TY - CONF A1 - Marotzke, Christian A1 - Feldmann, Titus ED - Thomson, Ole T1 - Characterisation of failure processes of composite plies under transverse loading T2 - Proceedings of the ICCM20 N2 - For the design of laminates the knowledge of the failure behaviour of plies under multiaxial stresses is a necessary precondition. The strength of plies under multiaxial stresses commonly is determined by standard off-axis tests using fixed clamps. By varying the off axis angle the ratio of shear to normal stresses can be prescribed. However, by preventing the rotation a complex stress field develops which strongly varies with the off axis angle as well. While these effects are not crucial when determining the elastic material parameters since the stress state in the center of the specimen is not far from the ideal uniaxial stress state they have a great influence on the failure behaviour. T2 - ICCM20 CY - Copenhagen, Danmark DA - 19. 07. 2015 KW - debonding KW - composites KW - failure process KW - fracture mechanics KW - energy release rate PY - 2015 UR - www.iccm-central.org/Proceedings/ICCM20proceedings/ VL - 2015 SP - Paper No. 3314-4 page 01 EP - Paper No. 3314-4 page 09 AN - OPUS4-36414 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian A1 - Feldmann, Titus T1 - Influence of loading rate and loading time on mechanical behaviour of epoxy resins N2 - Epoxy resins are frequently used for advanced fiber reinforced composites applications. Even though the fibers are dominating strength and stiffness of the composites, specifically when loaded in fiber direction, the failure usually initiates in the matrix near or directly at the interface. Especially in plies loaded transverse to the fiber direction, the mechanical behaviour is highly influenced by the mechanical properties of the epoxy matrix. Accordingly the mechanical properties of the matrix are of great importance. T2 - 10th International conference on the mechanics of time dependent materials (MTDM) CY - Paris, France DA - 17. 06. 2016 KW - Viscoelasticity KW - Epoxy resin KW - Loading rate KW - Relaxation KW - Residual strain PY - 2016 AN - OPUS4-36407 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 – role of the matrix behaviour and the interface strength N2 - Failure of fiber reinforced composites initiates at microdefects in the matrix or at the interface. The interface strength is calculated from the stress field directly before crack initiation by nonlinear finite element simulations. Large deformations and plastic material behaviour are taken into account. Microscopical inspections of the fibers after failure show only small regions with adhering matrix material. This indicates that the interface strength is below the matrix strength. T2 - 2nd International Conference on Mechanics of Composites CY - Porto, Portugal DA - 12.07.2016 KW - composites KW - fracture mechanics KW - nonlinear material behaviour PY - 2016 AN - OPUS4-36905 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - 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 aim of the paper is to analyse the failure process taking place on microscale in fiber reinforced composites. The failure is initiated at microscopical defects presumingly in the interface. The circumferential propagation of interface cracks starting at microdefects in unidirectional plies under transverse loading is studied using a representative volume element. First a linear elastic fracture mechanical analysis of interface cracks in a carbon fiber reinforced epoxy resin is performed by calculating the mixed mode energy release rate using the virtual crack closure method. The influence of the fiber spacing is studied by varying the fiber volume fraction. The total energy release rate rapidly grows after crack initiation indicating an unstable crack propagation. The first phase is dominated by mode I. The mode II energy release rate starts slightly delayed but surpasses the mode I part after a short crack length. By increasing the fiber volume fraction the maximum of the energy release rate shifts to smaller crack angles. T2 - ECCM17 CY - Munich, Germany DA - 27.06.2016 KW - fracture mechanics KW - interface crack KW - plasticity PY - 2016 AN - OPUS4-36906 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - 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 T2 - Proceedings of the 17th European Conference on Composite Materials 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 T2 - Proceedings of ICMFF11 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 T1 - Fracture on microscale of fiber reinforced composites N2 - Failure of composite materials is initiated by fracture processes on microscale, especially by interfacial debonding. Failure processes taking place on microscale are studied by single fiber experiments. This is, single fibers embedded in tensile specimen are loaded under various off-axis angles. Starting at microdefects interface cracks propagate circumferentially as well as longitudinally, depending on the loading angle. In addition, finite element simulations of interfacial crack propagation around single fibers as well as fibers embedded in a hexagonal composite are shown based on linear elastic fracture mechanics. The course of the energy release rate is given in dependence of the fiber volume fraction. T2 - Seminar CY - Imperial College, London, UK DA - 12.10.2016 KW - Composites KW - Fracture surfaces KW - Micromechanics KW - Epoxy resin PY - 2016 AN - OPUS4-37853 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 T2 - IOP Conf. Series: Materials Science and Engineering 139 (2016) 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 - TY - CONF A1 - Marotzke, Christian A1 - Feldmann, Titus T1 - Failure on microscale of epoxy resin and composites - limits of continuum mechanical analysis on micro- and nanoscale N2 - The problems of the limits of continuum mechanics are shown on some examples. The fiber-matrix debonding and subsequent crack propagation in fiber reinforced composites is studied. While Finite Element Analyses predict clear crack surfaces, either following the interface or bridging to the neighbouring fiber forming planes, the actual surfaces are very cliffy. Due to the much larger fracture surfaces and the completely different stress states on the cliffy fracture surfaces the continuum mechanical prediction is far from the actual local behaviour. The phenomenon of local high stresses which re much higher than the macroscopically measured strength of the material is also encountered in general fracture mechanics. The scale dependency of materials is shown on indentation tests conducted on different scales. From a continuum mechanical point of view it makes no difference if the indentation test is performed on a nano-, micro- or macroscale, because it is a matter of self-similarity. However, in nano- or microindentation tests on a pure polymer using e.g. a Berkovic indentor, the extremely high stress concentrations arising at the indentor tip are domination more or less the whole region around the indentor. In case of a macroscopical test, this zone covers only a small part of the material loaded by the indentor. Accordingly, the results of the different test cannot be scaled up. T2 - Second International Symposium on Directions in Damage and Durability of Composite Materials CY - Venedig, Italy DA - 18.06.2016 KW - continuum mechanics KW - fracture mechanics KW - epoxy resin KW - plasticity KW - large deformations PY - 2016 AN - OPUS4-37857 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Prewitz, Marc A1 - Müller, Ralf A1 - Marotzke, Christian A1 - Holtappels, Kai T1 - Characterization of glass capillary storage modules considering permeability and mechanical stress via finite elements N2 - Glass capillaries are potential candidates for long term hydrogen storage under high pressure. Burst pressure strongly drops with surface damaging, a polymer coating is needed. The aim is to study stress distribution within single coated glass capillaries sealed to metal fittings T2 - 88. Glastechnische Tagung DGG – ACerS GOMD 2014 CY - Aachen, Germany DA - 25.05.2014 KW - Burst test KW - Hydrogen storage KW - Polymer coating PY - 2014 AN - OPUS4-35784 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -