Effect of fiber orientation on interfacial fracture toughness for adhesively bonded composite plates

In this study, interfacial fracture toughness was investigated experimentally and numerically in laminated composite plates with different fiber reinforcement angles bonded with adhesive. The composite plates are four-layered and the layer sequence is [0º/θ]_s. DCB test was applied to composite plates reinforced with epoxy resin matrix and unidirectional carbon fiber. The experimental sample model for the DCB test was made using the ANSYS finite element package program. In the numerical study, four layered composites were prepared in three dimensions. Under critical displacement value; mode I fracture toughness at the crack tip was calculated using VCC (virtual crack closure) technique. Numerical values consistent with experimental results have presented in graphical forms. At 60o and 75° the greatest fracture toughness was obtained. In addition, numerical results have shown that fiber orientation prevents the uniform distribution of stress on the interface crack tip and causes stress accumulation, especially at the edge of the plate.

     

The effect of fiber oxidation on the tribological behavior of 3D-braided carbon fiber/nylon composites

To investigate the influence of carbon fiber oxidation on the tribological behavior of the 3D-braided carbon fiber/nylon composites (C_3D/MCN), C_3D/MCN composites were prepared. The characteristics of carbon fibers with different conditions were characterized. The mechanical property, friction and wear tests of the composites with untreated and treated carbon fabric were performed and the worn surface morphology and wear debris were analysed. The results show that the specific surface area of the treated carbon fiber was far higher than that of the untreated carbon fiber and there formed a functional group of –CO on the carbon fiber surface after air oxidation. The flexural strength, flexural modulus and shear strength of C_3D/MCN composites with oxidized carbon fiber fabric were improved. The friction coefficient and wear rate of C_3D/MCN composites with oxidized carbon fiber fabric were apparently lower than that with untreated carbon fiber fabric. In conclusion, the surface treatment favored the improvement of the higher interface strength and so had good effect on improving the tribological properties of the composites.     

Effect of postpeak tension-softening behavior on the fracture properties of 2-D carbon fiber reinforced carbon composite

The fracture properties of commercial carbon fiber reinforced carbon (C/C) composites (CCM190C, CCM191C) that have different interfacial shear strength were investigated. Postpeak tension-softening phenomena were observed through the fracture mechanics test for these composites. The failure manner in the fracture process zone was primarily fiber pull-out for CCM190C and fiber breakage for CCM191C, respectively. It was confirmed that the scale of pseudo strain hardening for CCM190C with low interfacial shear strength was larger than that of CCM191C. The bridging energy at the postpeak part and the total energy consumed to produce a unit area of fracture surface were calculated based on the J-based technique. The bridging energy at the postpeak part accounted for 12.3% of the total energy consumed to produce a unit area of fracture surface for CCM190C. From this result, it can be deduced that the effect of the postpeak bridging energy on the fracture toughness is large for CCM190C. In contrast, the contribution of the postpeak bridging energy for the total energy per fracture surface was very small for CCM191C. This paper was recommended for publication in revised form by Associate Editor Chongdu Cho Yonjig Kim received B. S. and M. S. degrees in Mechanical Design Engineering and Mechanical Engineering at Chonbuk National University in 1983 and 1985, respectively. He enlisted in the army as a soldier and leaved the army in 1988, and then got a ph. D. degree in Mechanical Engineering at Chonbuk National University in 1993. Dr. Kim is currently working as a professor in his alma mater, Chonbuk National University. His major area of study is materials and fracture mechanics and he is interested mainly in fracture of fiber reinforced polymer composites.     

Influence of Plasma Treatment on Carbon Fabric for Enhancing Abrasive Wear Properties of Polyetherimide Composites

Interfacial adhesion between matrix and fiber plays a crucial role in controlling performance properties of composites. Carbon fibers have major constraint of chemical inertness and hence limited adhesion with the matrix. Surface treatment of fibers is the best solution of the problem. In this work, cold remote nitrogen oxygen plasma (CRNOP) was used for surface treatment. Twill weave carbon fabric (CF) (55–58 vol%) was used with and without plasma treatment with varying content of oxygen (0–1%) in nitrogen plasma to develop composites with Polyetherimide (PEI) matrix. The composites were developed by compression molding and assessed for mechanical and tribological (abrasive wear mode) properties. Improvement in tensile strength, flexural strength, and interlaminar shear strength (ILSS) was observed in composites due to treatment. Similarly, improvement in wear resistance (W _R) and reduction in friction coefficient (μ) were observed in treated fabric composites when slid against silicon carbide (SiC) abrasive paper under varying loads. A correlation between wear resistance and tensile strength was slightly better than that in Lancaster–Ratner plot indicating that ultimate tensile strength (S) and elongation to break (e) were contributing to control the W _R of the composites. It was concluded that enhanced adhesion of fibers with matrix was responsible for improvement in performance properties of composites, as evident from SEM, Fourier Transform Infrared spectroscopy-Attenuated Total Reflectance (FTIR-ATR) technique.     

Toughness and fracture mechanisms of glass fiber/aluminum hybrid laminates under tensile loading

Tensile properties and fracture toughness of monolithic aluminum (Al), glass fiber reinforced plastics (GFRPs) and glass fiber/aluminum hybrid laminates (GFMLs) were examined in relation to the fracture processes of plain coupon and single-edge-notched specimens. Elastic modulus and ultimate tensile strength of GFMLs showed characteristic dependences on the kind of Al, fiber orientation and the Al/fiber layer composition ratio. Fracture toughnesses K_C and G_C of A-GFML-UD were comparable to those of GFRP-UD and were much superior to monolithic Al. However, GFML with a transverse crack parallel to the fiber layer deteriorated largely in toughness. Microscopic observation of the fracture zone in the vicinity of the crack tip revealed various modes of micro-cracks in the respective layers as well as fiber fractures and delamination between fiber/Al layers. Such damage advances in GFMLs dependent on the orientation of the fiber layer and the Al/fiber composition ratio strongly influenced the strength and toughness of GFMLs.     

Fabrication of two-layered Al-B4C composites by conventional hot pressing uuder nitrogen atmosphere and their characterization

In this study, we describe the conventional hot pressing (CHP) of layered Al-B₄C composites and their characterization. The matrix alloy A1-5 wt.%Cu was prepared from elemental powder mixtures. The metal and B₄C powders were mixed to produce either Al-Cu-10vol.%B₄C or Al-Cu-30vol.%B₄C combinations. Then, these powder mixtures were stacked as layers in the hot pressing die to form a two-layered composite. Hot pressing was carried out under nitrogen atmosphere to produce 30×40×5 mm specimens. Microstructural features and age hardening characteristics of composites were determined by specimens cut longitudinally. The flexural strength of both layered composites and their monolithic counterparts were investigated via three point bending tests. In the case of layered specimens of both 10vol.%B₄C and 30vol.%B₄C containing layers were loaded for three-point test. The results show that a homogeneous distribution of B₄C particles in the matrix alloy which is free of pores, can be obtained by CHP method. The ageing behavior of the composites was found to be influenced by the reinforced materials, i.e. higher hardness values were reached in 8 hrs for the composites than that for the matrix alloy. Flexural strength test showed that two-layered composites exhibited improved damage tolerance depending on layer arrangement. Microstructural investigation of the fracture surfaces of the bending specimens was performed by means of scanning electron microscope (SEM). While layer with lower reinforcement content exhibited large plastic deformation under loading, the other with higher reinforcement content exhibited less plastic deformation.     

Manufacturing and mechanical characterization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/β-TCP/TiO<Subscript>2</Subscript> biocomposite as a potential bone substitute

This paper focuses on the mechanical characterization of a bioceramic based on commercial alumina (Al₂O₃) mixed with synthesized tricalcium phosphate (β-TCP) and commercial titania powder (TiO₂). The effect of β-TCP and TiO₂ addition on the mechanical performance was investigated. After a sintering process at 1600 °C for 1 h, various mechanical properties of the samples have been studied, such as compressive strength, flexural strength, tensile strength, elastic modulus, and fracture toughness. The measurements of the elastic modulus (E) and the tensile strength (σ _t ) were conducted using the modified Brazilian test while the compressive strength (σ _c ) was determined through a compression test. Also, semi-circular bending (SCB) specimens were used to evaluate the flexural strength (σ _f ) and the opening mode fracture toughness (K _IC). From the main results, it was found that the best mechanical performance is obtained with the addition of 10 wt.% TCP and 5 wt.% TiO₂. Alumina/10 wt.% tricalcium phosphate/5 wt.% titania composites displayed the highest values of mechanical properties and a good combination of compressive strength (σ _c ?≈?352 MPa), flexural strength (σ _f ?≈?98 MPa), tensile strength (σ _t ?≈?86.65 MPa), and fracture toughness (K _IC?≈?13 MPa m^1/2).     

Evaluation on the fracture toughness and strength of fiber reinforced brittle matrix composites

It is well known in the fracture mechanics community that the performance of brittle materials, such as different types of ceramics which have low fracture toughness, improves significantly when fibers are added into the material. This is because the presence of fibers deters the crack propagation. Fibers bridge the gap between two adjacent surfaces of the crack and reduce the crack tip opening displacement, thus make it harder to propagate. Several investigators have experimentally studied how the length, diameter and volume fraction of fibers affect the fracture toughness of fiber reinforced brittle matrix composite materials. However, to this date not much work has been done to develope a micro-mechanics based simplified mathematical model of fiber reinforced composites that can quantitatively explain the increase of the fracture toughness and strength of a composite with volume fraction, length and diameter of fibers, used for strengthening the composite, this is what is attempted in this paper.     

Wear of PEEK composites related to their mechanical performances

A series of polyetheretherketone-based composites was investigated, blended with different contents of polytetrafluoroethylene and/or graphite, and reinforced with various amounts of short carbon fibres. The mixture of the PEEK with various fillers was achieved by twin-screw-extruders. Thereafter, the composites were finally manufactured using an injection moulding machine. Testing of the tribological properties of the PEEK composites was carried out on a block-on-ring apparatus. The dependence of mechanical properties, e.g. Charpy impact resistance, fracture toughness, flexural modulus and strength, on various filler contents of these composites was also investigated, which is believed to be of help towards a better understanding of the steps on how to improve the composite’s wear resistance.     

Layer-Graded Cu/B4C/Graphite Hybrid Composites: Processing,Characterization, and Evaluation of Their Mechanical and Wear Behavior

In this article, we synthesized and studied functionally graded multilayered Cu/B₄C/graphite hybrid composites. Two classes of layer-graded composites were considered: pure Cu layer with two layers consisting of different particle sizes and uniform particle volume and a pure Cu layer with a single additional layer. The properties of the layer-graded composites were compared to those of single layer composites of two different particle sizes (1–20 µm and 60–90 µm). The composites were tested for compression strength, flexural strength, hardness, density, and wear and braking performance at a range of sliding speed conditions (5, 10, 30, and 35 m/s). The microstructure of the interfaces in the layer-graded composites was characterized to determine the quality of bonding. We found that the layer-graded composites possess improved compression and flexural strength due to lower porosity and residual compressive stress in the composite layer aided by the work-hardening of the Cu layer. The presence of the ductile Cu layer improves the toughness and crack resistance properties of layer-graded composites by macrostructure toughening mechanism. The layer-graded composites possess improved wear resistance and braking performance at both low and high sliding speed conditions due to reduced third-body wear, oxidation, and softening of composites, aided by effective heat conduction through the Cu layer. Finally, the wear mechanisms operating at various speeds were discussed with the help of microscopic and X ray diffraction studies.     

Wear behaviour of Al/(Al2O3p+SiCp) hybrid composites

In this study, dry sliding metal–metal and metal–abrasive wear behaviours of the aluminium matrix hybrid composites produced by pressure infiltration technique were investigated. These composites were reinforced with 37 vol% Al₂O₃ and 25 vol% SiC particles and contained up to 8 wt% Mg in their matrixes. While matrix hardness and compression strength increased, amount of porosity and impact toughness decreased with increasing Mg content of the matrix. Metal–metal and metal–abrasive wear tests revealed that wear resistance of the composites increased with increasing Mg addition. On the other hand, abrasive resistance decreased with increasing test temperature, especially above 200 °C.     

Tribological behaviour of Si3N4 and Si3N4-%TiN based composites and multi-layer laminates

Si₃N₄-TiN based multi-layer laminates exhibit differences in residual stress between individual layers due to a variation of the thermal expansion coefficient between the layers. The residual stress distribution in these multi-layer laminates is known to improve the apparent macroscopic fracture toughness. In this work, the tribological behaviour of bulk, composites and multi-layers laminates are investigated. Si₃N₄ bulk, Si₃N₄ based composites with 10, 20 and 30 wt% TiN and different multi-layer laminates have been tested under dry conditions with reciprocal movement using a ball-on-block configuration. In particular, the influence of sliding directions with respect to the layer orientations has been investigated.The experimental results show that wear resistance increased with increasing TiN content in Si₃N₄-TiN composites. However, multi-layer laminates exhibit an up to three times higher apparent fracture toughness, but do not show an improvement of wear resistance compared to composites.     

Role of Nano-YbF3-Treated Carbon Fabric on Improving Abrasive Wear Performance of Polyetherimide Composites

A method for surface treatment of carbon fabric with nano-particles of rare earth salt (ytterbium fluoride–YbF₃) was tried first time in the authors’ laboratory to enhance the fiber–matrix interface, and has been reported here. In this article authors have reported on the performance evaluation of composites developed from the four fabrics treated with various doses viz. 0, 0.1, 0.3, and 0.5 wt% of YbF₃. The abrasive wear performance of these composites was evaluated by abrading the composites against silicon carbide abrasive paper under varying loads. The treated fabric composites exhibited lower coefficient of friction and higher wear resistance as compared with untreated fabric composite. A linear correlation between ILSS (interlaminar shear strength) and wear resistance was observed. Both were the highest for 0.3% dosing of fabric. Since it was also desirable to compare the efficiency of this novel method of treatment of carbon fibers with conventional one, a few results of composites with plasma-treated carbon fabric were compared with the nano-particle-treated fabric composites. It was concluded that the latest method improved the abrasive wear resistance of composites almost two times more than the plasma-treated composites. Fiber–matrix interface was strengthened because of the treatment as observed from SEM studies, ILSS, and matrix pick-up studies. Increased roughness of fiber surface was observed in topographical analysis by SEM. Effect of treatment on fiber was also observed by adhesion test and fiber tow tension test. SEM studies of worn surfaces were performed to understand wear mechanisms.     

玻璃纤维/PC树脂/LY12铝合金叠层复合材料界面处理及其性能

采用热压固化成型工艺,成功制备了玻璃纤维／PC树脂／铝合金叠层复合材料,并对该材料的界面结合状况与性能进行了分析。结果表明：通过对铝合金表面进行喷丸和酸腐蚀综合处理及对玻璃纤维进行0．5％硅烷偶联剂水溶液涂层处理,叠层复合材料各界面的结合状况良好;抗拉强度达到210．2MPa,抗弯强度达到325MPa,冲击韧度大于173．5kJ／m^2,其阻尼性能尤其突出,自由衰减率达到0．332,可与粘弹性阻尼材料媲美。     

影响纳米陶瓷刀具材料力学性能的主要因素

纳米复相陶瓷材料具有较高的抗弯强度和断裂韧性，可以作为高性能的刀具材料，其增韧补强机制主要源于基体晶粒的细化及由沿晶断裂向穿晶断裂模式的转变，同时热处理对微裂纹的愈合作用也不可忽视。文中根据其强韧化机理并结合实验研究，对研制高性能纳米陶瓷刀具材料需考虑的主要因素进行了探讨。     

SiCp/Cu复合材料的显微组织和力学性能

采用非均相沉淀包裹法制得铜包SiC复合粉体,利用热压烧结工艺制备了含有体积分数为20%～65%SiC颗粒的SiCp/Cu复合材料.用X射线衍射仪、扫描电镜、能谱分析等测试方法对试样进行了成分和微观形貌分析.结果表明:包裹法制得的SiCp/Cu复合材料中基体铜形成连续的结构,SiC分散较均匀;随着SiC含量的增加,试样孔隙率提高,抗弯强度下降;而硬度则先增后降,并在SiC体积分数为35%时出现最大值;所有试样均表现为脆性断裂.     

Investigations on mechanical and structural aspects of ultrasonic hybrid polymer mixture welding for industrial applications

Two-dimensional C_f/Al composites were fabricated by liquid-solid extrusion following vacuum infiltration technique (LSEVI), and defects were studied and analyzed through optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope(TEM), and the tests of ultimate tensile strength (UTS). Through research, it was found that gas impurities were the main factors to generate hole defects within the 2D-C_f/Al composites, so vacuum level of the test system should be higher than 0.09 MPa. The infiltration of composites would not be sufficient and uniform under the low squeeze pressure of 50 MPa and low squeeze temperature of 590 °C. However, when squeeze pressure was larger than 90 MPa, fiber damage appeared, and macro internal cracks even occurred if it was over 100 MPa. Poor tensile behavior of composites between carbon fibers and matrix might arise because of the inappropriate process parameters. Brittle tensile fracture of composites was observed under the higher preform preheating temperature of 640 °C, and Al₄C₃ was found. Separated fibers and aluminum alloy of tensile fracture might occur under the lower preheating temperature of 580 °C. These defects hindered the improvement of property of C_f/Al composites greatly, and they should be avoided. Through contrast of UTS, internal cracks and poor tensile behavior were the most detrimental factors. Their UTSs were 45 and 117 MPa, respectively, which were less than 120 MPa of matrix. Improved process parameters were used to prepare the 2D-C_f/Al composite, and its defects were seldom found, so UTS of composite was improved 93.3 % than that of matrix.     

短切碳纤维含量对WC-TaC复合陶瓷刀具材料微观组织及力学性能的影响

采用真空热压烧结技术,以Ni为粘结相,短切碳纤维(C_(sf))为增强相,在1550℃下制备了不同C_(sf)含量的WC-Ta C-C_(sf)复合陶瓷刀具材料。研究了C_(sf)含量对WC-Ta C-C_(sf)复合陶瓷刀具材料微观组织和力学性能的影响,结果表明:复合材料中加入一定含量的C_(sf)可以显著细化晶粒。随着C_(sf)含量的增加,硬度逐渐减小,抗弯强度和断裂韧度先增大后减小,当C_(sf)含量为1.5wt%时,材料的综合力学性能最好,硬度、抗弯强度和断裂韧度值分别为12.79+0.28GPa、1072.71+22MPa和14.45+0.2MPa·m~(1/2)。     

Effect of reinforcement on wear behaviour of aluminium hybrid composites

Abstract

Aluminium metal matrix composites are among the recent developments in engineering applications to meet the present day need of light weight, high strength/weight ratio and good wear properties. In the present study, AlSi10Mg alloy reinforced with 3, 6 and 9 wt-% alumina with constant 3 wt-% graphite particles was produced by stir casting technique. Microstructural investigations as well as evaluation of mechanical properties such as hardness, tensile strength and double shear strength were conducted on composites and unreinforced alloy specimens. Tribological behaviour of hybrid composites was studied using pin on disc test machine. Wornout surfaces were analysed using scanning electron microscopy, and wear debris were analysed using X-ray diffraction. Results revealed that the mechanical properties of hybrid composites were higher than unreinforced alloy. Dry sliding wear test results indicated that the aluminium alloy reinforced with 9 wt-% alumina and 3 wt-% graphite has highest wear resistance compared to unreinforced alloy.     

Influence of fiber parameters on tensile, flexural, and impact properties of nonwoven coir�Cpolyester composites

The tensile, flexural, and impact properties of coir fiber/polyester composites were evaluated. The untreated green husk coir fibers with different proportion in length and content were used as reinforcements in polyester polymer-based matrices. The mathematical models of tensile, flexural, and impact properties were developed and optimized using statistical package to find the optimum fiber parameters for maximum mechanical properties. The results are shown that the fiber content in weight percentage is playing major role than the fiber length on the improvement of tensile, flexural, and impact strength properties.