Experimental and numerical investigation of the properties of the fiber/matrix-interface of CFRP using model composites

Abstract

Experimental and numerical investigation of the properties of the fiber/matrix-interface of CFRP using model composites In this study, a novel approach to characterize the fiber/matrix-interface properties under transverse tensile loading of carbon fiber reinforced epoxy is presented. A single-fiber specimen concept for tensile testing perpendicular to the fiber is developed. Using the novel specimen concept, the interfacial failure is observed and the relevant variables describing the problem are extracted from the results. Under transversal tension, matrix has undergone significant plastic deformation prior to the interface failure. It is also found, that interfacial failure can be prematurely induced by plastic shear bands which initiated at flaws and other irregularities. Experimentelle und numerische Untersuchung der Faser/Matrix-Grenzflächeneigenschaften von CFK mit Modellverbunden In dieser Studie wird ein neuartiger Ansatz zur Charakterisierung der Faser/Matrix-Grenzflächeneigenschaften von kohlefaserverstärkten Epoxidharzen unter Querzugbelastung vorgestellt. Es wird ein Einzelfaser-Probenkonzept für die Zugprüfung senkrecht zur Faser entwickelt. Mit dem neuartigen Probenkonzept wird das Grenzflächenversagen beobachtet und die relevanten Kennwerte extrahiert. Unter Querspannung hat sich die Matrix vor dem Versagen der Grenzfläche stark plastisch verformt. Es wird auch festgestellt, dass Grenzflächenversagen vorzeitig durch plastische Scherbänder hervorgerufen werden kann, die bei Fehlstellen und anderen Unregelmäßigkeiten ausgelöst werden.

Calculation of the macroscopic mechanical properties of polyamide 6.6 underwater influence using molecular dynamics simulations, hyperelastic material modeling of the amorphous fraction, and homogenization schemes

“…The water uptake and the swelling of the specimens is measured after 24, 48, 72, 96, and 120 days of conditioning. The measurements for the specimens conditioned at norm conditions (23°C, 50% relative humidity) are shown in Figure 12 22,23 …”

“…0.03–0.06%. Afterwards, tensile test specimen according to type 1A of DIN EN ISO 527‐2 are produced in an Ergotech 80/420–310 injection molding machine from Sumitomo (SHI) Demag Plastics Machinery GmbH, Schwaig, Germany, with the following molding settings 22,23 :…”

“…The strain rate is 1 mm/min for strains less than 0.25% and 50 mm/min for larger strains. The deformation of the specimens is measured using an optical measurement system from Limess Messtechnik & Software GmbH, Krefeld, Germany using digital image correlation and tracking with a Marlin F‐146 B/C Camera from Allied Vision Technologies, Stadtroda, Germany 22,23 …”

“…A media concentration of 10.65 wt% corresponds to the simulation cell with 75 water molecules and is close to the maximum measured media concentration 22,23 . All simulation cell geometries are refined according to energy minimization using the Forcite geometry optimization module of Materials Studio .…”

“…In order to determine the degree of crystallization and the water concentration in polyamide 6.6 after different conditioning times, tensile specimens are injection molded and conditioned 22,23 . The degree of crystallization is determined using differential scanning calorimetry (DSC), while the media concentration is measured by weighting of the conditioned specimens.…”