The Experts below are selected from a list of 162 Experts worldwide ranked by ideXlab platform

Stephen R. Hallett - One of the best experts on this subject based on the ideXlab platform.

  • experimental study on delamination migration in multidirectional laminates under mode ii static and fatigue loading with comparison to mode i
    Composite Structures, 2018
    Co-Authors: Yu Gong, Bing Zhang, Supratik Mukhopadhyay, Stephen R. Hallett
    Abstract:

    Abstract This paper presents an experimental investigation to better understand the mechanisms of delamination migration in multidirectional End Loaded Split (ELS) specimens. A stacking sequence susceptible to delamination migration was selected for this study and subjected to pure mode II static and fatigue loading. The static and fatigue results gave comparable migration mechanisms, however, differences were noted regarding the damage sequence, the fracture surface , the migration angle and the horizontal distances of migrated location to the front of pre-crack. Scanning Electron Microscopy (SEM) results indicated that fibre imprints and cusps were two dominant micro-features on the fracture surfaces for all specimens. Interactions between delamination and ply Splits were observed and confirmed by X-ray CT scanning. Furthermore, comparison was made to understand the effects of loading modes (mode I and II) on delamination migration.

  • cohesive element formulation for z pin delamination bridging in fibre reinforced laminates
    International Journal of Solids and Structures, 2018
    Co-Authors: Galal F A Mohamed, Mehdi Yasaee, Gabriella Allegri, Stephen R. Hallett
    Abstract:

    Abstract Z-pins are an effective method of reinforcing laminated composite materials for resisting the propagation of delamination. In this paper, a novel numerical method combines the classical cohesive finite element (FE) method with a semi-analytical z-pin crack bridging model. Special purpose cohesive elements, in which the generalized traction-displacement characteristics are provided by the semi-analytical model z-pin bridging map, are implemented in macro-scale FE models. This cohesive element offers the flexibility to employ two cohesive laws concurrently for prediction of delamination propagation, for both the pinned and unpinned behaviour. Its efficacy is evaluated by the simulation of double cantilever beam (DCB), mixed-mode bend (MMB), and pure mode II End-Loaded Split (ELS) fracture tests at 2% z-pin areal density. The numerical results in terms of load-deflection predictions agree well with experiments. The different simulations were all performed using a single set of input parameters derived from single z-pin tests with no fitting factors.

  • cohesive element formulation for z pin delamination bridging in fibre reinforced laminates
    International Journal of Solids and Structures, 2018
    Co-Authors: Galal F A Mohamed, Mehdi Yasaee, Gabriella Allegri, Stephen R. Hallett
    Abstract:

    Abstract Z-pins are an effective method of reinforcing laminated composite materials for resisting the propagation of delamination. In this paper, a novel numerical method combines the classical cohesive finite element (FE) method with a semi-analytical z-pin crack bridging model. Special purpose cohesive elements, in which the generalized traction-displacement characteristics are provided by the semi-analytical model z-pin bridging map, are implemented in macro-scale FE models. This cohesive element offers the flexibility to employ two cohesive laws concurrently for prediction of delamination propagation, for both the pinned and unpinned behaviour. Its efficacy is evaluated by the simulation of double cantilever beam (DCB), mixed-mode bend (MMB), and pure mode II End-Loaded Split (ELS) fracture tests at 2% z-pin areal density. The numerical results in terms of load-deflection predictions agree well with experiments. The different simulations were all performed using a single set of input parameters derived from single z-pin tests with no fitting factors.

  • Delamination resistance of composites using inclined Z-pins
    2015
    Co-Authors: Beene M'membe, Mehdi Yasaee, Stephen R. Hallett, Sam Gannon, Ivana K. Partridge
    Abstract:

    This study explores the behaviour of inclined Z-pins inserted in End Loaded Split (ELS) specimens at areal densities of 0.22% and 0.40%. The study has shown an increase in the fracture toughness when Z-pins are better aligned with the load vector (inclined) compared to the conventional, orthogonally inserted Z-pins. Brittle, catastrophic failure occurs when the inclined Z-pins are misaligned with the load vector. Given the difficulty in predicting localised load vectors in complex structures, specimens with ±θ configuration are tested and compared to conventional non-inclined Zpin configurations. The results for the areal densities tested in this study show minimal differences in delamination resistance between the two configurations. However, there is some evidence to suggest that at high areal densities, the ±θ configuration is likely to produce higher GIIC values compared to the conventional non-inclined Z-pin configuration.

Giovanni P Terrasi - One of the best experts on this subject based on the ideXlab platform.

Sung R. Choi - One of the best experts on this subject based on the ideXlab platform.

  • An Investigation of the End-Notched Flexure and End-Loaded Split Tests Applied to the Mode II Interlaminar Fracture of a SiC/SiC Ceramic Matrix Composite
    Journal of Engineering for Gas Turbines and Power, 2020
    Co-Authors: Michael J. Presby, Gregory N. Morscher, Cody Godines, Amir Eftekharian, Jalees Ahmad, Frank Abdi, Manigandan Kannan, Sung R. Choi
    Abstract:

    Abstract Delamination is a common failure mode observed in ceramic matrix composites (CMCs) and occurs as a result of applied interlaminar tensile and shear stresses exceeding the interlaminar strength. As CMCs are further implemented into aero engines, the need to understand their interlaminar failure becomes increasingly important. While significant contributions have been made toward understanding the mode I fracture toughness of CMCs, limited work exists on mode II. Several test methods for measuring the mode II fracture toughness have been proposed in the literature, namely, the end-notched flexure (ENF) and the End-Loaded Split (ELS) tests. This work investigates the mode II fracture toughness of a melt-infiltrated SiC/SiC CMC at ambient temperature using the ENF and ELS test methods. Acoustic emission (AE), direct current potential drop (DCPD), and digital image correlation (DIC) are implemented as health monitoring techniques to monitor crack initiation and propagation. Results show reasonable correlation between the two test methods and that the ELS test method is better suited for characterizing R-curve behavior.

  • An Investigation of the End-Notched Flexure and End-Loaded Split Tests Applied to the Mode II Interlaminar Fracture of a SiC/SiC Ceramic Matrix Composite
    Volume 6: Ceramics; Controls Diagnostics and Instrumentation; Education; Manufacturing Materials and Metallurgy, 2019
    Co-Authors: Michael J. Presby, K. Manigandan, Gregory N. Morscher, Cody Godines, Amir Eftekharian, Jalees Ahmad, Frank Abdi, Sung R. Choi
    Abstract:

    Abstract Delamination is a common failure mode observed in ceramic matrix composites (CMCs) and occurs as a result of applied interlaminar tensile and shear stresses exceeding the interlaminar strength. As CMCs are further implemented into aero engines the need to understand their interlaminar failure becomes increasingly important. While significant contributions have been made toward understanding the mode I fracture toughness of CMCs, limited work exists on mode II. Several test methods for measuring the mode II fracture toughness have been proposed in literature, namely the end-notched flexure (ENF) and the End-Loaded Split (ELS) tests. This work investigates the mode II fracture toughness of a melt-infiltrated SiC/SiC CMC at ambient temperature using the ENF and ELS test methods. Acoustic emission (AE), direct current potential drop (DCPD), and digital image correlation (DIC) are implemented as health monitoring techniques to monitor crack initiation and propagation. Results show reasonable correlation between the two test methods and that the ELS test method is better suited for characterizing R-curve behavior.

Andreas J. Brunner - One of the best experts on this subject based on the ideXlab platform.

  • mode ii fatigue delamination resistance of advanced fiber reinforced polymer matrix laminates towards the development of a standardized test procedure
    International Journal of Fatigue, 2013
    Co-Authors: Andreas J. Brunner, Steffen Stelzer, Gerald Pinter, Giovanni P Terrasi
    Abstract:

    Abstract Delamination resistance testing of fiber-reinforced polymer–matrix laminates under fatigue loads is important for materials development and structural design. Mode II in-plane shear fatigue test development using three-point bending end-notched flexure (3-ENF) and two-point bending End-Loaded Split (ELS) set-ups is performed in a round robin. Effects of specimen restraint observed earlier in ENF tests are confirmed and preliminary data indicate differences between the two set-ups, if simple beam theory or experimental compliance analyses are applied. Possible reasons for the observed disagreement are discussed.

