This paper aims to propose a novel approach to assess the multi-crack behavior of layered fiber-polymer composites. The Compliance and R-curves generated from this novel approach were useful to understand the multiple delamination process, enabling to evaluate separately the strain energy release rate (SERR) related to each crack. A cohesive zone model was developed to simulate the failure process zone of three parallel cracks in web-flange junction (WFJ) specimens extracted from a pultruded bridge deck system subjected to transverse bending. The fracture parameters estimated based on the proposed approach led to a good agreement between the numerical model and the experiments in terms of load vs. displacement curves. Moreover, it was possible to observe that the formation of new cracks may lead to a significant drop on the R-curve, due to the closure of the former cracks.

@en

This paper aims to propose a novel approach to assess the multi-crack behavior of layered fiber-polymer composites. The Compliance and R-curves generated from this novel approach were useful to understand the multiple delamination process, enabling to evaluate separately the strain energy release rate (SERR) related to each crack. A cohesive zone model was developed to simulate the failure process zone of three parallel cracks in web-flange junction (WFJ) specimens extracted from a pultruded bridge deck system subjected to transverse bending. The fracture parameters estimated based on the proposed approach led to a good agreement between the numerical model and the experiments in terms of load vs. displacement curves. Moreover, it was possible to observe that the formation of new cracks may lead to a significant drop on the R-curve, due to the closure of the former cracks.

@en

Many recent works have shown that the capacity of pultruded glass fiber-polymer structural members is governed by interlaminar failure. However, there is still a lack of information regarding the fracture properties associated and the best techniques to be adopted. This paper aims to propose a testing methodology and to evaluate the interlaminar fracture of pultruded glass fiber-polymer specimens extracted from a composite bridge deck system. Both Modes I and II were investigated, through Double Cantilever Beam (DCB) and End-Loaded-Split (ELS) tests, respectively. The starter crack (or initial separation) was introduced via a water jet machine and the crack length was measured with the video extensometer technique. In all, nine different methods were applied to obtain the fracture toughness properties. The results are discussed and compared with 2D non-linear finite element models, where the cohesive zone model (CZM) approach was used. The Modified Beam Theory method (MBT_ASTM) presented the best results for crack propagation in Mode I, whereas differences lower than 1% from experiments were obtained when using the Corrected beam theory using effective crack length (CBTE) and the Experimental compliance method (EMC) methods for Mode II.

@en

Challenges of reliable prediction of resistance of bonded joints lie in the complexity of stress concentrations, multiple crack paths, mode-mixity and sudden crack propagation. The new Technical Specification for Design of fibre-polymer composite structures (TS) is bridging this gap by providing comprehensive sets of design recommendations and analyses to be used for the verification of adhesive joints. Two design approaches in the TS, based on stress analysis and fracture mechanics, are summarized and basic design assumptions on allowed failure conditions and partial factors in relation to execution and maintenance are highlighted. The application of the design recommendations is shown on the example of determining the design value and the ultimate resistance of a simple double lap joint. FE models built in Abaqus are used to analyse stress concentrations and crack initiation and propagation based on material level experiments. Variability of the material properties are taken into account through partial safety factors. Joint resistances obtained by the stress-based approach and fracture-mechanics approach are compared. @en

It was essential in the European Technical Specification for the Design of Fibre- Polymer Composite Structures (prCEN/TS 19101) to provide an Ultimate Limit State design procedure for a failure criterion for multi-ply laminates subjected to in-plane combined actions, which will give a generically applicable and a simple design procedure. This paper will discuss the rationale for the project team (of Working Group 4 to CEN/TC250) deciding that the resistance formula is to satisfy a linear interaction failure criterion. @en

This paper aims to present an experimental investigation on the behavior of web-flange junctions (WFJs) rotational stiffness of pultruded fiber-reinforced polymer composites (FRP). Channels and I-sections were tested using a simple set-up, which was developed in order to experimentally characterize the junctions in a direct manner. The Digital Image Correlation (DIC) technique was used, allowing overall deflections and relative rotations between web and flange to be monitored. The WFJs' imperfections were analyzed through an optical microscope and correlated with the cracks' formation. Further, damage thresholds are identified using available stress equations for curved composite members and lower bound functions are proposed to simulate the junction stiffness retention. Finally, two Equations are developed in order to analytically predict pultruded junctions' rotational stiffness per unit of width. In general, the theoretical and experimental results agreed fairly well, with a maximum difference of 24% for I-sections and 38% for channels.

@en

The energy resolution of the conventional way of measuring a small change in a phonon dispersion curve using neutron scattering is restricted by the relatively coarse intrinsic resolution ellipsoid of the neutron triple-axis spectrometer (TAS). By implementing inelastic neutron spin echo on the host TAS using the Larmor precession of the neutron spin, the energy resolution of such measurements can be further improved without reducing the resolution ellipsoid. Measurements of the temperature-dependent phonon energy change are demonstrated using superconducting magnetic Wollaston prisms at the HB-1 instrument of the High-Flux Isotope Reactor at Oak Ridge National Laboratory, and the achievable resolution is <10 µeV.

@en

Larmor precession has been used in the past in neutron spin-echo and neutron depolarisation. In the last decade, interest has been revived in the inclined front and end faces of the precession regions combined with the neutron-resonance spin-echo (NRSE) technique. Various techniques based on these inclined faces have been developed, such as spin-echo, small-angle neutron scattering (SESANS), off-specular neutron reflectometry using SESANS and high-resolution diffraction using Larmor precession. An overview will be given of the various state-of-the-art techniques.

@en