Abstract This article reports modeling techniques and results based on experimental Mode I characterization of a layered woven GFRP material with tufting reinforcement. Standard tuft and loop-less geometries are investigated on three different areal patterns to evaluate their effects on fracture resistance. The experiments reveal that tow/ply and tuft bridging phenomena are present during delamination. The numerical modeling comprises cohesive elements for tow/ply bridging and 1D connector elements for discrete tufts. The traction separation relations for the cohesive model are acquired using an inverse scheme based on strain measurements and the force-separation relations of tuft’s failure mechanisms from uniaxial pulling tests on a reference tufting pattern. Results show that tuft’s failure mechanism is strongly affected by tufting pattern and geometry while tow/ply bridging contributes 20–30% of the overall fracture energy. The energy absorbed by pull-out of loop-less tufts is approximately twice the fracture energy of standard ones with pull-out triggering much more extensive tow/ply bridging phenomena.
#1G. Pappas(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 8
#2Simon Joncas(École de technologie supérieure)H-Index: 10
Last. John Botsis(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 37
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Abstract This experimental study reports effect of tuft geometry i.e., standard tufts and loops milled-down, and tufting pattern on Mode I interlaminar fracture in a GFRP. Standard tufting geometry is responsible for an increase in fracture resistance by 3.5–6 times than the neat composite, depending on the areal pattern. Based on 5 mm squared tufting pattern on DCB specimens with a full-length release film at laminate mid-plane and non-tufted ones, the individual contribution to fracture of tuf...
Abstract A constitutive model for tufts bridging a mode I delamination is presented. The tuft is modelled as a rod, laterally supported by an elastic medium and clamped at both ends. A fracture mechanics approach is introduced to describe the progressive debonding of the tuft from the embedding laminate. The debonding model requires the identification of stiffness, strength and toughness properties, which depend both on the laminate/tuft architecture and the constituent materials. Such identific...
#1G. Pappas(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 8
#2Luis P. Canal(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 11
Last. John Botsis(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 37
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Abstract A detailed experimental-numerical study of large scale bridging during intralaminar fracture of AS4/PPS uniaxial thermoplastic composite is reported. Identification of bridging tractions is carried out using: (a) An inverse identification method based on quasi-distributed strain data from fiber Bragg gratings, FE modeling and optimization; both small and large displacements are considered in the simulations resulting in negligible differences between the bridging tractions and of about ...
A new finite modelling approach is presented to analyse the mode I delamination fracture toughness of z-pinned laminates using the computationally efficient embedded element technique. In the FE model, each z-pin is represented by a single one-dimensional truss element that is embedded within the laminate. Each truss is given the material, geometric and spatial properties associated with the global crack bridging traction response of a z-pin in the laminate; this simplification provides a comput...
#1G. Pappas(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 8
#2John Botsis(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 37
Abstract Fracture of carbon fiber reinforced polymers (CFRPs) is dominated by large scale fiber bridging which acts as a very important toughening mechanism. The objective of this paper is to investigate the intralaminar Mode I fracture in a unidirectional CFRP composite in double cantilever beam specimens with thickness H = 6, 10 and 14 mm with a symmetric intralaminar precrack introduced by a thin diamond wire saw. Optical fibers with 10 multiplexed Bragg grating sensors are glued onto the upp...
Abstract Fiber reinforced composites can develop large scale bridging upon mode I fracture. This toughening mechanism depends on the constituents and the geometry of the specimen, and is especially important in unidirectional laminates when fracture is parallel to the fibers. The mode I intralaminar fracture behavior of unidirectional carbon-epoxy laminates was investigated by means of a three-dimensional multiscale model based on an embedded-cell approach. A double cantilever beam specimen was ...
Abstract The influence of the material properties of z-pins on the mode I delamination properties of carbon–epoxy laminates is investigated. Improvements to the delamination fracture toughness and fatigue resistance of laminates reinforced in the through-thickness direction with z-pins made of metal (copper, titanium or stainless steel) or unidirectional carbon fibre composite is determined. Irrespective of the material, the z-pins are highly effective at increasing the fracture toughness and fa...
This paper presents a three-dimensional micro-mechanical finite element (FE) modelling strategy for predicting the mixed-mode response of single Z-pins inserted in a composite laminate. The modelling approach is based upon a versatile ply-level mesh, which takes into account the significant micro- mechanical features of Z-pinned laminates. The effect of post-cure cool down is also considered in the approach. The Z-pin/laminate interface is modelled by cohesive elements and frictional contact. Th...
