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。     

Experimental study on the mechanical behavior and failure mechanism of 3d MWK carbon/epoxy composites under quasi‐static loading

Quasi‐static tensile, out‐of compression, in‐plane compression, three‐point‐bending and shear tests were conducted to reveal the mechanical behavior and failure mechanisms of three‐dimensional (3D) multiaxial warp‐knitted (MWK) carbon/epoxy composites. The characterization of the failure process and deformation analysis is supported by high‐speed camera system and Digital Image Correlation. The results show that tensile, bending, out‐of‐plane compression, in‐plane compression stress–strain response exhibit obvious linear elastic feature and brittle fracture characteristics, whereas the shear response exhibits a distinct nonlinear behavior and gradual damage process. Meanwhile, 3D MWK carbon/epoxy composites have good mechanical properties, which can be widely used in the fields of engineering. In addition, the failure for tension behaves as interlayer delaminating, 90/+45/−45° interface debonding and tensile breakage of 0° fibers; the damage for out‐of‐plane compression is mainly interlaminar shear dislocation together with local buckling and shear fracture of fibers; the failure pattern for in‐plane compression is 90° fiber separating along fiber/matrix interface as well as 0/+45/−45° fiber shear fracture in the shear plane. The main failure for bending is fiber/matrix interface debonding and fibers tearing on the compression surface, 0° fibers breakage on the tension surface as well as fiber layers delaminating. Although the shear behavior is characterized by a gradually growing shear matrix damage, 90/+45/−45° interface debonding, +45/−45° fibers shear fracture, and final 0° fiber compression failure. POLYM. COMPOS., 37:3486–3498, 2016. © 2015 Society of Plastics Engineers     

Off-axis tensile properties and fracture in a unidirectional graphite/polyimide composite (celion 6000/PMR 15)

Tensile properties of unidirectional Celion 6000 graphite/PMR 15 polyimide composites prepared by hot molding and cold molding processes were measured at room temperature and 316°C, the upper use temperature of the polyimide resin, at both 45 and 90° to the fiber axis. The resulting fractures were characterized by scanning electron microscopy and materialographic techniques. Variation in tensile properties with processing history occurred in the elastic modulus and strain to failure for specimens loaded at 90° at 316°C, and in the fracture stress, and hence the in-plane shear stress, for those loaded at 45° at room temperature. Significant plastic deformation was observed in the 45° orientation at 316°C for material produced by both processing methods. In general, fracture occurred by both failure within the matrix and at the fiber-matrix interface; the degree of interfacial failure increased with temperature. Secondary cracking below the primary fracture surface also was observed.     

The effect of fiber orientation on failure behavior of 3DN C/SiC torque tube

In this paper, the 3DN C/SiC torque tubes were fabricated by chemical vapor infiltration (CVI) combined with silicon melt infiltration (SMI) method with different fiber orientations (0°/90° and ± 45°) which leads to different density, torsional behaviors and failure behaviors. CT test was implemented to characterize the density heterogeneity. Using the density measured from Archimedes drainage method, FEM software was implemented to simulate the stress distribution of the tubes and calculate the failure stress. A good agreement with analytical model was obtained which helps a lot to failure analysis. Torsional tests were conducted using special attachments to a universal material test machine, the shear strain was calculated from the strain gauge, the shear strength was calculated by simplified formula, different torsional behaviors of two different fiber orientations were represented in the stress-strain curves. The fracture morphologies were observed by SEM, and the predominant factors of failure were analyzed. Torque tubes with fiber orientations of ± 45° have a higher torque capacity, modulus, and reasonable fracture morphologies, which is in good agreement with simulation results.     

The effects of fiber orientation on failure behaviors of 2D C/SiC torque tube

Different failure behaviors were observed in the 2D C/SiC torque tubes which were fabricated by chemical vapor infiltration (CVI) with different fiber orientations (0°/90° and ±45°). CT test was implemented to characterize the density heterogeneity of the ceramic matrix composite (CMC) torque tubes. With the density value measured by Archimedes drainage method, FEM software was implemented to simulate the stress distribution of the ceramic matrix composite torque tubes and calculate the failure stress. Torsional tests were conducted using special attachments to a universal material test machine. Different torsional behaviors of CMC torque tubes with two different fiber orientations were presented in the stress-strain curves. The fracture morphologies were observed by SEM, and the predominant factors of failure were analyzed. CMC torque tubes with fiber orientation of ±45° have a higher torque capacity and modulus. In failure analysis, we found that ±45° fiber orientation CMC torque tubes have reasonable fracture morphologies.     

Degradation of single lap adhesively bonded composite joints due to hot water ageing

Joints, which are the most critical part of fibre-reinforced epoxy plastic structures, can be exposed to continuous hydrothermal action. In order to estimate their long-term performance, an accelerated ageing process was performed on adhesively bonded joints of glass-fibre-reinforced epoxy plastics with [0/90/45/?45]_s fibre orientations. Changes in the static tensile properties of single lap shear samples due to hot-wet exposure were investigated for one- and two-week immersion periods and at three different water temperatures (50°C, 70°C, and 90°C). Both the ageing temperature and immersion time were found to be influential on load–displacement characteristics, maximum failure loads, and apparent failure modes of joints bonded with Loctite Hysol-9466 epoxy type adhesive. Due to the hydrothermal exposure, maximum failure loads, distance to failure values, and stiffness of joints decreased by a certain amount in proportion to the immersion time and temperature. While unaged samples and those aged at 50°C and 70°C exhibited mainly light fibre-tear (LFT) failures, the samples treated at 90°C ruptured through the material cross section in stock-break (SB) failure mode.     

In-plane shearing stress–strain response of glass-fiber-reinforced composites as determined from four-point bending tests

In this article an experimental study to determine the longitudinal (or in-plane) shearing stress–strain response of a unidirectional fiber-reinforced composite material is presented. The test method used is the four-point blending of a ±45° off-axis glass-fiber-reinforced laminate. Although a laminate is used for the investigation of the shearing stress–strain response, it is shown that unidirectional shear properties can be found from the laminate test data following a procedure analogous to that used in previously. Also, the 45° off-axis test of unidirectional composite in bending was carried out to obtain the in-plane shear modulus and compare it with that obtained by the ±45° off-axis method. Finally both values were compared with the theoretical value of the in-plane shear modulus obtained from a theoretical formula where the concept of boundary interphase between fiber and matrix was introduced. © 1995 John Wiley & Sons, Inc.     

Strength of adhesive joints with adherend yielding: II. Peel experiments and failure criteria

Peel tests were conducted with an epoxy adhesive on nine rigid-flexible peel configurations: combinations of 1, 2, and 3 mm aluminum adherend thickness and 30°, 60°, and 90° peel angle. The peel model described in an accompanying paper was used to calculate the stress and strain distributions in the adhesive, the strain energy release rates, and the root curvature of the adherend corresponding to steady-state peel failure. Two failure criteria were examined: the critical von Mises strain and the critical fracture energy, G c . The first criterion was found to be essentially independent of the peel angle but dependent on the thickness of the peel adherend. It produced predictions of the peel force that had an average error of 11%. The fracture energy criterion showed that G c depended on the average phase angle of the loading. This criterion was preferred, having an average prediction error of 6% over the nine experimental cases, and requiring fewer free parameters.     

Strain response and damage modelling of glass/epoxy pipes under various stress ratios

Abstract

This paper presents the stress–strain response and general lifetime damage modelling of glass fibre reinforced epoxy (GRE) composite pipes subjected to multi-ratios stress loadings at room temperature (RT). This particular modelling work was developed to predict the non-linear stress–strain response caused by the fatigue static and cyclic loading in the multiaxial ultimate elastic wall stress (UEWS) tests by considering the effects of matrix cracking within the laminates. Although the UEWS procedure is not a standard protocol used for qualification of GRE pipes, it appears to offer an option to existing procedures delineated in ASTM D2992. The ply properties initially expressed as a function of crack density was computed as a function of increasing stress and strain using shear lag approximation. In general lifetime damage model, the effects of stress developed in each ply from ultimate elastic wall stress (UEWS) test were expressed in a single quadratic term of axial and hoop stress. The term then solved to produce limits with respect to axial and hoop stress, which represented in a graphical form of failure envelope. The predictions from both models are found to be in good agreement with the data from the multiaxial UEWS tests of ±55° filament wound GRE pipes. These models thus enable for the long term performance prediction of the pipes under combined loadings.     

The effect of fast neutron irradiation on the compressive stress-strain relationships of graphite

A study of the effects of fast neutron irradiation on the mechanical properties of polycrystalline graphite is reported. Irradiation to a maximum dose of 1.14 × 10¹⁹ n/cm² at ～ 50°C increased the Young's modulus by 140%. The linearity of the compressive stress-strain curve increased and the hysteresis losses decreased. The fracture stress doubled, whilst the fracture strain decreased by ~24%. Measurements of the total energy absorbed in compression indicated an average increase in the energy required for failure after irradiation. A constant elastic strain to failure criterion was found to be applicable for these irradiation conditions. Upon subsequent thermal annealing the Young's modulus decreased and had almost reached its unirradiated value by 400°C. The fracture stress also decreased towards its unirradiated value and the hysteresis losses increased.     

Film‐insert injection compression molding for reinforced polycarbonate with woven glass fiber oriented 90/0°, ± 45°

A manufacturing method is proposed using two conventional methods, film insert molding and compression molding, to obtain rectangular of the size of 250 × 35 × 2.5 mm specimens of polycarbonate reinforced with 4% mat fibers glass with orientations 90/0° and ±45°, to investigate, disorientation of the fibers. A Finite Element Method was performed, using Moldflow to determine initial conditions to predict the behavior of the polymer during the compaction stage and then manufacture the mold. Physical tests were performed using a conventional injection machine, based on the results previously obtained in the simulation. Woven fiberglass did not require a chemical treatment previously to achieve adhesion between the two types of polycarbonate. Specimens of polycarbonate reinforced at 0/90° and ±45° orientation have demonstrated small fiber orientation distortion. For the case of 0/90° specimens, the maximum deviation is show in the specimen with 2.58° which represent a misalignment cause by compression stage which also happened in 0° where the maximum standard deviation is 0.98°. Measurements for the +45° fibers, the standard deviation is 2.60° and 2.23° for ?45°. According to ASTM D3039, the deviation of fiber, are within the tolerance to be characterized and obtain the mechanical properties. POLYM. ENG. SCI., 59:E372–E379, 2019. © 2019 Society of Plastics Engineers     

Manufacture and thermomechanical characterization of wet filament wound C/C-SiC composites

The paper presents manufacture of C/C-SiC composite materials by wet filament winding of C fibers with a water-based phenolic resin with subsequent curing via autoclave as well as pyrolysis and liquid silicon infiltration (LSI). Almost dense C/C-SiC composite materials with different winding angles ranging from ±15° to ±75° could be obtained with porosities lower than 3% and densities in the range of 2 g/cm³. Thermomechanical characterization via tensile testing at room temperature and at 1300°C revealed higher tensile strength at elevated temperature than at room temperature. Thus, C/C-SiC material obtained by wet filament winding and LSI-processing has excellent high-temperature strength for high-temperature applications. Crack patterns during pyrolysis, microstructure after siliconization, and tensile strength strongly depend on the fiber/matrix interface strength and winding angle. Moreover, calculation tools for composites, such as classical laminate and inverse laminate theory, can be applied for structural evaluation and prediction of mechanical performance of C/C-SiC structures.     

Evaluation of dynamic modulus measurement for C/C-SiC composites at different temperatures

The determination of elastic properties at application temperature is fundamental for the design of fibre reinforced ceramic composite components. An attractive method to characterize the flexural modulus at room and high temperature under specific atmosphere is the nondestructive Resonant Frequency Damping Analysis (RFDA). The objective of this paper was to evaluate and validate the modulus measurement via RFDA for orthotropic C/C-SiC composites at the application temperature. At room temperature flexural moduli of C/C-SiC with 0/90° reinforcement were measured under quasi-static 4-point bending loads and compared with dynamic moduli measured via RFDA longitudinally to fibre direction. The dynamic modulus of C/C-SiC was then measured via RFDA up to 1250°C under flowing inert gas and showed an increase with temperature which fitted with literature values. The measured fundamental frequencies were finally compared to those resulting from numerical modal analyses. Dynamic and quasi-static flexural moduli are comparable and the numerical analyses proved that bending modes are correctly modeled by means of dynamic modulus measured via RFDA. The nondestructive RFDA as well as the numerical modeling approach are suitable for evaluation of C/C-SiC and may be transferred to other fibre reinforced ceramic composite materials.     

Additive manufacturing of carbon fiber reinforced ceramic matrix composites based on fused filament fabrication

For the first time, carbon fiber reinforced ceramic matrix composites (CMC) were successfully fabricated by additive manufacturing (AM) using the fused filament fabrication (FFF) technology, filaments (“CF-PEEK”) with thermoplastic polyetheretherketone (PEEK) as the matrix and C-precursor, and carbon short-fibers (< 250 μm) as reinforcements. In order to prevent a re-melting of the as-printed CFRPs (C-fiber reinforced plastics) during pyrolysis at 1000 °C in N₂ensuring the freedom of design and complex parts, a prior crosslinking step at 325 °C with a dwell time of 48 h in air was introduced to stabilize and crosslink the CFRP. Due to the stabilization and the printing of degassing channels for the pyrolysis, near net shape and complex CMC parts with different C-fiber orientations (0°; ±45°; 90°) were obtained by the liquid siliconization infiltration process (LSI). The manufactured C/C-SiC parts were characterized regarding their microstructure and mechanical properties. The reinforcing C-fibers were successfully protected during the LSI-process and flexural strengths of almost 60 MPa were obtained.     

复合材料沉头搭接强度与渐进损伤研究

基于三维渐进损伤理论,引入Tserpes失效准则及其改进的材料性能退化准则,建立复合材料沉头搭接结构的有限元模型。在试验验证数值仿真模型正确性的基础上,探讨了端距、板宽及拧紧力矩对接头强度的影响,并对搭接接头从初始损伤到最终失效的过程进行可视化模拟。结果表明,端径比由2到4、宽径比由3到5、拧紧力矩由0到5.9 N·m的过程中,接头强度明显增强,超过上述范围,强度增加不明显或不再增加。在静拉伸过程中,2号钉孔处复合材料板的损伤程度要比1号钉孔处严重,且2号钉孔的损伤扩展导致接头最终失效;90°铺层最先产生损伤,其类型主要为基体开裂,0°铺层损伤情况最弱,±45°铺层沿着-45°方向产生基体开裂,随后沿板宽方向产生大量纤维断裂。     

Application of a necking criterion to PET fibers in tension

A criterion to predict instability in rate‐dependent materials is developed. It is implemented for PET fibers in tension at three temperatures: 60, 75, and 80°C. At 60°C, necking is always observed, whereas at 80°C, the deformation is uniform, and 75°C marks a transition region, where necking is observed only at higher speeds and the deformation is otherwise uniform. As a necessary tool in the implementation of this criterion, the stress–strain behavior of PET is modeled using a combination of an Eyring process, a Gaussian network, and a linear elastic element. The resulting instability model gives predictions that are generally consistent with the experimental observations at all temperatures. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3331–3341, 1999     

Characterization and modeling of tensile properties of continuous fiber reinforced C/C-SiC composite at high temperatures

In order to study the effects of temperature on the material behavior of Liquid Silicon Infiltration (LSI) based continuous carbon fiber reinforced silicon carbide (C/C-SiC), the mechanical properties at room temperature (RT) in in-plane and out-of-plane directions are summarized and the tensile properties of C/C-SiC were then determined at high temperature (HT) 1200 °C and 1400 °C under quasi static and compliance loading. The stress-strain response of both HT tests is similar and almost no permanent strain can be observed compared to the RT, which can be explained through the relaxation of residual thermal stresses and the crack distribution under various states. The different fracture mechanisms are confirmed by the analysis of fracture surface. Furthermore, based on the analysis of hysteresis measurements at RT, a modeling approach for the prediction of material behavior at HT has been developed and a good agreement between test and modeling results can be observed.     

Review of failure criteria of fibrous composite materials

Composite materials exhibit various and complex failure behavior. Different formalisms have been used to predict failure. Improvement of old theories and new ones continue to be published. In this paper, the most recent and widely used models are presented. Failure criteria such as Tsai-Wu, parametric formulations, maximal stress and strain, Hashin criterion, Hart-Smith criterion, and the method based on kriging are presented. These failure theories may be classified in two categories, depending whether they integrate failure modes or not. The formalism of each theory is briefly described and their application to model failure of composite laminates is discussed by comparing the advantages and limitations of each method. The diversity of experimental failure envelopes, as reported in the literature on composites, is outlined and it is shown that most criteria permit modeling only particular failure properties of composite laminates.     

Microstructure and mechanical properties of reaction bonded B4C-SiC composites: The effect of polycarbosilane addition

Reaction bonded B₄C-SiC composites were prepared by infiltrating silicon melt into porous B₄C-SiC green preforms at 1500 °C in vacuum. The porous green preform was obtained from a mixture of polycarbosilane (PCS) and particle size graded B₄C after pre-sintering at 1600 °C. For the first time, PCS was used to adjust the phase composition and microstructure of the reaction bonded boron carbide composites. It is indicated that the addition of PCS and its content has a significant influence on the microstructure as well as the mechanical properties of the subsequent reaction bonded B₄C-SiC composites. For the B₄C-SiC composite with 5 wt% PCS added, a flexural strength of 319±12 MPa, and an elastic modulus of 402±18 GPa can be achieved, which is 23% and 15% higher than those of the composite without PCS addition, respectively. While, with the higher content of PCS addition, the mechanical properties of the composites are decreased drastically due to the large amount of residual Si agglomeration in the composites. The reaction mechanisms as well as their microstructure evolution processes correlated with the mechanical properties of the reaction bonded B₄C-SiC composites are further discussed in our work.     

Failure of elastic‐plastic core–shell microcapsules under compression

Characterization of the failure behavior of microcapsules is extremely important to control the release of their core actives by mechanical forces. The strain and stress of elastic‐plastic uninflated core–shell microcapsules at failure (rupture or bursting) has been determined using finite element modeling (FEM) and micromanipulation compression experiments. The ductile failure of polymeric microcapsules at high deformations is considered to occur when the maximum strain in the shell exceeds a critical strain, resulting in their rupture. FEM has been used to determine the maximum strains present in the capsule wall at different deformations for three types of shell material: elastic, elastic—perfectly plastic and elastic—perfectly plastic with strain hardening at large strains. The results obtained were used to determine the failure strain and stress of melamine‐formaldehyde microcapsules, with average population values of ～0.48 and ～350 MPa, respectively. Thus, the elastic‐plastic stress–strain relationship has been determined for the core–shell microcapsules tested. © 2011 American Institute of Chemical Engineers AIChE J, 2012