  • Mode II fatigue delamination resistance of advanced fiber-reinforced polymer–matrix laminates: Towards the development of a standardized test procedure
    International Journal of Fatigue, 2013
    Co-Authors: Andreas J. Brunner, Steffen Stelzer, Gerald Pinter, Giovanni P Terrasi
    Abstract:

    Abstract Delamination resistance testing of fiber-reinforced polymer–matrix laminates under fatigue loads is important for materials development and structural design. Mode II in-plane shear fatigue test development using three-point bending end-notched flexure (3-ENF) and two-point bending End-Loaded Split (ELS) set-ups is performed in a round robin. Effects of specimen restraint observed earlier in ENF tests are confirmed and preliminary data indicate differences between the two set-ups, if simple beam theory or experimental compliance analyses are applied. Possible reasons for the observed disagreement are discussed.

  • Mode II fracture testing of composites: a new look at an old problem
    Engineering Fracture Mechanics, 2006
    Co-Authors: Bamber R.k. Blackman, Andreas J. Brunner, J. G. Williams
    Abstract:

    Abstract A number of technical issues have slowed the progress towards an agreed mode II test protocol for composite laminates and perhaps the most important of these has concerned the difficulty in measuring crack length during the test. In this paper, we extend a previous analysis which was developed for mode I delamination cases where significant bridging and micro-cracking occurred. The approach utilises an effective crack length and if successful, may eliminate the need to measure this parameter experimentally. To accommodate the new approach, an existing test protocol based on the End-Loaded Split (ELS) method has been revised and some data measured using the scheme is presented. This includes some initial results measured in a round-robin activity co-ordinated by a technical committee of the European Structural Integrity Society (ESIS). A number of materials are examined with a view to determining the utility of the ‘crack length independent’ approach.

Irene Fernandez Villegas - One of the best experts on this subject based on the ideXlab platform.

  • interlaminar fracture toughness of 5hs carbon peek laminates a comparison between dcb els and mandrel peel tests
    Polymer Testing, 2018
    Co-Authors: Francisco Sacchetti, Wouter Johannes Bernardus Grouve, Laurent Warnet, Irene Fernandez Villegas
    Abstract:

    The present work focuses on the applicability of the mandrel peel test to quantify the interlaminar fracture toughness of 5 harness satin woven fabric Carbon/PEEK composites. For this purpose, the Mandrel Peel (MP) test was compared to the Double Cantilever Beam (DCB) and End-Loaded Split (ELS) test in terms of experimental procedure and results obtained. The interlaminar toughness of the 5 harness Carbon/PEEK was measured both parallel and perpendicular to the predominant fibre direction at the interface. While stable crack propagation was observed in the ELS test, unstable crack propagation (stick-slip) was observed during both the DCB and the mandrel peel tests. In the case of the mandrel peel test, however, the unstable propagation was immediately arrested by the mandrel, limiting the instability and providing numerous crack re-initiation values per unit of crack length. This effect is expected to increase the statistical relevance of a single test and thereby to increase the reliability of the measured values as compared to DCB tests. A fractographic analysis was performed to study the nature of the crack propagation for the different testing techniques. The mandrel peel test was found to be a potentially plausible alternative to the DCB test for woven fabric reinforced composites.

  • Interlaminar fracture toughness of 5HS Carbon/PEEK laminates. A comparison between DCB, ELS and mandrel peel tests
    Polymer Testing, 2018
    Co-Authors: Francisco Sacchetti, Wouter Johannes Bernardus Grouve, Laurent Warnet, Irene Fernandez Villegas
    Abstract:

    The present work focuses on the applicability of the mandrel peel test to quantify the interlaminar fracture toughness of 5 harness satin woven fabric Carbon/PEEK composites. For this purpose, the Mandrel Peel (MP) test was compared to the Double Cantilever Beam (DCB) and End-Loaded Split (ELS) test in terms of experimental procedure and results obtained. The interlaminar toughness of the 5 harness Carbon/PEEK was measured both parallel and perpendicular to the predominant fibre direction at the interface. While stable crack propagation was observed in the ELS test, unstable crack propagation (stick-slip) was observed during both the DCB and the mandrel peel tests. In the case of the mandrel peel test, however, the unstable propagation was immediately arrested by the mandrel, limiting the instability and providing numerous crack re-initiation values per unit of crack length. This effect is expected to increase the statistical relevance of a single test and thereby to increase the reliability of the measured values as compared to DCB tests. A fractographic analysis was performed to study the nature of the crack propagation for the different testing techniques. The mandrel peel test was found to be a potentially plausible alternative to the DCB test for woven fabric reinforced composites.