Evaluation of woven fabric composites for automotive applications

This paper summarizes the results of a recent study [1] funded by the National Science Foundation to investigate the feasibility of woven fabric composite materials for automotive applications. By identifying the advantages and limitations associated with woven fabric composites and by comparison with current automotive materials, the potential for successful application of these materials is investigated. In particular, strength, fatigue, moldability, and cost effectiveness have been identified as critical indicators of the potential for these materials in automotive applications. The results of an experimental evaluation of the static and fatigue properties of woven composites and comparable unidirectional tape composite laminates are discussed. An analytic model designed to quantify the effect of fabric weave configuration on relative conformability to complex geometries is also presented. Preliminary component designs utilizing woven fabric composites are considered in terms of potential weight savings, potential fabrication methods, and projected cost effectiveness. Finally, the key factors impeding the successful implementation of these materials in particular automotive structural applications are identified and reviewed.     

Strengthening of C/SiC Composites by Electrophoretic Deposition of CNTs on a SiC Coating

The current study reports the enhancement of mechanical properties of carbon fiber-reinforced silicon carbide ceramic matrix composites (C/SiC CMCs) by the application of a carbon nanotube/silicon carbide (CNT/SiC) coating. CNTs were deposited on the surfaces of C/SiC composites using electrophoretic deposition (EPD), after which infiltration by SiC was achieved through a chemical vapor infiltration process. An EPD duration of 5 min was associated with a 40% increase in the ultimate flexural strength relative to that of composites with a pure SiC coating. The observed enhancement was rationalized by the microstructural observations of SiC infiltration into the porous CNT morphology and the subsequent formation of CNT/SiC layers on the surfaces of the composites and by the inherent toughness of the SiC whiskers. The flexural strength decreased with EPD durations greater than 5 min due to the formation of thick CNT meshes, which decreased the open porosity and thereby obstructed further SiC infiltration. This is a viable methodology for the improvement of mechanical properties of CMCs by the introduction of a ceramic coating containing CNT.     

Designing the microstructure of squeeze-cast Al composites

Retaining their high strength and stiffness up to 350°C, SiC fiber-reinforced aluminum composites are lightweight alternatives to titanium or steel parts. By combining filament winding and squeeze-casting, components of fairly complex shapes can be produced. Both Nicalon and Tyranno “hybrid” SiC fibers (that is, continuous fibers with SiC particles distributed between the fibers) were used to reinforce pure aluminum and alloy 357 matrices. Their longitudinal properties appear much more dependent on alloying elements and processing conditions than on fiber types, but hybridization is effective in raising transverse properties significantly. Failure modes can be related to microstructural features, including interfaces, fiber-to-fiber contacts, second-phase bridges between fibers and fiber damage through processing. Provided some basic rules for microstructural design are followed for the manufacture of actual parts, squeeze-cast SiC fiber aluminum composites offer great potential for defense and aerospace applications.     

Intermittent grinding of ceramic matrix composites (CMCs) utilizing a developed segmented wheel

Ceramic matrix composites (CMCs) are relatively new and promising materials for many high-technology engineering applications in harsh and severe environments due to their superior properties. Despite being mostly at the development phase, CMCs have some very successful applications in several high technology fields. However, in spite of all advantages, the employment of CMCs has been impeded by their high machining and finishing costs. Many recently developed CMCs are very difficult to machine with conventional machining technology, and improvement of the existing machining process is required and crucial. The main objectives for overcoming these technological constraints are reducing high grinding forces and tool wear, improving surface integrity and increasing material removal rate. To overcome the existing technological constraints in the grinding of CMCs, a specially designed segmented wheel has been developed. Reducing the static cutting edges via segmenting the wheel, which automatically leads to reduction of momentarily engaging cutting edges, results in a reduction of rubbing and plowing regimes. Consequently, the specific grinding energy decreases. Experimental results illustrate the high performance of the presented method. A significant reduction in normal and tangential grinding forces and an increase in G-ratio have been achieved.     

