Mechanical and open hole tensile properties of self‐reinforced PET composites with recycled PET fiber reinforcement

The tensile strength of notched composites is an important factor for composite structural design. However, no literature is available on the notch sensitivity of self‐reinforced polymer composites. In this study, self‐reinforced recycled poly (ethylene terephthalate) (srrPET) composites were produced by film stacking from fabrics composed of double covered uncommingled yarns (DCUY). Composite specimens were subjected to uniaxial tensile, flexural, and Izod impact tests and the related results compared with earlier ones achieved on srPET composites reinforced with nonrecycled technical PET fibers. Effects of open circular holes on the tensile strength of srrPETs were studied at various width‐to‐hole diameter (W/D) ratios of the specimens. In the open hole tensile (OHT) measurements bilinear (yielding followed by post‐yield hardening) stress–strain curves were recorded. The srrPET composites had extremely high yield strength retention (up to 142%) and high breaking strength retention (up to 81%) due to the superior ductile nature of the srrPETs, which induces plastic yielding near the hole thereby reducing the stress concentration effect. The results proved that srrPET composites are tough, ductile notch‐insensitive materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43682.     

国产碳纤维CCF300增强QY8911双马树脂含孔复合材料拉压疲劳试验研究

碳纤维树脂基复合材料（CFRP）层合板的疲劳性能决定了结构的安全性和可靠性。其寿命预测的研究具有重要的工程意义。依据碳纤维复合材料拉压疲劳试验标准,对含孔国产碳纤维CCF300／QY8911复合材料进行了5个不同应力水平下拉压疲劳试验,分析了疲劳试样断口,表征了中央含孔国产碳纤维CCF300／QY8911复合材料在疲劳载荷作用下的破坏过程,获得含孔复合材料层合板的条件疲劳极限,在此基础上,建立了复合材料的S-N曲线。利用该曲线可对中央含孔复合材料进行疲劳寿命预测。10^6下的条件疲劳极限为平均应力的48％（即150．3MPa）。     

Comparison of models for notched strength of carbon fibre reinforced polymer laminates

Abstract

A modified point stress criterion has been used for evaluating the tensile fracture strength of AS-4 carbon–984A1 epoxy [0/90]_4S and [0/±45/90]_2S composite laminates with various hole diameters and specimen widths. The results correlate well with the existing test results, and with those predicted from an effective crack growth model.     

Stress analyses of composite tee joints at elevated temperature

Thermal–structural coupling nonlinear finite element analyses are conducted in this paper to determine three-dimensional stresses of a composite tee joint, which is formed when a right angled plate is adhesively bonded to a base plate at elevated temperature. The von-Mises stresses of the adhesive layer of the tee joint with three different laminate stacking sequences viz. unidirectional [0]₈, cross-ply [(0/90)_s]₂, and angle-ply [(+45/?45)_s]₂ laminates have been evaluated when the tee joint is subjected to an out-of-plane loading through the right angled plate in addition to an elevated temperature applied at the undersurface of the base plate. The effects of laminate stacking sequence and temperature on von-Mises stresses have been investigated in this paper. The effects of the coefficient of thermal expansion and thermal conduction of the adhesive layer on von-Mises stresses have also been studied. Conclusions about the stresses of the composite tee joint with different stacking sequence, different coefficient of thermal expansion, and different thermal conduction of the adhesive layer are drawn.     

Bearing strength of pin‐connected polymer composites subjected to dynamic loading

In this study, static load bearing strength of pin‐connected carbon fiber‐reinforced polyphenylenesulphide (PPS) composites that have [(0°/90°)]_3s stacking sequence was investigated. Firstly, the samples were loaded dynamically, and then the same samples were loaded statically. The results obtained from this sequential experiment were compared with the results obtained from samples that were loaded only statically. In addition, the fatigue life and failure mechanisms were investigated with respect to the selection of the geometrical parameters. Dynamic and static loading experiments were performed according to the ASTM STP 749 and ASTM D953 standards, respectively. To obtain optimum load bearing values, the ratio of distance between the edge and hole center to hole diameter (E/D) and ratio of sample width to hole diameter (W/D) has been systematically changed. According to the experimental results, maximum load bearing values have been obtained when E/D ratio was equal to 2. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Effect of compressive loading speed and stacking sequence on mechanical characteristics of satin weave E‐glass/epoxy composites

