TY - CONF A1 - Marotzke, Christian T1 - Limits in the determination of mechanical properties of composites by off-axis tests T2 - European SAMPE Conference CY - Paris, France DA - 2014-03-10 PY - 2014 AN - OPUS4-30337 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian A1 - Feldmann, Titus T1 - Limits in the determination of mechanical properties of composites by off-axis tests N2 - Off-axis tests are widely used for the determination of the anisotropic mechanical properties of composite materials, this is, the longitudinal E-modulus and the strength. The mechanical properties are evaluated from the test data under idealising assumptions such as homogeneity of the material as well as a homogeneous stress distribution. In real off-axis tests, however, significant deviations from the idealising assumptions are present. The reduction of the accuracy of the results strongly depends on the off-axis angle. In this paper a series of off-axis tests is analysed. The stresses on potential failure plane are calculated by finite element analyses. By varying the geometrical parameters it is shown how small deviations from the ideal case influence the measured elastic constants and the strength. Especially at low off-axis angles the mechanical properties strongly vary with the angle. In addition, fracture surfaces for different shear/normal stress combinations are studied and typical phenomena are identified. T2 - SEICO 14 - SAMPE Europe 35th International conference and forum CY - Paris, France DA - 10.03.2014 KW - Off-axis test KW - Composites KW - Strength KW - E-modulus PY - 2014 SN - 978-90-821727-0-6 IS - Session 5B SP - 293 EP - 300 AN - OPUS4-30376 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian T1 - Fracture mechanics on microscale of composite plies under transverse loading T2 - ECCM 16 - 16th European Conference on Composite Materials CY - Seville, Spain DA - 2014-06-22 PY - 2014 AN - OPUS4-31012 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian T1 - Fracture Processes in Composites under Off-Axis Loading T2 - 28. Workshop Composite Forschung in der Mechanik CY - Paderborn, Deutschland DA - 2015-12-09 PY - 2015 AN - OPUS4-35300 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian T1 - Limits of the continuum mechanical treatment of problems on micro- and nanoscale. T2 - COMPO 2014 CY - Rehovot, Israel DA - 2014-04-28 PY - 2014 AN - OPUS4-30639 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian A1 - Feldmann, Titus ED - Thomson, Ole T1 - Characterisation of failure processes of composite plies under transverse loading 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 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 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 - Composites KW - Failure KW - Energy release rate PY - 2016 AN - OPUS4-36746 LA - deu 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 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 - Marotzke, Christian T1 - Failure processes of fiber reinforced composites under off-axis loading T2 - ICM 12 - 12th International Conference on the Mechanical Behavior of Materials CY - Karlsruhe, Germany DA - 2015-05-10 PY - 2015 AN - OPUS4-33183 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian T1 - Identification of material properties of epoxy resins by micro- and nanoindentation tests T2 - GUC Workshop Materials Research and Industry CY - Berlin, Germany DA - 2014-05-13 PY - 2014 AN - OPUS4-30663 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian T1 - Limits of continuum mechanics in analysing failure processes in fiber reinforced composites on microscale T2 - Composite Damage Workshop VI CY - Gerona, Spain DA - 2014-09-08 PY - 2014 AN - OPUS4-31346 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian T1 - Interface cracks on microscale in composites T2 - ECF20 - 20th European Conference on Fracture CY - Trondheim, Norway DA - 2014-06-30 PY - 2014 AN - OPUS4-31017 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -