Applied Composite Materials (v.23, #5)

In this paper, the comparison of fatigue life between C/SiC and SiC/SiC ceramic-matrix composites (CMCs) at room and elevated temperatures has been investigated. An effective coefficient of the fiber volume fraction along the loading direction (ECFL) was introduced to describe the fiber architecture of preforms. Under cyclic fatigue loading, the fibers broken fraction was determined by combining the interface wear model and fibers statistical failure model at room temperature, and interface/fibers oxidation model, interface wear model and fibers statistical failure model at elevated temperatures in the oxidative environments. When the broken fibers fraction approaches to the critical value, the composites fatigue fracture. The fatigue life S–N curves and fatigue limits of cross-ply, 2D and 3D C/SiC and SiC/SiC composites at room temperature, 550 °C in air, 750 °C in dry and humid condition, 800 °C in air, 1000 °C in argon and air, 1100 °C, 1300 °C and 1500 °C in vacuum, have been predicted. At room temperature, the fatigue limit of 2D C/SiC composite with ECFL of 20 % lies between 0.78 and 0.8 tensile strength; and the fatigue limit of 2D SiC/SiC composite with ECFL of 20 % lies between 0.75 and 0.85 tensile strength. The fatigue limit of 2D C/SiC composite increases to 0.83 tensile strength with ECFL increasing from 20 to 22.5 %, and the fatigue limit of 3D C/SiC composite is 0.85 tensile strength with ECFL of 37 %. The fatigue performance of 2D SiC/SiC composite is better than that of 2D C/SiC composite at elevated temperatures in oxidative environment.
Keywords: Ceramic-matrix composites (CMCs); Fatigue; S−N curve; Life prediction

Impact Response Study on Covering Cap of Aircraft Big-Size Integral Fuel Tank by Fusheng Wang; Senqing Jia; Yi Wang; Zhufeng Yue (953-972).
In order to assess various design concepts and choose a kind of covering cap design scheme which can meet the requirements of airworthiness standard and ensure the safety of fuel tank. Using finite element software ANSYS/LS- DYNA, the impact process of covering cap of aircraft fuel tank by projectile were simulated, in which dynamical characteristics of simple single covering cap and gland double-layer covering cap impacted by titanium alloy projectile and rubber projectile were studied, as well as factor effects on simple single covering cap and gland double-layer covering cap under impact region, impact angle and impact energy were also studied. Though the comparison of critical damage velocity and element deleted number of the covering caps, it shows that the external covering cap has a good protection effect on internal covering cap. The regions close to boundary are vulnerable to appear impact damage with titanium alloy projectile while the regions close to center is vulnerable to occur damage with rubber projectile. Equivalent strain in covering cap is very little when impact angle is less than 15°. Element deleted number in covering cap reaches the maximum when impact angle is between 60°and 65°by titanium alloy projectile. While the bigger the impact angle and the more serious damage of the covering cap will be when rubber projectile impact composite covering cap. The energy needed for occurring damage on external covering cap and internal covering cap is less than and higher than that when single covering cap occur damage, respectively. The energy needed for complete breakdown of double-layer covering cap is much higher than that of single covering cap.
Keywords: Aircraft fuel tank; Covering cap; Composite material; Impact position; Impact angle; Impact energy

Edge Delamination and Residual Properties of Drilled Carbon Fiber Composites with and without Short-Aramid-Fiber Interleaf by Zhi Sun; Xiaozhi Hu; Shanshan Shi; Xu Guo; Yupeng Zhang; Haoran Chen (973-985).
Edge delamination is frequently observed in carbon fiber reinforced plastic (CFRP) laminates after machining, due to the low fracture toughness of the resin interfaces between carbon fiber plies. In this study, the effects of incorporating tough aramid fibers into the brittle CFRP system are quantified by measuring the residual properties of bolted CFRP. By adding short-aramid-fiber interleaves in CFRP laminates, the residual tensile strength have been substantially increased by 14 % for twill-weave laminates and 45 % for unidirectional laminates respectively. Moreover, tensile failure was observed as the major mode of toughened laminates, in contrast to shear failure of plain laminates. The qualitative FEM results agreed well with the experimental results that edge delamination would cause relatively higher shear stress and therefore alter the failure mode from tensile failure to shear failure.
Keywords: Carbon fiber reinforced plastic; Aramid fiber; Interface; Fiber bridging; Machining

A polymer fabric reinforced composite is a high performance material, which combines strength of the fibres with the flexibility and ductility of the matrix. For a better drapeability, the tows of fibres are interleaved, resulting the woven fabric, used as reinforcement. The complex geometric shape of the fabric is of paramount importance in establishing the deformability of the textile reinforced composite laminates. In this paper, an approach based on Classical Lamination Theory (CLT), combined with Finite Element Methods (FEM), using Failure Analysis and Internal Load Redistribution, is utilised, in order to compare the behaviour of the material under specific loads. The main goal is to analyse the deformability of certain types of textile reinforced composite laminates, using carbon fibre satin as reinforcement and epoxy resin as matrix. This is accomplished by studying the variation of the in-plane strains, given the fluctuation of several geometric parameters, namely the width of the reinforcing tow, the gap between two consecutive tows, the angle of laminae in a multi-layered configuration and the tows fibre volume fraction.
Keywords: Satin; Textile composites; In-plane strains; Repetitive unit cell; RUC

Strength Analysis and Process Simulation of Subway Contact Rail Support Bracket of Composite Materials by Boris N. Fedulov; Alexander A. Safonov; Ivan V. Sergeichev; Andrey E. Ushakov; Yuri G. Klenin; Irina V. Makarenko (999-1013).
An application of composites for construction of subway brackets is a very effective approach to extend their lifetime. However, this approach involves the necessity to prevent process-induced distortions of the bracket due to thermal deformation and chemical shrinkage. At present study, a process simulation has been carried out to support the design of the production tooling. The simulation was based on the application of viscoelastic model for the resin. Simulation results were verified by comparison with results of manufacturing experiments. To optimize the bracket structure the strength analysis was carried out as well.
Keywords: Composite materials; Composites analysis; Design; Composite mechanics; Composites design; Mechanics of composite materials; Contact rail support bracket; Subway

Effect of Ductile Agents on the Dynamic Behavior of SiC3D Network Composites by Jingbo Zhu; Yangwei Wang; Fuchi Wang; Qunbo Fan (1015-1026).
Co-continuous SiC ceramic composites using pure aluminum, epoxy, and polyurethane (PU) as ductile agents were developed. The dynamic mechanical behavior and failure mechanisms were investigated experimentally using the split Hopkinson pressure bar (SHPB) method and computationally by finite element (FE) simulations. The results show that the SiC3D/Al composite has the best overall performance in comparison with SiC3D/epoxy and SiC3D/PU composites. FE simulations are generally consistent with experimental data. These simulations provide valuable help in predicting mechanical strength and in interpreting the experimental results and failure mechanisms. They may be combined with micrographs for fracture characterizations of the composites. We found that interactions between the SiC phase and ductile agents under dynamic compression in the SHPB method are complex, and that interfacial condition is an important parameter that determines the mechanical response of SiC3D composites with a characteristic interlocking structure during dynamic compression. However, the effect of the mechanical properties of ductile agents on dynamic behavior of the composites is a second consideration in the production of the composites.
Keywords: SiC3D composites; Ductile agents; Dynamic compaction; Finite element analysis

Prediction of Process-Induced Distortions in L-Shaped Composite Profiles Using Path-Dependent Constitutive Law by Anxin Ding; Shuxin Li; Jihui Wang; Aiqing Ni; Liangliang Sun; Lei Chang (1027-1045).
In this paper, the corner spring-in angles of AS4/8552 L-shaped composite profiles with different thicknesses are predicted using path-dependent constitutive law with the consideration of material properties variation due to phase change during curing. The prediction accuracy mainly depends on the properties in the rubbery and glassy states obtained by homogenization method rather than experimental measurements. Both analytical and finite element (FE) homogenization methods are applied to predict the overall properties of AS4/8552 composite. The effect of fiber volume fraction on the properties is investigated for both rubbery and glassy states using both methods. And the predicted results are compared with experimental measurements for the glassy state. Good agreement is achieved between the predicted results and available experimental data, showing the reliability of the homogenization method. Furthermore, the corner spring-in angles of L-shaped composite profiles are measured experimentally and the reliability of path-dependent constitutive law is validated as well as the properties prediction by FE homogenization method.
Keywords: Cure behaviour; Residual stress; Finite element analysis (FEA); Tool-part interaction

Optimization of the Temperature-Time Curve for the Curing Process of Thermoset Matrix Composites by Dragan Aleksendrić; Pierpaolo Carlone; Velimir Ćirović (1047-1063).
An intelligent optimization model aiming at off-line or pre-series optimization of the thermal curing cycle of polymer matrix composites is proposed and discussed. The computational procedure is based on the coupling of a finite element thermochemical process model, dynamic artificial neural networks and genetic algorithms. Objective of the optimization routine is the maximization of the composite degree of cure by the definition of the autoclave temperature. Obtained outcomes evidenced the capability of the method as well as its efficiency with respect to hard computing or experimental procedures.
Keywords: Optimization; Curing process; Artificial neural network; Genetic algorithm

Optimization of Resin Infusion Processing for Composite Pipe Key-Part and K/T Type Joints Using Vacuum-Assisted Resin Transfer Molding by Changchun Wang; Guanghui Bai; Guangquan Yue; Zhuxi Wang; Jin Li; Boming Zhang (1065-1078).
In present study, the optimization injection processes for manufacturing the composite pipe key-part and K/T type joints in vacuum-assisted resin transfer molding (VARTM) were determined by estimating the filling time and flow front shape of four kinds of injection methods. Validity of the determined process was proved with the results of a scaling-down composite pipe key-part containing of the carbon fiber four axial fabrics and a steel core with a complex surface. In addition, an expanded-size composite pipe part was also produced to further estimate the effective of the determined injection process. Moreover, the resin injection method for producing the K/T type joints via VARTM was also optimized with the simulation method, and then manufactured on a special integrated mould by the determined injection process. The flow front pattern and filling time of the experiments show good agreement with that from simulation. Cross-section images of the cured composite pipe and K/T type joints parts prove the validity of the optimized injection process, which verify the efficiency of simulation method in obtaining a suitable injection process of VARTM.
Keywords: Composite pipe key-part; K/T type joints; Resin infusion; VARTM; Simulation method

Analysis of Residual Performance of UD-CMC in Oxidation Atmosphere Based on a Notch-like Oxidation Model by Zhigang Sun; Hongyan Shao; Xihui Chen; Yingdong Song (1079-1098).
Experimental observation indicates unidirectional ceramic matrix composites (UD-CMC) will react with oxygen under high-temperature atmosphere inhomogeneous. As a result of the oxidation on fiber surface, fiber shows a notch-like morphology. Stress concentration near by the fiber notch causes a decline of the mechanic performance of UD-CMC. In this paper, the change rule of fiber notch depth is fitted by circular function. Based on this formula the residual strength and modulus of UD-CMC under 400–900 °C atmosphere are derived. The mechanical performance of unidirectional C/SiC composite is simulated by finite element method. The stress distribution of fiber, matrix and interface are obtained. The residual properties of unidirectional C/SiC composite are predicted by theoretical method and finite element method. And the predicting results are compared with the experiment data. The predicting results show a good accordance with experiment data, which means the notch-like oxidation model can analyze the mechanic performance of UD-CMC efficiently.
Keywords: A. Ceramic-matrix composites (CMCs); B. Mechanical properties; C. Analytical modelling; C. Finite element analysis (FEA)