This article experimentally investigated the in‐plane loading speed dependent mechanical properties and failure modes of satin weave E‐glass/epoxy composite laminates [45/−45/0/90]_ns. Two types of E‐glass fabric/epoxy pre‐impregnated tapes were used to manufacture the composite laminates specimens. The low strain rate tests were conducted with an INSTRON™ testing machine, and the high strain rate tests done using a pulse shape modified compressive Split Hopkinson Pressure Bar apparatus. From the experimental result, it was concluded that under different strain rate loading, compressive strength, modulus, and strain at peak stress were rate sensitive. Optical and microscopic photos of the specimens were taken to determine operative failure modes. Within the studied strain rate regimes, the failure mode changed from splitting followed by fiber kink buckling to predominantly delamination and shear fracture as strain rate increases from quasi‐static to high strain rates. Compressive properties and failure modes were severely affected by strain rate, stacking sequence, and fabric material. POLYM. COMPOS. 2012. © 2012 Society of Plastics Engineers     

Polyester composites of short pineapple fiber and glass fiber: Tensile and impact properties

The tensile and impact performance of intimately mixed (IM) hybrid composites based on glass fiber (GF) and pineapple leaf fiber (PALF) was investigated. The composite was fabricated at constant volume fraction of fiber 0.3 V_f (fiber 0.3 and matrix 0.7). Keeping the volume fraction of matrix a constant (0.7 V_f), we have varied the PALF/GF ratio from 0 to 1. Incorporation of 0.1 volume fraction of GF increases the tensile strength of the hybrid composite by about 28%. The tensile strength showed a further increase when the volume fraction is changed to 0.7 and 0.9 V_f of GF. Intimately mixed hybrid composites exhibited higher impact strength than the individual fiber composites; the composite of PALF/GF ratio 70:30 showed maximum impact strength of 1203 J/m. A positive hybrid effect is observed for impact properties. Scanning electron micrographs of the fractured surfaces were examined to understand the fiber‐matrix adhesion. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Progressive failure analysis of carbon-fibre/epoxy composites laminates to study the effect of stitch densities under in-plane tensile loading

Through thickness reinforced stitched laminates with different stitch densities (0.11 and 0.028?mm^?2) were studied in order to analyse effects on laminate behaviour, under in-plane tensile loading based on continuum mechanics. Multi-layered stitched laminates with the stacking sequence [+45/90/?45/0₂/+45/90₂/?45/0]_s were modelled on a lamina-wise basis to analyse the macroscopic damage and local stress–strain constitutive behaviour. Interfaces between lamina and stitch yarns were assumed to be perfectly glued and were modelled by the contact capability. Discretisation procedures using the principle of virtual work were applied in addition to discretisation of the contact traction. Progressive failure analysis with Puck’s failure criteria was conducted to characterise the failure behaviour of the laminate. This analysis showed that reinforcement density is one of the key factors affecting strength, stiffness and crack propagation in composite laminates. By suppressing the damage initiation, densely stitched laminates showed 15.2% higher in-plane stiffness than moderately stitched laminates. The results obtained by the finite element technique are consistent with the experimental results.     

Torque Transmission Capabilities of Bonded Polygonal Lap Joints for Carbon Fiber Epoxy Composites

Although carbon fiber epoxy composite materials have excellent properties for structures, the joint in composite materials often reduces the efficiency of the composite structure because the joint is often the weakest area in the composite structure.

In this paper, the effects of the adhesive thickness and the adherend surface roughness on the static and fatigue strengths of adhesively-bonded tubular polygonal lap joints have been investigated by experimental methods. The dependencies of the static and fatigue strengths on the stacking sequences of the composite adherends were observed.

From the experimental investigations, it was found that the fatigue strength of the circular adhesively-bounded joints was quite dependent on the surface roughness of the adherends and that polygonal adhesively-bonded joints had better fatigue strength characteristics than circular adhesively-bonded joints.     

Open hole flexural and izod impact strength of unidirectional flax yarn reinforced polypropylene composites as a function of laminate lay‐up

An open hole flexural strength and impact energy of flax yarn‐reinforced polypropylene (PP) composites were studied in this work. Highest flexural strength and strength retention were observed for axial (0₆) and cross‐ply (0/90/0)_s laminates, respectively, while also examining the influence of laminate lay‐up and open hole size on flexural strength. It was found that maleic anhydride‐grafted polypropylene (MAPP)‐treated composite laminates achieved marginal improvement on flexural strength for all kinds of laminate lay‐up. Off‐axial laminates (±45₆) showed a good strength retention for open hole laminates after MAPP treatment. The fractography study confirmed microbuckling and matrix crack propagation over the compressive and tensile side of the laminate, respectively. Furthermore, severe surface damage was detected over the tensile side of 8‐mm hole size laminates. Impact test of the flax/PP laminates showed slight improvement by MAPP treatment. High‐ and low‐impact energy was experienced for axial and off‐axial laminates. The damaged impact sample shows evidence of fiber pull‐out for untreated flax yarn reinforced laminates. POLYM. COMPOS., 34:1912–1920, 2013. © 2013 Society of Plastics Engineers     

Temperature and loading speed sensitivity of glass/carbon inter-ply hybrid polymer composites on tensile loading

This study is focused on the evaluation of the tensile performance of glass/carbon inter-ply hybrid fiber-reinforced polymer composites at different combinations of temperatures and loading speeds. With an increase in the number of carbon/epoxy (CE) ply in glass/epoxy (GE) composites, some of the tensile properties as tensile modulus, strain at failure, and difference of strain at failure of different fibers are enhanced. Further, the change in the stacking sequence of the CE ply at a particular hybrid ratio alters the tensile properties as well as the nature of failure. Placing a CE ply in place of GE ply at the center in the GE composite resulted in hybrid composite (G₂C₁G₂) that imparts pseudo-ductility as well as hybrid effect in the composite. On the other hand, replacing a GE ply with CE at one end (C₁G₄) and both ends (C₁G₃C₁) imparted improved strain at failure and positive hybrid effect in the composites. The tensile modulus of G₂C₁G₂ outstrips the modulus of CE and GE by 12.05% and 65.95% at a loading speed of 0.1 mm/min and a temperature of 110°C. Fractography analysis of neat as well as hybrid composites was done to analyze the fracture mechanism.     

Surface treatment of CFRP composites by Ar+ irradiation to improve bonding strength between aluminum and CFRP composites

The effect of surface treatment of carbon fiber reinforced plastic (CFRP) composites on the T-peel strength and the shear strength between CFRP and aluminum panels was studied. The surface of the composite panel was treated with Ar⁺ irradiation under oxygen environment. The optimal Ar⁺ ion dose was determined by measuring the changes of contact angle and surface energy as a function of ion dose. T-peel tests and SLS tests were performed using irradiated CFRP/aluminum specimens and unirradiated CFRP/aluminum specimens to determine the treatment effect by Ar⁺ irradiation under oxygen environment on the T-peel strength and shear strength of CFRP/aluminum composites. The results showed that contact angle on the surface of the composite panel was reduced from ∼80° to ∼8° and the surface energy increased from 31 ergs/cm² to 72.4 ergs/cm² with an ion dose of 10¹⁷ ions/cm². T-peel strength and shear strength are significantly affected by the surface treatment of composite panel. T-peel strength and shear strength improved 650% and 56%, respectively, when the treatment was made with an ion dose of 10¹⁶ ions/cm². SEM examination showed that the improvement of bonding strength was attributed to the uniform spread and fracture of epoxy adhesive.     

Structure,morphology, and properties of HNBR filled with N550, SiO2, ZDMA,and two of three kinds of fillers

The vulcanization properties, mechanical properties of hydrogenated nitrile rubber (HNBR) filled with carbon black (N550), zinc dimethacrylate (ZDMA), SiO₂ independently and two of three kinds of fillers together were investigated, respectively. The filler‐dispersion was characterized by the transmission electron microscopy (TEM) and dynamic mechanical properties. The results showed that HNBR composite filled with SiO₂ or ZDMA displayed high tensile strength, elongation at break and compression set. The HNBR composite filled with N550 displayed low compression set, tensile strength and elongation at break. The dispersion of SiO₂ in HNBR compound was better than that in HNBR vulcanizates because of SiO₂ particles self‐aggregation in vulcanizing processing. ZDMA particles with micron rod‐like and silky shape in HNBR compounds changed into near‐spherical poly‐ZDMA particles with nano size in HNBR vulcanizates by in situ polymerization reaction. The N550 particles morphology exhibited no much change between HNBR compounds and vulcanizates. N550/ZDMA have the most effective reinforcement to HNBR and the appropriate amount of ZDMA is about 25% of total filler amount by weights. The theory prediction for Payne effect (dispersion of the filler) shown by the dynamic properties is identical with actual state observed by TEM. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of PANI–PVA composite film with good conductivity and strong mechanical property