Thermal shock fatigue behavior of TiC/Al2O3 composite ceramics

The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt. % TiC/Al2O3 composites were studied. The effect of TiC and Al2O3 starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference (ΔT) and number of thermal cycles (N) on fatigue crack growth (Δα). The mechanical properties and thermal fatigue resistance of TiC/Al2O3 composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al2O3 composites is due to a "true" cycling effect (thermal fatigue). Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites.     

Fatigue and fracture toughness of epoxy nanocomposites

The fatigue and failure mechanisms of epoxy composites have been researched extensively because of their commercial importance in fields demanding materials with high specific strength. Particulate, sheets, short and long fibers with dimensions in the micrometer and nanometer range are the major fillers which have been studied for enhancing the fatigue resistance of epoxies. The nano and micro scale dimensions of the fillers give rise to unexpected and fascinating mechanical properties, often superior to the matrix including fracture toughness and fatigue crack propagation resistance. Such properties are dependent on each other (e.g., the fatigue properties of the polymer composites have been found to be strongly influenced by its toughness). This article is a review of the various developments in this field and the underlying mechanisms which are responsible for performance improvements in such composites.     

TA15钛合金焊接接头性能与断裂行为研究

对TA15钛合金氩弧焊和电子束焊焊接接头的性能与微观组织进行了分析研究,并结合断口观察,对其断裂行为进行了研究.结果表明,两种焊接接头强度均与母材相当,而塑性明显降低.焊接接头热影响区组织均呈现从粗大等轴组织到魏氏组织的过渡变化特征.疲劳断裂位置一般位于靠近熔合线的焊缝区域,主要原因是此区域存在组织突变和熔合线气孔.焊接气孔对接头疲劳性能影响较大.两种焊接接头疲劳断口特征存在明显区别.     

界面性能对单向碳纤维/环氧复合材料弯曲疲劳性能的影响

研究了界面改性对单向碳纤维增强复合材料疲劳性能的影响。通过以碳酸氢氨为电解质的阳极氧化和以马来酸酐为溶质进行的低温等离子体处理对碳纤维表面进行改性，观察交变载荷下复合材料界面性能退化和疲劳损伤规律。发现良好的界面粘接可以提高复合材料的抗疲劳性能，但是过强的界面粘接反而导致复合材料疲劳性能的下降。只有当材料具有合适强弱的界面时，才具有较好的疲劳性能。     

The high-temperature application of ceramic-matrix composites

Although much research is still required in order to develop reliable and cost-effective ceramic-matrix composites (CMCs), these materials have made great strides toward high-temperature applications. This article examines various CMCs and their high-temperature applications in both aerospace and nonaerospace fields. In the former, performance is the foremost consideration; in the latter, cost effectiveness is the prime consideration.     

Thermal shock fatigue behavior of TiC/Al2O3 composite ceramics

The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt.% TiC/Al₂O₃ composites were studied. The effect of TiC and Al₂O₃ starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference (ΔT) and number of thermal cycles (N) on fatigue crack growth (Δa). The mechanical properties and thermal fatigue resistance of TiC/Al₂O₃ composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al₂O₃ composites is due to a “true” cycling effect (thermal fatigue). Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites.     

Recent progress in ceramic matrix composites reinforced with graphene nanoplatelets

Graphene nanoplatelets(GNPs) are considered to be one of the most promising new reinforcements due to their unique two-dimensional structure and remarkable mechanical properties. In addition, their impressive electrical and thermal properties make them attractive fillers for producing multifunctional ceramics with a wide range of applications. This paper reviews the current status of the research and development of graphene-reinforced ceramic matrix composite(CMC) materials. Firstly, we focused on the processing methods for effective dispersion of GNPs throughout ceramic matrices and the reduction of the porosity of CMC products. Then, the microstructure and mechanical properties are provided, together with an emphasis on the possible toughening mechanisms that may operate. Additionally, the unique functional properties endowed by GNPs, such as enhanced electrical/thermal conductivity, are discussed, with a comprehensive comparison in different ceramic matrices as oxide and nonoxide composites. Finally, the prospects and problems needed to be solved in GNPs-reinforced CMCs are discussed.     

