TY - CONF A1 - Marotzke, Christian A1 - Feldmann, Titus T1 - Failure of composites under transverse loading - a fracture mechanical approach N2 - The failure of fiber reinforced composites under transverse loading is investigated on a representative volume element. The volume element is composed of a twelve fiber hexagonal array. The debonding of the central fiber is studied under transverse shear as well as under transverse compressive loading by calculating the mode I and mode II part of the energy release rate. The initiation of failure is assumed to take place at the location of maximum tensile or maximum shear stresses, respectively. In order to determine the failure initiation point, the stress field in the interface before crack initiation is calculated. T2 - ECCM15 - 15th European conference on composite materials CY - Venice, Italy DA - 2012-06-24 KW - Composites KW - Failure criteria KW - Fracture KW - Debonding KW - Fracture toughness KW - Interface PY - 2012 SN - 978-88-88785-33-2 SP - 1 EP - 7(?) AN - OPUS4-26450 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian A1 - Feldmann, Titus T1 - Fracture mechanics of composite plies on microscale N2 - The determination of the strength and the failure behaviour of fiber reinforced composites is a complex task. This is mainly due to the anisotropy and the inhomogeneiety of the material on the microscale. The strength or the fracture toughness of the interface between fiber and matrix is the key factor controlling the failure process on microscale, especially under loads transverse to the fiber axes. The ultimate failure of a laminate is a complex process consisting of a large number of different subprocesses. Due to its highly dynamic nature on one hand and the microscopical scale on the other it is not possible to observe the ultimate failure directly or even to analyse it theoretically. However, long before ultimate failure occurs a large number of elementary failure processes take place in a rather static manner or at least at low crack Propagation speed. T2 - ICCM19 - 19th International conference on composite materials CY - Montreal, Canada DA - 28.07.2013 KW - Fracture mechanics KW - Laminate KW - Interface KW - Debonding KW - Energy release rate PY - 2013 SP - 5354 EP - 5363 AN - OPUS4-28913 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian A1 - Feldmann, Titus T1 - Failure of epoxy resins and composites under multiaxial loads N2 - The failure of laminates is originated in plies loaded transverse to the fiber direction, e.g. in the 90° ply of a cross ply laminate. The initiation of failure is due to the debonding of individual fibers At some point the interface crack kinks into the matrix and propagates towards the inter-face of the neighbouring fiber. The cracks then continue propagating through the full ply. The interface failure obviously is the dominating process of the failure of plies in high fiber volume fraction composites. Several authors investigated the interfacial crack propagation on model systems. First, Varna and Paris studied the debonding process on a single fiber embedded in pure matrix under transverse ten-sion by fracture mechanical analyses. Correa and Paris performed experimental as well as numerical studies by calculating the mixed mode energy release rate under different loading conditions. These analyses were extended to fibers surrounded by a composite material by the present authors. Among others, Comninou as well as Sun and Jih have shown that the separation into a mode I and mode II energy release rate is not universal but the mixed mode ratio depends on the length of the crack increment. Comninou developed a solution of an interface crack between dissimilar media which reveals the even a small contact zone is found near the crack tip. As a result, the mode I part of the energy release rate vanishes because no opening of the crack takes place. The contact zone, however, is extremely small. If these mathematical phenomena, however, are relevant for physical problems is not verified. T2 - Thermosets 2013 - 3rd International conference on thermosets CY - Berlin, Germany DA - 18.09.2013 KW - Fracture mechanics KW - Laminate KW - Interface KW - Debonding KW - Energy release rate PY - 2013 SN - 978-3-00-043394-8 SP - 83 EP - 86 AN - OPUS4-29164 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian A1 - Feldmann, Titus ED - Milazzo, A. ED - Aliabadi, M. H. T1 - Fracture mechanics of fiber-matrix interfaces in composites under transverse loading T2 - FDM 2013 - 12th International conference on fracture and damage mechanics CY - Sardinia, Italy DA - 2013-09-17 KW - Fracture mechanics KW - Laminate KW - Interface KW - Debonding KW - Energy release rate PY - 2013 SN - 978-3-03785-830-1 SN - 1013-9826 SN - 1662-9809 SN - 1662-9795 SP - 433 EP - 436 PB - Trans Tech Publications AN - OPUS4-29142 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Epishin, A. A1 - Fedelich, Bernard A1 - Link, T. A1 - Feldmann, Titus A1 - Svetlov, I.L. T1 - Pore annihilation in a single-crystal nickel-base superalloy during hot isostatic pressing: Experiment and modelling N2 - Pore annihilation during hot isostatic pressing (HIP) was investigated in the single-crystal nickel-base superalloy CMSX-4 experimentally by interrupted HIP tests at 1288 °C/103 MPa. The kinetics of pore annihilation was determined by density measurement and quantitative metallography. Transmission electron microscopy of a HIPed specimen showed that the pores shrink via dislocation movement on octahedral glide planes. Theoretically pore closure under HIP condition was modelled by the finite element method using crystal plasticity and large strain theories. The modelling gives a similar kinetics of pore annihilation as observed experimentally, however somewhat higher annihilation rate. KW - Nickel based superalloys KW - Electron microscopy KW - Crystal plasticity KW - Bulk deformation KW - Finite element method PY - 2013 U6 - https://doi.org/10.1016/j.msea.2013.08.034 SN - 0921-5093 SN - 1873-4936 VL - 586 SP - 342 EP - 349 PB - Elsevier CY - Amsterdam AN - OPUS4-29418 LA - eng 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 - Feldmann, Titus A1 - Marotzke, Christian T1 - Fracture of fiber reinforced materials under off-axis loading T2 - APCFS - Asian-Pacific Conference on Fracture and Strength 2014 CY - Sydney, Australia DA - 2014-12-09 PY - 2014 AN - OPUS4-32318 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian A1 - Feldmann, Titus T1 - Fracture of fiber reinforced materials under off-axis loading N2 - The failure behaviour of unidirectional plies tested under off-axis loading is studied. The stress distribution occurring in standard off-axis tests is briefly discussed. The different failure modes, this is, pure fiber breakage, pure inter fiber failure as well as a superposition of both is analysed based on test data and fracture patterns. The large difference of the failure load depending on the failure mode at small off-axis angles is studied by comparison of a short and a long 3° off-axis angle specimen. T2 - APCF/SIF-2014 - Asian-Pacific conference on fracture and strength / International conference on structural integrity and failure - Recent advances in structural integrity analysis CY - Sydney, Australia DA - 09.12.2014 KW - Debonding KW - Off-axis strength KW - Fracture mechanics KW - Composite materials PY - 2014 SN - 978-0-08-100203-2 SN - 978-0-08-100225-4 SP - 351 EP - 355 PB - Elsevier AN - OPUS4-32324 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Marotzke, Christian A1 - Feldmann, Titus T1 - Fracture mechanics on microscale of composite plies under transverse loading N2 - The energy release rate delivered during the debonding of a fiber inside a composite ply is analysed using a representative volume element. Two different fiber volume fractions are studied by a linear elastic fracture mechanical analysis by using the finite element method. The dependency of the mixed mode energy release rate on the length of the crack increment is analysed. It is shown that the same general behaviour found in case of a straight Interface crack is valid also for circular cracks. As a result the discrimination of the energy release rate into mode I and mode II portions is questionable. T2 - ECCM16 - 16th European conference on composite materials CY - Seville, Spain DA - 22.06.2014 KW - Composite KW - Interface crack KW - Energy release rate KW - Mode mixity PY - 2014 SN - 978-84-616-9798-4 SP - 0472-1 EP - 0472-8 AN - OPUS4-31133 LA - eng 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 -