The polyaniline (PANI)–polyvinyl alcohol (PVA) conductive composite films [doped with hydrochloride (HCl), dodecylbenzene sulphonic acid and amino sulphonic acid (NH₂SO₃H) aqueous solution] were synthesised by ‘in situ’ polymerisation, and their conductivities were compared. Among these composite films, HCl–PANI–PVA composite film possessed the highest conductivity that reached 1360?S·m^??1 [w_(PVA)?=?40%]. Meanwhile, the effects of PVA content, HCl concentration, oxidant ammonium persulphate (APS) dosage, reaction time and film drying temperature on tensile strength of the HCl–PANI–PVA composite films were studied. The tensile strength of the film was improved greatly due to effective mixture of PANI and PVA. When the PVA content was 40%, C_(HCl)?=?1.0?mol·L^??1, reaction time was 4.0?h, n_(APS)/n_(aniline)?=?1.0 and film drying temperature was 80°C, and the tensile strength of the HCl–PANI–PVA composite film reached the maximum of 60.8?MPa. At the same time, the structure of composite materials was characterised and analysed through ultraviolet spectrum and SEM.     

Investigation of debonding propagation in aluminum/composite joints under fatigue loading

In this paper, Fracture Mechanics is used to predict debonding propagation in adhesive joint between aluminum and composite plates. Three types of loadings (λ = 0, λ = 0.5, and λ = 1 when λ is the ratio of lateral to in-plane loading) and two types of glass–epoxy composite sequences: [0/90]_2s and [0/45/?45/90]_s are considered for the composite plate and their results are compared. It was seen that generally the cases with stacking sequence of [0/45/?45/90]_s have much shorter lives than cases with [0/90]_2s. It was also seen that in cases with λ = 0, the ends of the debonding front propagates forward more than its middle, while in cases with λ = 0.5 or λ = 1 it is vice versa. Moreover, regardless of value of λ, the difference between the debonding propagations of the ends and the middle of the debonding front is very close in cases λ = 0.5 and λ = 1. Another main conclusion was that the non-dimensionalized debonding front profile is almost independent of sequence type or the applied load value.     

Preparation and characterization of polyether‐based polyurethane dolomite composite

A polyether polyol‐based two‐component polyurethane composite was prepared by a reaction of polypropylene glycol (PPG) and diethylene glycol (DEG) used as a crosslinker. The final reaction for the preparation of composite is carried out with processed polyether polyol and diphenylmethane 4,4′‐diisocyanate (MDI). The physicochemical properties of processed polyether polyol have been measured, such as viscosity, moisture content, and hydroxyl value. The composite has been formed with loading of inorganic filler dolomite [MgCa(CO₃)₂] with different filler ratios. It shows good adhesive strength and mechanical properties. Composite samples have also been studied for the effects of acids and bases, swelling in solvents, physical and mechanical properties such as compression strength, shore hardness A and D, tensile strength, and elongation. Some electrical properties have also been studied, viz. thermal conductivity, volume resistivity, and dielectric strength. A comparison of prepared polyether‐based polyurethane composite with some conventional polymeric materials suggests their suitability for various applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2337–2342, 2007     

基于应力和变形值最小的复合材料含孔板孔形参数有限元优化

本文基于对复合材料孔板主承力接触区的有限元强度分析结果,利用APDL参数化有限元分析技术,以孔板第一主应力S1和X方向上的变形UX的最大值作为目标函数,对孔形参数进行优化。设计出基于应力和变形最小的开口形状,并得出了孔形参数与应力、变形之间的相互关系。     

A study of the mechanical properties of randomly oriented short banana and sisal hybrid fiber reinforced polyester composites

