95 © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 L. Lamberson et al. (eds.), Dynamic Behavior of Materials, Volume 1, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-59947-8_17 Chapter 17 High Strain Rate Characterization and Impact Analysis of Fiber Reinforced Composites Karthik Ram Ramakrishnan, Gustavo Quino, Justus Hoffmann, and Nik Petrinic Abstract Fiber reinforced polymer (FRP) composite materials have been used in aerospace applications such as engine blades, brackets, interiors, nacelles, propellers/rotors, and single aisle wings. It is well recognized that composites are sensi- tive to damage caused by impact during their service life. A complete constitutive model of composite material that can predict the mechanical performance and the development of damage leading to failure is still an on-going research endeavor. An essential step in the development of constitutive model is dynamic mechanical characterization including tensile, shear, and compressive loading using various testing techniques such as servo-hydraulic system, high rate servo-hydraulic machine, and Split Hopkinson Pressure Bar (SHPB) to properly satisfy critical design requirements. In this chapter, a comprehensive approach combining micromechanical modeling, dynamic mechanical characterization, and macroscale Finite Element modeling is presented to study the high-velocity impact response of carbon fber reinforced composites manufactured from UD tapes. Keywords Composites · High strain rate · Ballistic impact · DIC 17.1 Introduction Fiber reinforced polymer (FRP) composite materials have been used in aerospace applications such as engine blades, brack- ets, interiors, nacelles, propellers/rotors, and single aisle wings. It is well recognized that composites are sensitive to damage caused by impact during their service life. The behavior of composite structures including the effects of damage is very complex and is dependent on a range of parameters including the geometry, material, lay-up, loading conditions, load his- tory, and failure modes. It is important to understand the dynamic behavior of composites and to develop numerical models which can capture the dynamic response accurately as these materials are often used in applications where they are fre- quently subjected to dynamic loads. Several researchers have studied the strain-dependent properties of composites and their constituent materials [1]. It is generally well-accepted that the epoxy resin used as matrix material in the composites exhibits rate sensitivity. Signifcant increase in failure strength and apparent elastic modulus has been observed with increasing strain rate, while the strain to failure decreases at higher rates [2]. It is also widely reported that there are two regimes, frst up to 100 s -1 where the rate sensitivity is low and higher rates where there is a marked increase. Ductile to brittle transition in higher rates have also been reported for epoxy matrix [3]. High rate testing of carbon fbers have shown that the tensile modu- lus and strength in the longitudinal direction are independent of the strain rate [4]. It was also reported that transverse and shear properties increase with strain rate, with shear strength displaying stronger strain-rate dependence. Gilat et al. [5] reported that sensitivity to strain rate of CFRP composite is driven by the resin behavior. Results from testing uniaxial T800/ F3900 composite plate shows no strain rate effect in compression in the 0° direction, while signifcant strain rate effects in compression and tension in the 90° direction, and in shear were reported by Gilat and Seidt [6]. However, recently Zhang et al. [7] reported that even though strain rate dependency is not obvious under 20 s -1 for unidirectional CFRP, the tensile strength, Young’s modulus, and failure strain increase remarkably with the increase of strain rate over 20 s -1 . The possible cause of contradictory results include that there are no standard test methods and specimen geometries used by the different researchers. For instance, some tests used drop tower or hydraulic systems instead of SHTB. Clamping and data reduction K. R. Ramakrishnan (*) · G. Quino · J. Hoffmann · N. Petrinic Department of Engineering Science, University of Oxford, Oxford, UK e-mail: karthik.ramakrishnan@eng.ox.ac.uk; gustavo.quinoquispe@eng.ox.ac.uk; justus.hoffmann@eng.ox.ac.uk; nik.petrinic@eng.ox.ac.uk