Fatigue behavior of filament‐wound glass fiber reinforced epoxy composite tubes under tension/torsion biaxial loading

A study of filament‐wound glass fiber/epoxy composite tubes under biaxial fatigue loading is presented. The focus is placed on fatigue lives of tubular specimens under tension/torsion biaxial loading at low cycle up to 100,000 cycles. Filament‐wound glass‐fiber/epoxy tubular specimens with three different lay‐up configurations, namely [±35°]_n, [±55°]_n, and [±70°]_n lay‐ups, are subjected to in‐phase proportional biaxial cyclic loading conditions. The effects of winding angle and biaxiality ratio on the multiaxial fatigue performance of composites are discussed. Specimens are also tested under two cyclic stress ratio: R = 0 and R = −1. The experimental results reveal that both tensile and compressive loading have an influence on the multiaxial fatigue strength, especially for [±35°]_n specimens. A damage model proposed in the literature is applied to predict multiaxial fatigue life of filament‐wound composites and the predictions are compared with the experimental results. It is shown that the model is unsuitable for describing the multiaxial fatigue life under different cyclic stress ratios. POLYM. COMPOS. 28:116–123, 2007. © 2007 Society of Plastics Engineers     

A ply-level electrical resistance approach to monitor crack evolution in a laminate SiC/SiC composites

In the aim of providing a reliable technique to monitor the development of damage in 0°/90° melt-infiltrated SiC-fiber reinforced prepreg laminate ceramic-matrix composites, it was hypothesized that the electrical resistivities of different layers of this material were significantly different due to their free Si content and morphology. Three distinct layers: a 0° fiber ply, a 90° fiber ply and a matrix only ply, were distinguished in the composite architecture. Free silicon is the most conductive phase in this composite system; however, the Si content and morphology were different in each of the three types of plies. Unidirectional and [0°/90°]_2s specimens enabled quantification of ply-level resistivities. An electric circuit model was constructed; it consists of parallel resistors where each resistor represents a ply in the composite system. This ply-level electrical model was validated using composites of different vintages which contained different silicon contents. A room temperature stepped fatigue test was conducted and the ply level circuit model was used to discern crack morphology with the support of acoustic emission and digital image correlation.     

Compression after impact (CAI) strength of concrete cylinders reinforced by non‐adhesive filament wound composites

Concrete cylinders reinforced by filament wound composites were fabricated, and the compressive strength of the composite/concrete cylinders was tested after low‐energy impact. In this study, a glass fiber woven cloth wrapping method and a filament winding technique were adopted to wrap the concrete cylinder. In order to investigate the influence of composite/concrete interfacial bonding on the compression after impact (CAI) strength, aluminum foil was introduced into the composite/concrete interface; thus, the compressive behavior of the composite/concrete system with or without inserting the aluminum foil was compared. The effects of aluminum foil in the curing process were also revealed. Based upon the results of this study, the placement of aluminum foil can significantly enhance the compressive strength of the composite/concrete cylinder. The CAI strength depicts that the winding angle used in the filament winding process can significantly influence the reinforcing effects. Among the tested cylinders, the FWIC (defined in the text) [90₂/±60/90₂] cylinder shows the highest CAI strength—129.4 MPa—which is 4.5 times higher than the impacted concrete cylinder and 4.1 times higher than the pure concrete cylinder. Fracture mode was also investigated on the cylinder reinforced by the composites wound with different winding angles. The placement of aluminum foil reduces shear stress transfer across the composite/concrete interface, which affects not only the impact response but also the compressive strength.     