Large scale bridging is an important toughening mechanism in composite laminates that depends on the specimen geometry as well as the constituent materials. In this work, an iterative approach is applied to identify the effect of specimen thickness on traction-separation behavior in the bridging zone. Double cantilever beam specimens (DCB) with embedded arrays of wavelength-multiplexed fiber Bragg grating (FBG) sensors are subjected to monotonic mode I fracture loading. As processed specimens wi...
Abstract A new micro-mechanical model is proposed for describing the bridging actions exerted by through-thickness reinforcement on delaminations in prepreg based composite materials, subjected to a mixed-mode (I–II) loading regime. The model applies to micro-fasteners in the form of brittle fibrous rods (Z-pins) inserted in the through-thickness direction of composite laminates. These are described as Euler–Bernoulli beams inserted in an elastic foundation that represents the embedding composit...
Traditional laminated composites have fibres oriented only in the in-plane of the laminate due to their manufacturing process, and are therefore very susceptible to transverse cracking and delamination from out-of-plane actions. Delamination can considerably reduce the load bearing capacity of a structure hence several reinforcement solutions, based on the principle to add out-of-plane reinforcement to the 2D fabric, have been explored to enhance the delamination resistance. However, the usual t...
Abstract A new type of fibre reinforced polymer composite is presented that uniquely combines high delamination resistance with crack closure properties via the use of tufted shape memory alloy (SMA) filaments. A carbon-epoxy laminate was tufted in the through-thickness direction using thin SMA filaments of Ni-Ti alloy (nitinol). The SMA tufts increase the mode I interlaminar fracture toughness of the laminate by forming a large-scale bridging process zone along the delamination crack. Following...
Abstract R-curve and traction-separation relation are commonly used to characterize the fiber bridging, which is significant toughening mechanism in composite laminates. Current investigations are mainly focused on unidirectional laminates. However, the dependence of the R-curve and traction-separation relation on the stacking sequence is still lack of comprehensive studies. Here, the effect of stacking sequence on the R-curve and traction-separation relation in unidirectional and multidirection...
#1G. Pappas(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 8
#2John Botsis(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 37
Abstract Traction-separation relations due to large scale bridging in composites are very important in modeling their fracture response. Several works demonstrated that such relations are dependent upon the specimen's stiffness and loading conditions. Experimental data and micromechanics of bridging suggested that, in addition to the crack opening displacement (COD), the local curvature can be used as an additional kinematic parameter to incorporate the stiffness dependence on traction-separatio...
Abstract Tufting is an ongoing technique to manufacture the 3-dimensional (3D) textile reinforcement for composites. The inserted tufting threads provide a good mechanical performance through-the-thickness of the final composite parts. However, the degradation of inserted tufting thread can be experienced during the tufting process. This degradation brings out the negative influence on the mechanical performance of the reinforced tufting thread and of the composite, which is not yet studied and ...
Abstract The mode I delamination behavior of a unidirectional glass-fiber reinforced polymer with a prototype elasto-plastic polyurethane matrix (GF/PU) was investigated and compared with that of glass/epoxy (GF/EP) using double cantilever beam specimens. Fracture resistance was assessed using experimental data based on the strain energy release rate (ERR), G , calculated by means of the modified compliance calibration, and the J -integral, calculated using the applied force and arm rotations me...
#2Hong-Yuan Liu(Center for Advanced Materials)H-Index: 32
Last. Xusheng Du(JNU: Jinan University)H-Index: 32
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An analytical model was developed to study the interlaminar fracture behaviour of polymer composite reinforced by carbon fibres grafted with carbon nanotubes. Delamination properties, such as load with displacement or crack (R-curve) and toughness with crack (GR-curve), can be obtained from this model. The bridging laws presented, based on the CNT pullout mechanism (CNT pullout from polymer matrix) and the CNT sword-in-sheath mechanism (CNT breakage), were incorporated into the proposed analytic...
Three-dimensional preforms have been developed in order to remedy and minimize the out-of-plane damage caused by 2D structures. Several researches have been done on more complex structures which ha...
#1G. Pappas(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 8
#2Simon Joncas(École de technologie supérieure)H-Index: 10
Last. John Botsis(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 37
view all 4 authors...
Abstract This experimental study reports effect of tuft geometry i.e., standard tufts and loops milled-down, and tufting pattern on Mode I interlaminar fracture in a GFRP. Standard tufting geometry is responsible for an increase in fracture resistance by 3.5–6 times than the neat composite, depending on the areal pattern. Based on 5 mm squared tufting pattern on DCB specimens with a full-length release film at laminate mid-plane and non-tufted ones, the individual contribution to fracture of tuf...