The mechanical performance of short randomly oriented banana and sisal hybrid fiber reinforced polyester composites was investigated with reference to the relative volume fraction of the two fibers at a constant total fiber loading of 0.40 volume fraction (V_f), keeping banana as the skin material and sisal as the core material. A positive hybrid effect is observed in the flexural strength and flexural modulus of the hybrid composites. The tensile strength of the composites showed a positive hybrid effect when the relative volume fraction of the two fibers was varied, and maximum tensile strength was found to be in the hybrid composite having a ratio of banana and sisal 4 : 1. The impact strength of the composites was increased with increasing volume fraction of sisal. However, a negative hybrid effect is observed when the impact strength of the composites is considered. Keeping the relative volume fraction of the two fibers constant, that is, banana : sisal = 0.32 : 0.08 (i.e., 4 : 1), the fiber loading was optimized and different layering patterns were investigated. The impact strength of the composites was increased with fiber loading. Tensile and flexural properties were found to be better at 0.40 V_f. In the case of different layering patterns, the highest flexural strength was observed for the bilayer composites. Compared to other composites, the tensile properties were slightly higher for the composite having banana as the skin material and sisal as the core material. Scanning electron micrographs of the tensile and impact fracture surfaces of the hybrid composites having volume fraction 0.20 and 0.40 V_f were studied. The experimental tensile strength and tensile modulus of hybrid composites were compared with those of theoretical predictions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1699–1709, 2005     

Effects of interface bonding properties on cyclic tensile behavior of unidirectional C/Si3N4 and SiC/Si3N4 composites

In this paper, the effect of fiber/matrix interface bonding properties on the cyclic loading/unloading tensile stress?strain hysteresis loops of 2 different ceramic‐matrix composites (CMCs), ie, C/Si₃N₄ and SiC/Si₃N₄, has been investigated using micromechanical approach. The relationships between the damage mechanisms (ie, matrix multicracking saturation, fiber/matrix interface debonding and fibers failure), hysteresis dissipated energy and internal frictional damage parameter have been established. The damage evolution processes under cyclic loading/unloading tensile of C/Si₃N₄ and SiC/Si₃N₄ composites corresponding to different fiber/matrix interface bonding properties have been analyzed through damage models and interface frictional damage parameter. For the C/Si₃N₄ composite with the weakest fiber/matrix interface bonding, the composite possesses the lowest tensile strength and the highest failure strain; the hysteresis dissipated energy increases at low peak stress, and the stress?strain hysteresis loops correspond to the interface partially and completely debonding. However, for the SiC/Si₃N₄ composite with weak interface bonding, the composite possesses the highest tensile strength and intermediate failure strain; and the hysteresis dissipated energy increases faster and approaches to a higher value than that of composite with the strong interface bonding.     

Experimental and numerical investigations of adhesively bonded CFRP single-lap joints subjected to tensile loads

In this study, both experimental tests and numerical simulation are implemented to investigate the tensile performance of adhesively bonded CFRP single-lap joints (SLJs). The study considers 7 different overlap lengths, 5 adherend widths and 3 stacking sequences of the joints. Three-dimensional (3D) finite element (FE) models are established to simulate the tensile behavior of SLJs. The failure loads and failure modes of SLJs are investigated systematically by means of FE models and they are in good agreement with those of experiments, proving the accuracy of finite element method (FEM). It is found that increasing the adherend width can improve the load-carrying capacity of the joint better than increasing the overlap length does. Moreover, choosing 0° ply as the first ply is also beneficial for upgrading joint's strength. With respect to failure modes, cohesive failure in adhesive and delamination in adherend take dominant, while matrix cracking and fiber fracture only play a small part. With overlap length increasing or adherend width decreasing, cohesive failure takes up a smaller and smaller proportion of whole failure area, but the opposite is true for delamination. SLJs bonded with [0/45/-45/90]_3S adherends are prone to cohesive failure, and [90/-45/45/0]_3S adherends are easy to appear delamination. Both shear and peel stress along the bondline indicate symmetrical and non-uniform distributions with great stress gradient near the overlap ends. As the load increases, the high stress zone shifts from the end to the middle of the bondline, corresponding to the damage initiation and propagation in the adhesive layer.