TY - CONF A1 - Marotzke, Christian A1 - Feldmann, Titus T1 - The influence of local defects and nonlinear matrix behaviour on the failure process of fiber reinforced composites N2 - The premise for the development of improved failure criteria for fiber reinforced composites is the understanding of the failure processes on microscale. On microscale the local behaviour of the matrix polymer is crucial. It significantly differs from that found in macroscopic measurements. The present study is focused on the plastic material behaviour of a standard epoxy resin. Local plastic strains are measured in tensile test by using digital image correlation. A multilinear plastic law is implemented by the experimental data. The stress field arising in an idealised representative volume element of a unidirectional ply is analysed by finite element calculations. The change of the stress and strain field due to plastic deformation according to the multilinear plastic law is shown. The change leads to a shift of the critical locations where failure is likely to initiate. In addition, the failure type changes from stress based to strain based failure. The dominant role of the shear strains is shown. T2 - ECCM17 CY - Munich, Germany DA - 27.06.2016 KW - failure mechanisms KW - plasticity KW - micromechanics KW - interfacial stresses KW - local deformation PY - 2016 SN - ISBN 978-3-00-053387-7 SP - 1 EP - 8 CY - München AN - OPUS4-37863 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian A1 - Feldmann, Titus T1 - Failure of fiber reinforced composites under multiaxial stresses on microscale N2 - The failure of composites is initiated by imperfections on microscale. The interface between fiber and matrix is a key parameter concerning failure initiation. In order to get an improved understanding of local failure processes a fracture mechanical analysis of interfacial failure in a composite ply under transverse stresses is performed. The mixed mode energy release rate is calculated. In addition the failure of interfaces under cyclic loading is studied on a single fiber model. The quasistatic debonding process is compared with the interfacial failure under fatigue loading. It is shown that the tan delta can be used as an indicator for the damage propagation. T2 - ICMFF11 CY - Sevilla, Spain DA - 01.06.2016 KW - failure mechanics KW - failure mechanisms KW - multiaxial loading KW - micromechanics PY - 2016 SP - 1 EP - 8 AN - OPUS4-37864 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian A1 - Feldmann, Titus T1 - Nonlinear time dependent behaviour of epoxy resins N2 - The nonlinear behaviour of epoxy resins is studied on standard tensile tests. A strain field measurement system is applied (Aramis) in order to monitor local strains. The residual strain is measured by recovering the specimens for up to 68 hours after unloading. The time span the specimen is exposed to load has a large influence on the creeping process and the residual strain after recovering. This is studied by comparison of instantaneous unloading with keeping the specimen under permanent load for thirty minutes. It is shown that moderate differences in the initial strain can lead to large differences in the creep behaviour as well as in the residual strain. T2 - 37th Risø International Symposium on Materials Science CY - Risø, DK DA - 05.09.2016 KW - composites KW - epoxy resin KW - viscoelasticity KW - plasticity PY - 2016 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-378552 DO - https://doi.org/10.1088/1757-899X/139/1/012035 SN - 1757-8981 VL - 139 SP - Article 012035, 1 EP - 8 PB - IOP Publishing CY - London AN - OPUS4-37855 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -