Fracture Toughness Of CFRP Laminates Research Articles

Mode I interlaminar fracture toughness of CFRP laminates reinforced with short aramid fibers

Adhesive bonding has been applied successfully in many technologies. The short aramid fibers can be effectively embedded in interface layer wit adhesive-rich regions of the CFRP fabrics with carbon fibers oriented at 0° and 90° to form a strong pulling resistance. In this paper, the interface toughness of carbon fiber composite reinforced by aramid short fiber is studied based on the mode I crack growth test of double cantilever beam. The effort of the length and density of aramid short fiber on the interface toughness of carbon fiber composite are discussed. The test result shows that the best bonding strength is obtained at the condition of the aramid fibers with the length of 3 mm at the density of 24 g/m2. The ultimate load and the Mode I interlaminar fracture toughness are improved by 292.87% and 168.59%, respectively. The crack propagation path and fracture effect are analyzed and compared by Scanning Electron Microscopy (SEM) observations.

Effect of low melting temperature polyamide fiber-interlaced carbon fiber braid fabric on the mechanical performance and fracture toughness of CFRP laminates

Fracture toughness and epoxy matrix brittleness have been main issues in carbon/epoxy composites. Various studies have been reported to improve the fracture toughness and brittleness of the carbon/epoxy composites. Although conventional method such as toughened epoxy matrix dissolving method, interleaving with a thermoplastic interlayer method, incorporating with a thermoplastic particles method improve the fracture toughness and brittleness of the carbon/epoxy composites, there have been no significant improvement. Therefore, in this study, due to improve the fracture toughness and brittleness of the carbon/epoxy composites, applied the carbon fiber/low melting temperature polyamide fiber co-braid fabric. In addition, the toughened effect of carbon fiber co-braid fabric with low melting temperature polyamide fiber and high melting temperature polyamide fiber were investigated. The carbon/epoxy composites manufactured by carbon fiber/low melting temperature polyamide fiber co-braid fabric, the fracture toughness significantly improved about 293% compared to the pristine specimens.

Evaluation for Interlaminar Fracture Toughness of CFRP Laminates with Mesh of Different Opening Area

Evaluation for Interlaminar Fracture Toughness of CFRP Laminates with Mesh of Different Opening Area

Comparative study on prediction of fracture toughness of CFRP laminates from size effect law of open hole specimen using cohesive zone model

Carbon fibre reinforced polymer laminates (CFRPs) are widely used in the aerospace industry. However, the longitudinal fracture toughness of this composite material is a major factor that causes its failure. Here, physical linear and exponential softening laws are used to predict the fracture toughness of CFRPs. The model estimates the predicted strength of an open hole specimen of the material by using the cohesive law and the limiting value of the critical crack opening and unnotched strength obtained using a simple tension test. The critical crack opening is calculated based on a thickness formula. The model results are in good agreement with the experimental results, with errors of 6.39% and 11.29% for the linear and exponential cohesive laws, respectively.

ダブルラップジョイント型試験片による CFRP のモード II 破壊じん性値評価の提案

ダブルラップジョイント型試験片による CFRP のモード II 破壊じん性値評価の提案

Experimental investigation of CNT effect on curved beam strength and interlaminar fracture toughness of CFRP laminates

High mechanical properties and light weight structures of composite materials and advances in manufacturing processes have increased the use of composite materials in the aerospace and wind energy industries as a primary load carrying structures in complex shapes. However, use of composite materials in complex geometries such as L-shaped laminates creates weakness at the radius which causes delamination. Carbon nanotubes (CNTs) is preferred as a toughening materials in composite matrices due to their high mechanical properties and aspect ratios. However, effect of CNTs on curved beam strength (CBS) is not investigated in literature comprehensively. The objective of this study is to investigate the effect of CNT on Mode I and Mode II fracture toughness and CBS. L-shaped beams are fabric carbon/epoxy composite laminates manufactured by hand layup technique. Curved beam composite laminates were subjected to four point bending loading according to ASTM D6415/D6415M-06a. Double cantilever beam (DCB) tests and end notch flexure (ENF) tests were conducted to determine mode-I and mode-II fracture toughness, respectively. Preliminary results show that 3% CNT addition to the resin increased the mode-I fracture toughness by %25 and mode-II fracture toughness by %10 compared to base laminates. In contrast, no effect on curved beam strength was found.

Interlaminar fracture toughness of CFRP laminates with silk fibers interleave

Interlaminar fracture toughness of CFRP laminates with silk fibers interleave was evaluated in this paper. Silk fibers were obtained from silkworm cocoon. Long silk fibers were wound around a bobbin and cut into specimen size. Resin films were bonded on both sides of a sheet of silk fibers. Silk fibers with resin films were put between [012] and [012] and cured by following the curing process. Evaluation of mode I and mode II interlaminar fracture toughness was accomplished by DCB and ENF test, respectively. Mode I interlaminar fracture toughness of CFRP laminates with silk fibers interleave was 59% higher than that of CFRP. Mode II interlaminar fracture toughness of CFRP laminates with silk fibers interleave was 44% higher than that of CFRP. It seems that CFRP laminates with silk fibers interleave will be useful to structures which need high interlaminar fracture toughness.

종류가 다른 부직포가 삽입된 하이브리드 복합재료의 모드 II 층간파괴인성

ABSTRACT: The mode II interlaminar fracture toughness was evaluated for CFRP laminates with different types of non-woven tissues and the source of increased mode II interlaminar fracture toughness was examined by SEM analysis in thispaper. The interlaminar fracture toughness in mode II is obtained by an end notched flexure test. The experiment isperformed using three types of non-woven tissues: 8 g/m 2 of carbon tissue, 10 g/mof glass tissue, and 8 g/mof polyestertissue. On the basis of the specimen with no non-woven tissue, interlaminar fracture toughness on mode II at specimensinserted with non-woven carbon and glass tissues and polyester tissues increases as much as 166.5% and 137.1% and157.4% respectively. The results show that mode II interlaminar fracture toughness of CFRP laminates inserted with non-woven tissues increased due to the fiber bridging, fiber breakage, and hackle etc. by SEM analysis.초록 : 본 연구에서는 CFRP 적층판에 다양한 종류의 부직포를 삽입하여 모드 II 층간파괴인성을 평가하고, 파단면의 SEM 분석을 통해 층간파괴인성의 증가 원인을 파악하였다. 모드 II 층간파괴인성값(J/m

Reinforcement effects of MWCNT and VGCF in bulk composites and interlayer of CFRP laminates

The reinforcement effects of two nanofillers, i.e., multi-walled carbon nanotube (MWCNT) and vapor grown carbon fiber (VGCF), which are used at the interface of conventional CFRP laminates, and in epoxy bulk composites, have been investigated. When using the two nanofillers at the interface between two conventional CFRP sublaminates, the Mode-I interlaminar tensile strength and fracture toughness of CFRP laminates are improved significantly. The performance of VGCF is better than that of MWCNT in this case. For epoxy bulk composites, the two nanofillers play a similar role of good reinforcement in Young’s modulus and tensile strength. However, the Mode-I fracture toughness of epoxy/MWCNT is much better than that of epoxy/VGCF.

Fracture toughness improvement of CFRP laminates by dispersion of cup-stacked carbon nanotubes

Several techniques are introduced to enhance the interlaminar fracture toughness of CFRP laminates using cup-stacked carbon nanotubes (CSCNTs). Prepared CSCNT-dispersed CFRP laminates are subject to Double Cantilever Beam (DCB) and End Notched Flexure (ENF) tests in order to obtain mode-I and mode-II interlaminar fracture toughness. The measured fracture toughnesses are compared to that of CFRP laminates without CSCNT to evaluate the effectiveness of CSCNT dispersion for the improvement of fracture toughness. All CSCNT-dispersed CFRP laminates exhibit higher fracture toughness, and specifically, CSCNT-dispersed CFRP laminates with thin epoxy interlayers containing short CSCNTs have three times higher fracture toughness than CFRP laminates without CSCNT. SEM observation of fracture surfaces is also conducted to investigate the mechanisms of fracture toughness improvement. Crack deflection mechanism is recognized in the CSCNT-dispersed CFRP laminates, which is considered to contribute the enhancement of interlaminar fracture toughness.

Effect of Residual Stress on Interlaminar Fracture Toughness of CFRP Laminates

In the present study, an effect of residual stress in CFRP laminates for the interlaminar fracture toughness was investigated in detail. The boundary element method based on the Laplace transform were employed to calculate the residual stress and interlaminar fracture toughness of the CFRP laminates. The relaxation moduli of the CFRP laminates were estimated by unidirectional compression creep test experimentally. Using CFRP specimens of orthogonal stacking sequence [0°/90°/0°], double cantilever beam (DCB) test for opening mode crack and end notch flexure (ENF) test for shear mode crack were introduced to obtain the actual fracture toughness of CFRP laminates, where the effect of the residual stress in the cooling sequence of the making process was taken into account. From the experimental results and numerical demonstrations by BEM, it was shown that there is a possibility of underestimation of the interlaminar fracture toughness if it is calculated by elastostatic analysis neglecting the residual stress. On the other hand, there is a possibility of overestimation of the toughness when thermoelastic analysis is applied without thermo-viscoelastic properties.

Mode I and mode II interlaminar fracture toughness of CFRP laminates toughened by carbon nanofiber interlayer

Interlaminar fracture toughness for mode I and II deformation were investigated for carbon fiber (CF)/epoxy laminates toughened by a carbon nanofiber/epoxy interlayer. Vapor grown carbon fiber (VGCF) and vapor grown carbon nanofiber (VGNF) were chosen as the reinforcement for the interlayer. To illustrate the effect of the interlayer on the fracture toughness of the laminates, several types of carbon fiber reinforced plastics/carbon nanofiber (CFRP/CNF) hybrid laminates were fabricated. Each laminate was composed of unidirectional carbon/epoxy prepregs with carbon nanofiber varying the interlayer thickness. Mode I interlaminar fracture toughness was evaluated by a standard double cantilever beam (DCB) test. Mode II interlaminar fracture toughness was evaluated by an end notched flexure (ENF) test using a three point bending test. The experimental results of the DCB test confirms that the mode I interlaminar fracture toughness for hybrid laminates is about 50% greater than the base CFRP laminates. Furthermore, the results of the mode II fracture toughness test confirms that the interlaminar fracture toughness for hybrid laminates is 2–3 times greater than base CFRP laminates. In addition, the results revealed the recommended range of CNF interlayer thickness is between 100 and 150 μm (approximately 20 g/m 2 carbon nanofiber area density). The difference in the effect of the interlayer fracture properties under mode I and II deformation was discussed on the basis of fractographic observations derived from scanning electric microscope.

A method for predicting the fracture toughness of CFRP laminates failing by fibre microbuckling

Abstract Cohesive zone models have had notable success in the prediction of damage from notches in engineering materials loaded in tension. They have also been used to determine the growth of fibre microbuckling from a hole in a composite laminate under compression, (Soutis C, Fleck NA, Smith PA. Failure prediction technique for compression loaded carbon fibre/epoxy laminate with an open hole. J Compos Mater, 1991;25(11):1476–1498). The usual strategy is to replace the inelastic deformation associated with plasticity or microbuckling with a line-crack and to assume some form of stress-displacement bridging law across the crack faces. For instance, in the Dugdale analysis of plastic deformation in metals from the root of a notch (Dugdale DS. Yielding of steel sheets containing slits, J Mech Phys Solids, 1960;8:100–104), it is assumed that the bridging normal traction across the crack faces equals the tensile yield strength of the solid. The material response elsewhere in the cracked structure is assumed to be linear elastic. In this paper, a new method is presented for the calculation of the fracture energy G c associated with fibre microbuckling, a parameter required in the Soutis et al. linear softening cohesive zone model for the prediction of the open hole compression strength. Theoretical results are found to be in good agreement with experimental data for several carbon fibre–epoxy laminates.

Analysis of stress and displacement fields in interlaminar-toughened composite laminates with transverse cracks

In recent years, to enhance the interlaminar fracture toughness of CFRP laminates, interlaminar-toughened laminates have been developed in which resin rich layers are placed in interlaminar regions. In the present study, stress and displacement fields in interlaminar-toughened cross-ply laminates with transverse cracks are analyzed. The analysis is based on a two-dimensional model which assumes that generalized plane strain conditions prevail. Account is taken of thermal residual stresses arising from a mismatch in thermal expansion coefficients of the 0° ply, interlaminar resin and 90° ply. The analytical results are shown for the laminates with interlaminar resin layers of various thicknesses. The analysis will be a basis for the optimal design of laminates with interlaminar resin layers.

Transverse cracking in CFRP cross-ply laminates with interlaminar resin layers

In recent years, interlaminar-toughened laminates have been developed in which resin rich layers are placed in interlaminar regions in order to enhance the interlaminar fracture toughness of CFRP laminates. In the present study, a predictive method is developed for transverse cracking in CFRP cross-ply laminates with interlaminar resin layers at 0/90° interfaces under static tensile loading. The analysis is based on a two-dimensional approximate elastic analysis considering the interlaminar resin layers and thermal residual stresses. To predict transverse cracking, both energy and stress criteria are used. The change in thermoelastic properties of a laminate due to transverse cracking is also predicted. To investigate the validity of the analysis, loading-unloading tests are performed to obtain Young's modulus reduction as a function of the transverse crack density. The predictions of transverse crack density as a function of the laminate strain are compared with our previous experimental results. A good agreement is obtained which implies the validity of the present analysis.

Transverse Cracking in CFRP Laminates with Interlaminar-Resin Layers.