Investigation of residual stress effects in an alloy reinforced ceramic/metal composite

This study aims at investigating the thermal expansion behavior and internal residual strains in metal reinforced ceramic matrix composites (CMCs). A variety of Al₂O₃/A356 CMCs composites with an interpenetrating network structure and varying metal content, ranging from 10 to 40 vol.%, were produced using the pressure infiltration technique of Squeeze casting. Values of coefficients of thermal expansion (CTEs) were found to vary significantly with temperature, indicating an influence of the flow characteristics of the metal. Comparisons are made with well known methods for predicting CTEs values of metal/ceramic composites. The overall strain was found to increase with temperature and scaled proportionally with the metal content of the composite. Comparisons were also made with non-infiltrated porous ceramic preforms and a pure metallic sample. The uniform heating and cooling curves for the composite samples were found to exhibit hysterisis. Residual stress analysis and failure simulation were performed based on thermomechanics and the finite element method (FEM). This analysis is often utilized for the analysis of stress distribution or deformation of a structure. High angle X-ray and CTEs mismatch equation analysis were utilized to analyze the residual stresses at the ceramic/metal interface of the Al₂O₃/A356 composites. The relationship of residual stresses and the contact area of the ceramic/metal interface are also discussed.     

Friction and wear properties of ultra-high molecular mass polyethylene reinforced with Al2O3 nano-particle

The ultra-high molecular mass polyethylene (UHMMPE) as an artificial joint acetabular material was filled with nano-powder of Al2O3 of various mass fractions. The effect of Al2O3 mass fraction on the hardness, wetting property and tribological properties of the Al2O3-UHMMPE composites under dry friction sliding against both stainless steel and Ti-6Al-4V alloy was investigated. The morphologies of the worn surfaces of composites were observed with optical microscope. The results show that, wetting property and wear resistance of the composites are improved by filling Al2O3, while the friction coefficient is decreased largely under dry friction as compared with that of the unfilled UHMMPE. This is attributed to the reinforcing function of the nano-powder of Al2O3 in the composites. The wear of UHMMPE is dominated by plowing, plastic deformation and fatigue wear; while the Al2O3-UHMMPE composites are characterized by the mild fatigue wear.     

Effect of stress level on fatigue behavior of 2D C/C composites

Laminated carbon fiber clothes were infiltrated to prepare carbon fiber reinforced pyrolytic carbon (C/C) using isothermal chemical vapor infiltration (CVI). The bending fatigue behavior of the infiltrated C/C composites was tested under two different stress levels. The residual strength and modulus of all fatigued samples were tested to investigate the effect of maximum stress level on fatigue behavior of C/C composites. The microstructure and damage mechanism were also investigated. The results showed that the residual strength and modulus of fatigued samples were improved. High stress level is more effective to increase the modulus. And for the increase of flexural strength, high stress level is more effective only in low cycles. The fatigue loading weakens the bonding between the matrix and fiber, and then affects the damage propagation pathway, and increases the energy consumption. So the properties of C/C composites are improved.     

Testing the tensile properties of ceramic-matrix composites

This article reports the development of a mechanical testing methodology (including fixtures, extensometry, temperature control, and calibration) and procedure (including control mode options, and analysis) for ceramic-matrix composites (CMCs). Six different CMCs were tensile tested at room temperature (RT) and 1,000°C. An appreciable reduction in fracture resistance was measured for most of the systems at the high temperature, but there was little effect of an order-of-magnitude change in strain rate at either temperature. The reduced properties at 1,000°C could be essentially duplicated at RT for several of the composites by prior exposure in air at 1,000°C. The same exposure in vacuum was much less damaging; thus, oxygen would appear to be the culprit. Fractographic evidence indicated that fiber pullout in any system was a function of test temperature rather than fracture strength. Moreover, the incidence and magnitude of energy-release events during testing varied among the systems and revealed no unique connection with the state of damage induced by the prior exposures. These observations do not fit readily into any simple theoretical model. However, they do serve to identify potential limitations for this class of composite in terms of sensitivity to thermal transients in a non-inert environment.     

激光增材制造高温合金复合材料研究进展

本文对增材制造技术在高温合金复合材料中的研究进行了系统全面地梳理归纳，综述了增材制造高温合金复合材料的粉末混合、冶金过程以及强化机制，并且在增材制造高温合金复合材料显微组织、缺陷及其性能方面进行详细对比分析研究。在此基础上，分析了增材制造高温合金复合材料研究现状及进展，并且对高温合金复合材料新增强相设计、增强相添加方式及其对蠕变疲劳性能的影响机制等的研究进行了展望，本文将有利于对增材制造高温合金复合材料的研究和发展提供参考。     

CORROSION AND MECHANICAL PROPERTIES OF Ti3Al-Nb-Mo COMPOSITES FOR BIO- AND ENVIRONMENTAL MATERIALS PREPARED BY SELF-PROPAGATING HIGH TEMPERATURE REACTION

TiaAl-Nb-Mo composites were prepared by SHS using initial powder mixtures of Ti-Al-Nb-Mo and their corrosion and mechanical properties were studied to develop bio-and environmental materials. The composites reached 99.8% of theoretical densityafter the direct consolidation. The composites shows equiaxed primary α2 in a matrixof fine secondary α2 plates and ordered B2 (B0) forming a basket weave structure.The strain rate sensitivity (m = dlnσr/dlne) at 2% strain is 0.008. Corrosion po-tential and corrosion rate of the composites formed by SHS were -151.5mVSHE and5.72× 10-8A/cm2 for Ti3Al-10Nb-1.5Mo and -138.4m VSHE and 4.12×10-8cm-2 forTi3Al-12Nb-1.5Mo in a 50% NaOH-10%FeCl3 solution, respectively. Corrosion resis-tance decreased with niobium content in the composites and chloride content in theaqueous solution. Selective corrosion of α2 phase in a matrix occurred in the corrosionenvironment which suggests that the corrosion potential and rate changes are relatedto the niobium content and α2 phase in a matrix.     

硼化物颗粒增强钛基复合材料研究进展

本文综述了TiB或TiB2颗粒增强钛基复合材料的组织形貌、增强相与合金基体的界面、复合材料的力学性能等方面的研究状况。重点介绍了颗粒在铸态或热处理态的形貌,与基体的界面,合金室温强度,蠕变,疲劳等性能的研究现状。对复合材料的应用状况也进行了简单的叙述,并提出了展望。     

Fatigue crack initiation and multiplication of unnotched titanium matrix composites

Fatigue crack initiation and multiplication of the unnotched SCS-6 silicon carbide fiber-reinforced titanium matrix composites with different matrix and interfacial properties have been investigated experimentally and analytically. Ti–15V–3Al, Ti–6Al–4V, and Ti–22Al–23Nb were chosen as matrix materials. The initiation and propagation of each individual matrix crack as a function of fatigue cycles and applied stress levels were carefully monitored. The statistical distribution of crack growth rates in each composite has been constructed and analyzed. The evolution of normalized matrix crack density and stiffness reduction of these composites under fatigue loading also has been characterized. A modified shear-lag model, coupled with the strain-life equation and a fiber bridging model were used to predict the fatigue crack initiation life, matrix crack growth rate, normalized matrix crack density, and residual stiffness of the composites. The predicted fatigue properties correlated well with experimental results.