Mechanical characterization in laminated composite for cryogenic application

Damage in cryogenic composite fuel tanks induced during manufacturing and advanced by thermomechanical cycling can accelerate leakage of the propellant. Whether the leakage exceeds tolerable levels depends on many factors, including pressure gradients, microcrack density, other damage such as delamination, connectivity of the cracks, residual stresses from manufacture, service‐induced stresses from thermal and mechanical loads, and composite lay‐up. This article is concerned with the creation and the detection of damage in cryogenic composites due to thermomechanical loading. The first part deals with cryocycling (cycling between two temperatures) test procedures, that were developed to understand the damage produced in cryogenic composite laminates under thermomechanical loading. An apparatus was developed to thermomechanically cycle coupon test specimens under different thermomechanical loadings. IM7/977‐2 and IM7/5250‐4 graphite/epoxy cross‐ply [90₂/0₂]_S and angle‐ply [0/‐45/90/45/0/45090/‐45/0]_S laminates were tested using these systems. Ply‐by‐ply microcrack density was measured as a function of thermomechanical cycles. The second part of this article deals with effect of thermal gradients due to sudden exposure to a cryogenic temperature. The sudden exposure to cryogenic temperatures may have caused the microcracks, due to large temperature variations through the thickness and the resulting thermal stresses. In this work, an investigation of the sudden exposure to cryogenic temperatures is conducted experimentally with and without an insulating layer. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

The need to re‐evaluate laminate design criteria

The aerospace industry uses carbon‐fiber epoxy laminates for structures to reduce weight and increase payload. The “standard” design criterion for strength is that proposed by Tsai‐Wu. For stiffness, which is generally more critical than strength, classical laminated plate theory (LPT) is used. The normal lay‐ups considered for commercial aircraft are made up from 0°, 90° and ± 45° orientations. Angle ply laminates, [± ϕ]_ns, with ϕ fixed to some angle such as 20°, are not normally used (although this type of structure is employed with great success in the pressure vessel industry). According to the Tsai‐Wu criterion, such a structure should be extremely weak, which probably accounts for the absence of simple angle ply structures in aerospace designs. However if short and wide samples (aspect. ratio 0.5 or less) are tested, higher values are obtained for modulus and much higher values for strength than the long narrow samples used to develop the Tsai‐Wu criterion. The short and wide sample test results are in agreement with results from tests on tubes. These observations show that there is an “edge softening” effect: long narrow samples have a relatively large amount of this soft edge. Since design software normally uses Tsai‐Wu and LPT, large errors in strength and significant errors in stiffness are possible at this stage, and better lay‐up designs may be totally missed. The experimental work leading to these conclusions is described and innovative designs are discussed.     

Experimental failure analysis of two‐serial‐bolted composite plates

In this study, a failure analysis of two‐serial‐bolted glass‐fiber‐reinforced epoxy composite plates was performed. To determine the influences of the joint geometry and stacking sequences on the bearing strength and failure mode, parametric studies were carried out experimentally. Three different geometrical parameters—the ratio of the edge distance to the hole diameter (E/D), the ratio of the plate width to the hole diameter (W/D), and the ratio of the distance between two holes to the hole diameter (K/D)—were considered. For this reason, the E/D, W/D, and K/D ratios were designed to range from 1 to 5, from 2 to 5, and from 3 to 5, respectively. Furthermore, the tests were performed with various preload moments (2, 3, 4, and 5 Nm) and without any preload moments (0 Nm). Because of the observed effect of the material parameters on the failure behavior, composite laminated plates were stacked in two different stacking sequences: [0°/0°/30°/30°]_s and [0°/0°/45°/45°]_s. The experimental results indicated that the failure response of the two‐serial‐bolted joints were strictly affected by the material parameters, geometrical parameters, and values of the applied preload moments. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Damage development in a noncrimp‐glass fabric reinforced epoxy composite material

The relationship between textile architecture and the damage sequence under tensile loading has been investigated experimentally for a composite material reinforced with a noncrimp glass‐fiber textile of configuration [0°, +45°, 90°, −45°] stacking sequence based on epoxy resin matrix cured with high‐temperature hardener. The system chosen for this work consists of a bifunctional epoxy, diglycidyl ether of bisphenol A, cured with a tetrafunctional amine, diaminodiphenyl sulfone (DDS). This system ensures to obtain a rigid material with excellent mechanical properties in order to observe, analyze, and identify the process and progress of the generated damage and the failure mechanism which leads to the materials fracture. The properties have been studied for each ply direction at 0°, +45°, 90°, and −45° in order to make a comparative assessment of the influence of the polyester (PES) yarns in zig‐zag and unidirectional geometry, that hold together the four plies in the textile, in the composite damage generation. The laminates were uniaxially tensile loaded until final fracture occurred. It was found that PES threads have an effect on cracking progression depending on the textile orientation. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Delamination characteristics of multi‐directional carbon fiber/epoxy composites under high pressure

It was shown in a previous study that for unidirectional (0‐deg) graphite/epoxy composites, the fracture toughness under hydrostatic pressure increased 38% as hydrostatic pressure increased from 0.1 MPa to 200 MPa. This work investigates the compressive delamination behavior of multi‐directional graphite/epoxy laminated composites subjected to various hydrostatic pressures. Compressive delamination tests were performed under four hydrostatic pressure levels: 0.1, 100, 200, and 300 MPa Eighty‐eight‐ply dog‐bone type specimens with a single delamination at the center of the specimen were used. The stacking sequence applied was [0°/±45°/90°]_lls. The compliance and fracture load were determined from load‐displacement curves as a function of hydrostatic pressure. The results show that the compliance decreases with increasing pressure while fracture load increases with increasing pressure. The compressive delamination toughness, G_c, was determined from the compliance method as a function of applied hydrostatic pressure. The results also show that G_c is significantly affected by hydrostatic pressure and increases from 2.11 kJ/m² to 3.04 kJ/m2 (44% increase) as hydrostatic pressure increased from 0.1 MPa to 300 MPa. Visual examination of the fractured surface revealed that the increase of G_c is due to the suppression of micro‐cracks With increasing pressure. It was also found from SEM examination of delaminated surface that the G_c increase is due to more epoxy adhering to the fibers and more plastic deformation of epoxy material as applied hydrostatic pressure increases.     

Effects of thermal and mechanical fatigue on flexural strength of G40-600/PMR-15 cross-ply laminates

The effects of thermal and mechanical fatigue on the flexural strength of G40-600/PMR-15 cross-ply laminates with ply orientations of (0₂, 90₂)_2s and (90₂, 0₂)_2s are examined. The relative improtance of shear and tensile stresses is examined by varying the span-to-depth ratios of flexural test specimens from 8 to 45 Acoustic emission singals are measured during the flexural tests in order to monitor the initiation and growth of damage. Optical microscopy is used to examine speciments for resin cracking, delamination, and fiber breaks after testing. Transverse matrix cracks and delaminations occur in all specimens, for regardless of ply orientation, span-to-depth ratio, or previous exposure of specimens to thermal and mechanical fatigue. A small amount of fiber tensile fracture occurs in the outer 0° ply of specimens with high span-to-depth ratios. Because of the complex failure modes, the flexural test results represent the “apparent” strengths rather than the true flexural or shear strenghts for these cross-ply laminates. Thermal cycling of specimens prior to flexural testing does not reduce the apparent flexural strength or change the mode of failure. However, fewer acoustic events are recorded at all strins during flexural testing of specimens exposed to prior thermal cycling. High temperature thermal cycling (32–260°C, 100 cycles) causes a greater reduction in acoustic events than low temperature thermal cycling (?85 to 85°C, 500 cycles). Mechanical cycling (0–50% of the flexural strength, 100 cycles) has a similar effect, except that acoustic events are reduced only at strains less than the maximum strain applied during flexural fatigue. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

胶接面纤维铺层角度对复合材料胶接应力和强度影响分析

为研究复合材料胶接面铺层对接头强度的影响,以单搭接接头为研究对象,通过铺层设计使接头的被粘物具有相同的拉伸模量和弯曲模量,但胶接面的铺层角度不同,使用有限元法对不同铺层的接头进行建模,分析接头胶接面和胶层的应力,引入Tsai-Wu失效因子对胶接面铺层进行评估。结果表明:胶接面铺层角度对应力分布有一定影响,0°胶接面会造成较大的胶层应力,但胶接面的应力和失效因子较小;90°铺层下胶层应力最小,但胶接面的应力和失效因子水平较高;45°下胶接面的失效因子和胶层应力水平介于两者之间。通过与实验结果对比,得出了胶接面铺层角度影响接头强度及破坏模式的一般性规律。     

Counterion‐Switched Reversibly Hydrophilic and Hydrophobic TiO2‐Incorporated Layer‐By‐Layer Self‐Assembled Membrane for Nanofiltration

The manipulation of surface wettability has been regarded as an efficient strategy to improve the membrane performances. Herein, the counterion‐switched reversibly hydrophilic and hydrophobic surface of TiO₂‐loaded polyelectrolyte membrane are prepared by layer‐by‐layer assembly of poly(sodium 4‐styrene sulfonate) (PSS) and poly(diallydimethyl‐ammoniumchloride (PDDA) containing TiO₂@PDDA nanoparticles (NPs) on the hydrolyzed polyacrylonitrile (PAN) substrate membrane. The obtained polyelectrolyte multilayer (PEM) membranes [PEM‐TiO₂]_4.5⁺X^? (X^? = Cl^?, PFO^? [perfluorooctanoate] etc.) show different hydrophilicity and hydrophobicity with various counterions. The integration of TiO₂ NPs obviously improves the wettability and nanofiltration (NF) performance of PEM membrane for (non)aqueous system of dyes (crystal violet, eriochrome black T) with a high recyclability. The highly hydrophilic [PEM‐TiO₂]_4.5⁺Cl^? (water contact angle [WCA]: 13.2 ± 1.8°) and hydrophobic [PEM‐TiO₂]_4.5⁺PFO^? (WCA: 115.4 ± 2.3°) can be reversibly switched via counterion exchange between Cl^? and PFO^?, verifying the surface with a reversible hydrophilic–hydrophobic transformation. For such membranes, the morphology, wettability, and NF performance rely on the loading of TiO₂@PDDA NPs and surface counterion. Meanwhile, the motion and interaction of water or ethanol in the hydrophilic or hydrophobic membrane are revealed by low‐field nuclear magnetic resonance. This work provides a facile and rapid approach to fabricate smart and tunable wetting surface for potential utilization in (non)aqueous NF separation.     

Low Temperature‐Based Flexural Properties of Carbon Fiber/Epoxy Composite Laminates Incorporated with Carbon Nanotube Sheets

This study introduces carbon nanotube buckypaper (CNTBP) into the easily fractured sites of [0°]₁₆ and [0°/90°]_4S composite laminates, and comparatively explores how the CNTBP affects the flexural properties of the laminates at 25, ?15, and ?55 °C. Compared to the base [0°]₁₆ and [0°/90°]_4S laminates at the same temperature, improvements of the flexural strengths in the order of 4.0–15.3% and 6.5–31.0% are respectively obtained from the corresponding CNTBP‐reinforced [0°]₁₆ and [0°/90°]_4S laminates. Importantly, the lower the temperature is, the higher the strength improves. In fact, the CNTBP has little effect on the flexural moduli of the studied laminates, although there is an increasing trend with decreased temperature. Moreover, the introduced CNTBP would significantly change the fracture mechanism of the laminates at low temperature. The present work reveals that the CNTBP exhibits more positive reinforcing capability to the polymer matrix‐based composite laminates at relatively low temperatures.     

Investigation of production parameters in fracture behavior of hot-pressed Al2O3–SiC/graphite fibrous monolithic ceramics: Fibers orientation and cell boundary fraction

Fibrous monoliths (FMs) exhibit graceful failure in flexure and have higher toughness values. In this research, a mixture of Al₂O₃ and SiC as the core and graphite as the shell material of fibers were produced by extrusion-molding technique and after aligning along intended directions (0°, 90°, and 0°/90°) were sintered using the hot-pressing method at the temperature of 1500°C under pressure of 35 MPa for 1 hour. The significance of fibers orientation angle and the cell to cell boundary volume ratio in defining the fracture behavior of the FMs was detected. Because of the extensive crack interactions with graphite cell boundary such as crack deflection and delamination, with increasing cell boundary content from 25 to 30 vol%, the fracture toughness was enhanced. The highest flexural strength (184.8 ± 0.61 MPa) obtained from samples with 0° fibers orientation compared to 0°/90°. Since in the transverse plies (layers with 90° aligning), the properties of matrix phase are dominant, hence the strength in specimens with 0°/90° fibers orientation decreased considerably due to weak graphite matrix phase. In addition, the fracture toughness value increased up to 8.35 ± 0.74 MPa·m^1/2 for the unidirectional architecture of (0°) in comparison with cross-ply (0°/90°) architecture.     

Micro‐Driving behavior of carbon‐fiber‐reinforced epoxy resin for standing‐wave ultrasonic motor

The application of the friction drive of carbon‐fiber‐reinforced composites to a standing‐wave ultrasonic motor was investigated. Friction drive tests were conducted on carbon‐fiber‐reinforced epoxy resins (CF/epoxy) by home‐made test rig, which was based on plate‐rod vibrator. The effects of fiber orientation and ply thickness on dynamic drive and dynamic normal forces were investigated. Fiber orientation angle and ply thickness affected friction drive. Different dynamic drive forces, which varied both in amplitude and period, were observed for CF/epoxy composites with different winding angles. A CF/epoxy composite with a winding angle of 30° showed the largest dynamic drive force (∼0.45 N) and the shortest contact period (∼26 μs). The period of dynamic normal force was uniform (∼65 μs) for various CF/epoxy composites. Wear traces of different composites exhibited different wear modes, such as scuffing, peeling, and shearing. The anisotropic property of CF/epoxy material affected the drive process of standing‐wave ultrasonic motor. The current study taking the carbon‐fiber‐reinforced epoxy resin as an example of anisotropic materials arise more enough attention on inexpensive, biodegradable, and renewable alternatives for the efficient and durative drive of a standing‐wave ultrasonic motor. POLYM. COMPOS., 37:2152–2159, 2016. © 2015 Society of Plastics Engineers     

Failure behaviour of the single lap joints of angle-plied composites under three point bending tests

Abstract

In this paper, the response of adhesively-bonded single lap joints (SLJs) with angle-plied composite adherends subjected to flexural loading was investigated. The experiments were carried out for the adherends, glass reinforced polymer matrix, with three kinds of stacking sequence. A three-dimensional finite element (FE) model was developed using ABAQUS/Explicit. The three dimensional Hashin failure criterion with an appropriate damage evolution law was used to characterize the damage inside a ply. Cohesive zone elements were used to model the damage in the adhesive layer (AF163-2K) and the interply failure, that is, the delamination. The developed numerical model was verified with the performed experiments. The SLJs of [±20]_5s and [±45]_5s failed due to failure in the adhesive layer and the delamination between the plies, whereas that of [±10]_5s failed mainly due to the former failure. The intralaminar damage was not noticed for any case. The influence of the fiber angle of plies in the adherends, adherend thickness, overlap length, and the thickness of adhesive layer on the damage in the adhesive layer and the delamination were investigated in terms of the competition between these two failures and activation of different failure modes in each thoroughly.     

Hybridization effects on lateral buckling behavior of laminated composite beams

The aim of this study is to investigate the influence of hybridization on lateral buckling behavior of composite beams consists of symmetrical and unsymmetrical ply orientations, various cutout shapes, and length/thickness ratio. Carbon, S‐glass, and Aramid fibers are used as reinforcement with epoxy resin. Experiments are performed to see the effects of various combinations of fibers on lateral bucking loads with [(0/90)₃]_s, [(30/‐60)₃]_s, [(45/‐45)₃]_s symmetrical, and [(0/90)₆]_us unsymmetrical ply orientations. Numerical studies are also performed to see the effects of length/thickness ratio, and various cutout shapes on the lateral buckling loads using finite element analysis software ANSYS. It is concluded that stiffness and shear properties are affecting the lateral buckling characteristics of the composite beams. Also, fibers having higher stiffness and higher shear properties in the upper layers increase the lateral buckling strength. POLYM. COMPOS., 37:2511–2521, 2016. © 2015 Society of Plastics Engineers     

The effect of isothermal aging on transverse crack development in carbon fiber reinforced cross-ply laminates

An investigation into the effect of isothermal aging on the development of transverse cracks in cross-ply laminates of two high temperature composite systems was performed. The composite materials investigated were BASF X5260/640–800 and DuPont Avimid K/IM6. Changes in the glass transition temperature, composite weight loss, crack density, and mode I intralaminar fracture toughness were monitored during isothermal aging in air at 177°C for up to 2232 h. The two laminate configurations used in this study include two variations of the generic cross-ply configuration [0₂/90_n]_s, in which n equals 1 and 2. The results of this investigation show that a layer of degraded material forms at the surface of the X5260/640–800 bismaleimide laminates and that the thickness of the degraded layer increases with aging time. After 744 h of aging, transverse cracks form in the surface plies and an increasing crack density evolves as aging time is increased; however, transverse cracks do not form in the inner 90° ply groups with aging during the time period investigated. The Avimid K/IM6 thermoplastic polyimide laminates, which show evidence of cracking prior to aging, do not exhibit any significant change in crack density with aging. The results of the aging experiments also show that the bismaleimide system exhibits a weight loss of 1.5% and an increase in glass transition temperature from 250°C to 300°C after 2232 h of aging at 177°C, while the thermoplastic polyimide system shows a weight loss of only 0.05% and an increase in glass transition temperature from 280 to 285°C after 2232 h. Changes in the resistance to crack formation are also seen in these materials during aging. The mode I intralaminar fracture toughness, a measure of resistance to transverse crack formation, shows a 50% decrease after aging for 2232 h for the bismaleimide system, while the behavior exhibited by the thermoplastic polyimide shows little evidence of a reduction.     

Theoretical Analysis for Calculation of the Through Thickness Effective Constants for Orthotropic Thick Filament Wound Tubes

This paper presents a method for determining the theoretical values for all the elastic constants needed for three-dimensional stresses of angle-ply laminates and filament wound tube from the properties of unidirectional fiber reinforced epoxy resin. The layers were arranged symmetrically about the mid-surface of the laminate. The stress in the longitudinal axis is assumed to be constant throughout the thickness of the laminate. The results for the effective elastic constants versus filament winding angle from θ = 0° to θ = 90° for glass/epoxy composite are presented. The results show that the through thickness elastic modulus E _z did not change significantly with the winding angle. The E _x , E _y , and G _xy vary significantly with the winding angle of the tube θ. Out of plane shear modulus G _xz and G _yz also did not vary significantly with the winding angle of the tube θ.     

Investigation of the compaction behavior of carbon fiber NCF for continuous preforming processes

This paper describes the experimental investigation of the compaction behavior of dry single‐ply and multi‐ply fabric stacks (preforms). Utilizing four biaxial (two 0°/90° and two ±45°) and one triaxial (0°±45°) carbon fiber NCF, differing in weight (300 g/m², 600 g/m²) and type of stitching (tricot, pillar, hybrid), the influence of compaction speed, pre‐compaction cycles, number of layers, and stacking sequence on compaction force was examined. In contrast to other studies, the area of interest is limited to 40–50% fiber volume content (FVC), which is based on current continuous preforming conditions. The results showed that higher testing speeds result in increased compaction forces. Pre‐compaction cycles (up to 8) significantly reduce (up to 69%) the required compaction forces of preforms for continuous preforming. Furthermore, at an equal total superficial density (1800 g/m²), 6‐ply preforms (300 g/m² each ply) require 75–88% higher compaction forces than 3‐ply preforms (600 g/m² each ply). This relation remains constant with decreasing or increasing total superficial density (ply number). Also the stacking sequence of 6‐ply preforms (300 g/m² each ply) remarkably influences the compaction force, whereby the stitching seam pattern and their alignment (superposition) to each other were the main influencing factors. POLYM. COMPOS., 38:2609–2625, 2017. © 2015 Society of Plastics Engineers     

Mass transfer from cylinders at various orientations to flowing gas streams

The effects of angle of cylinder orientation and cylinder length on mass transfer rates were studied for Reynolds numbers ranging from 6,000 to 18,000. Orientations (?) varied from 0° to 90° for cylinders whose L/D's ranged from 5.26 to 21.04. The relation j_m = m(N Re)ⁿ fit the data for a given orientation and L/D. Both j_m and N_Nu, data compared favorably to literature values for transverse and parallel flow. Sherwood numbers were shown to be [1] a function of (N Re × sin ?) [2] to correlate with Consin's “cosine law” and [3] to be a function of L and ?. Peak mass transfer occurred between 45° and 75°.