In recent years, interlaminar-toughened laminates are developed in which resin rich layers are placed in interlaminar regions in order to enhance the interlaminar fracture toughness of CFRP laminates. Tensile tests are conducted on CFRP cross-ply laminates with interlaminar resion layer at 0/90 interfaces. Transverse crack density is measured as a function of the laminate strain. To investigate temperature effect. tests are conducted at room temperature and 80°C. Laminate configurations are cross-ply (0/A/90m/A/0) where A denotes interlaminar resin layer and m=4.8 and 12. The experimental results are compared with the theoretical prediction based on the two-dimensional analysis considering the interlaminar resin layers and thermal residual stresses. The validity of the energy criterion and strength criterion is discussed.

Analysis of Stress and Displacement Fields in Interlaminar-Toughened Composite Laminates with Transverse Cracks.

In recent years, to enhance the interlaminar fracture toughness of CFRP laminates, interlaminar toughened laminates have been developed with resin-rich layers in the interlaminar regions. In the present study, stress and displacement fields in interlaminar-toughened cross-ply laminates with transverse cracks are analyzed. The analysis is based on a two-dimensional model which assumes that generalized plane strain conditions prevail. Thermal residual stresses arising from a mismatch in thermal expansion coefficients of the 0°, interlaminar resin and 90°plies are considered. The analytical results are shown for the laminates with interlaminar resin layers of various thicknesses. The analysis will provide a basis for the optimal design of laminates with interlaminar resin layers.

Young's Modulus Reduction due to Transverse Cracking in Interlaminar-Toughened Composite Laminates.

In recent years, interlaminar-toughened laminates are developed in which resin rich layers are placed in interlaminar regions in order to enhance the interlaminar fracture toughness of CFRP laminates. In this paper, Young's modulus reduction due to transverse cracking in interlaminar-toughened CFRP cross-ply laminates are measured as a function of transverse crack density. Loading unloading tests are conducted at room temperature and 80°C to investigate temperature effect. Laminate configurations are cross-ply (0/A/90m/A/0) where A denotes interlaminar resin layer and m=4.8 and 12. The experimental results are compared with the theoretical prediction based on the two-dimensional analysis considering the interlaminar resin layers and thermal residual stresses.

高分子系複合材料 くさび挿入試験によるＣＦＲＰ積層材のモードＩ層間破壊じん性評価

A new estimating method for mode I interlaminar fracture toughness of CFRP laminates was proposed with the aim of applying to dynamic fracture test. In this method, a wedge indentor was used to cause mode I interlaminar fracture in a precracked coupon specimen. That is, compressive load, which is convenient to dynamic test, can be used in this method, while tensile load, which is not appropriate to dynamic test, is necessary for the conventional double cantilever beam test. Finite element analyses and quasi-static experiments were carried out to validate an estimating formula for the mode I energy release rate, which is based on the beam theory and the compliance method. As the result, this method is found to be able to estimate the mode I interlaminar fracture toughness of CFRP laminates and to obtain the same stress field as the one formed in the double cantilever beam specimen. But in this method one has to measure accurately the crack length at the fracture initiation, which is difficult under high rate loading. Three types of CFRP laminates were tested in order to investigate the effect of the toughness of matrix resin. They are: T300/2500 (Toray) which has standard epoxy matrix resin, IM600/133 (Q-C133, Toho rayon) which has toughened epoxy matrix resin, and HTA/PEEK (Toho rayon) which has thermoplastic matrix resin of high fracture toughness. The experimental results show that the toughness of the matrix resin scarcely affects the estimation of the mode I interlaminar fracture toughness and that the fracture toughness estimated by the present method is comparable to that estimated by the double cantilever beam test.

繊維配向角がＣＦＲＰ積層板のモードＩおよびモードＩＩ層間破壊靭性に及ぼす影響

The objective of this study was to investigate the effect of fiber orientation on Mode I and Mode II interlaminar fracture toughness of CFRP laminates by conducting DCB (Double Cantilever Beam) tests and ENF (End Notched Flexure) tests. In Mode I loading, Mode I interlaminar fracture toughness at initiation, GIC, became higher as the fiber orientation inclined to the crack propagating direction. Mode I interlaminar fracture toughness during propagation, GIR, were almost constant macroscopically in two cases of the delamination at [0/0] interlamina of unidirectional specimen and the [(0/90)/(0/90)] interlamina of plain weave specimen. The delamination at [0/0] interlamina showed a stable fracture behavior. However, the delamination at [(0/90)/(0/90)] interlamina showed a cross-linked stable-unstable fracture behavior. Contrary to it, GIR increased immediately as the crack propagated and as the fiber orientation inclined to the crack propagating direction. In Mode II loading, Mode II interlaminar fracture toughness at initiation, GIIC, became lower, on the contrary to the case of Mode I, as the fiber orientation inclined to the crack propagating direction. Mode II interlaminar fracture toughness during propagation, GIIR, increased immediately as the crack propagated, nothing to do with the fiber orientation, and as the fiber orientation inclined to the crack propagating direction. The fracture surface observation by SEM was also added.