynamic simulations. Ideally, full stress-strain curves at a wide range of strain rates are available for identification of the different parameters of these models. Dynamic tensile tests are needed to produce the experimental input data. However, especially for brittle materials, the data acquisition during these tests becomes critical. The effect of synchronization on the test results is investigated by conducting a series of dynamic tensile tests on three different brittle continuous-fibre composite laminates. It is demonstrated that synchronization errors of the order of 1 microsecond already have a significant effect on the test outcome at high rates. With the aid of a finite-element model, the limiting factors on the maximum attainable strain rate are quantified.

On the Identification of Orthotropic Elastic Stiffness Using 3D Guided Wavefield Data

“…This deviation is partly due to the difference between the samples and materials used in our study and in other cases in the literature, and partly to the homogenization calculation of the parameters which only provides a rough estimate for a layered medium when starting from the unidirectional ply parameters. This is conform with recent literature reports [11,37] where the inverted stiffness parameters (C 12 , C 13 and C 23 ) were found to be almost 2.5 times higher than homogenized stiffness values, and also in line with the information coming from different manufacturers stating that the deviation in material properties (which were used as the basis for the homogenization calculation) might amount up to 10%. In order to validate the accuracy of the inversion results, the SAFE-based calculated wavenumber-frequency pairs corresponding to the optimized stiffness parameters of full-field motion inversion (red dots) are plotted in Figure 8, together with the MPDM-based extracted values from the experimental recordings (black open circles) and the experimentally obtained dispersion curves obtained through the 2D FFT of the star-like gridded laser Doppler vibrometer data, transforming (x, t; θ) data into (k, f ; θ).…”

Dynamic Tensile Testing of Brittle Composites Using a Hydraulic Pulse Machine: Stress-Strain Synchronization and Strain Rate Limits

“…The only option is to analyse the delay of each component in the chain of data acquisition to allow for an automatic synchronization [6]. Both the start or the end of the test are namely not discrete enough at high speed to be used to accurately align the data streams.…”

Optimization of a Tapered Specimen Geometry for Short-Term Dynamic Tensile Testing of Continuous Fiber Reinforced Thermoplastics

“…To estimate the strain rate of rectangular specimens even before testing, the nominal strain rate . ε nom is defined as quotient of the target test speed v 0 and the free clamping length of the test specimen l 0 , according to Equation (2) [7,8].…”

“…Quasi-static as well as high strain rate testing (up to 6000 s −1 in Split Hopkinson Bar testing) are deeply investigated research areas (e.g., [9][10][11][12]). A gap appears in short-term dynamic tensile tests on cFRTP materials in a medium strain rate spectrum (1 to 100 s −1 ) for which only isolated preliminary work exists [6,8,13]. This strain rate area is addressed in this work, forming the basis of a cFRTP test method necessary for material applications, e.g., in the automotive sector [14].…”

“…The actual focus in the literature is on composites with thermoset matrices. Table 1 summarizes different specimens with a dogbone (Fitoussi et al [22], Todo et al [23]), tapered (Spronk et al [8], Chen et al [24], De Baere et al [25], Gilat et al [26]), and rectangular shape (Hufner/Hill [27]). In comparison, not only the specimens' shapes but also the dimensions vary widely.…”