Elevated temperature off-axis fatigue behavior of an eight-harness satin woven carbon-fiber/bismaleimide laminate

The off-axis tensile fatigue behavior of a woven fiber/bismaleimide laminate is investigated at various temperatures. Emphasis was placed on characterization of the laminates and the development of an analytical fatigue damage model. Fatigue tests revealed that the material exhibits an atypical three-stage response in terms of stiffness degradation and permanent strain. Fiber yarn rotation was found to be a dominant mechanism in the initial stage of cycling causing high permanent strain and slight stiffness increase, while damage accumulation due to cyclic loading was dominant in the final stage causing rapid stiffness degradation. The mean strain variation during cycling was found to be proportional to the test temperature in each stage, and thus a more meaningful indicator for fatigue damage development. The corresponding analytical damage model was able to accurately capture the three-stage damage development. The current model can be used to determine damage development for cyclic loading at intermediate temperatures.     

Structural and elastic properties of TiN and AlN compounds: first-principles study

First-principles calculations of the lattice constants, bulk modulus, pressure derivatives of the bulk modulus and elastic constants of AlN and TiN compounds in rock-salt (B1) and wurtzite (B4) structures are presented. We have used the fullpotential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT) in the generalized gradient approximation (GGA) for the exchange-correlation functional. Moreover, the elastic properties of cubic TiN and hexagonal AlN, including elastic constants, bulk and shear moduli are determined and compared with previous experimental and theoretical data. Our results show that the structural transition at 0 K from wurtzite to rock-salt phase occurs at 10 GPa and ?26 GPa for AlN and TiN, respectively. These results are consistent with those of other studies found in the literature.     

Sparse Representations to Replace TOFD Images in Non-destructive Testing of Materials

This paper describes a proposed method for the selection of relevant samples of ultrasonic signals during automatic material inspection. Instead of the well-known time of flight diffraction (TOFD) images, data are stored as a sparse matrix in which the elements only indicate whether a defect has been detected. This technique avoids storage of useless signals received during probe displacement in cases of low and high signal-to-noise ratios that correspond to coarse-grained and fine-grained materials, respectively. The approach is based on comparing the positions of maximum amplitudes, which are randomly located when signals only consist of noise but are in the same signal range when a defect is detected. The matrix elements are then applied as inputs to a self organizing map by neural networks to produce a normalized sparse matrix as the output, with a constant number of elements. This approach will be beneficial to enable the use of selected data in intelligent systems requiring a fixed number of inputs to characterize defects.     

Experimental analysis of the strength of silver–alumina junction elaborated at solid state bonding

The mechanisms of ceramics–metal assemblies, particularly silver and alumina, can be better understood by studying the strength of their adhesion. These two materials are a priori non-reactive, their thermodynamic work of adhesion is low and the difference between their thermal coefficients of expansion in very considerable. In this study, the strength of silver–alumina junctions elaborated at solid state by thermo-compression is tested by an indirect tensile test and shearing one. The effects of several parameters such as: the pressure of bonding, the time of bonding, the temperature, and the oxygen dissolve in metal solid solution on the strength of the junction are analyzed. The obtained results show that the resistance of the junction is affected by all this parameters and it is essential to optimize these different parameters in order to increase the durability of the junction. It was also shown that the diffusion of the silver in alumina could be the cause of the damage of alumina near the interface.     

Effect of recycling on rheological and mechanical properties of poly(lactic acid)/polystyrene polymer blend

A continued increase in the use of plastics has led to an increasing amount of plastics ending up in the waste stream; and the increasing cost of landfill disposal and public interest in support of recycling has meant that plastics recycling must increase. In this work, the effect of multiple extrusion and injection of poly(lactic acid)/polystyrene polymer blend (PLA/PS) on its rheological and mechanical properties is presented. Rheological properties were studied using a capillary rheometer, apparent shear rate (γ _a), apparent shear stress (τ _a), apparent viscosity (η _a), and flow activation energy were determined. The mechanical properties of the blend were investigated on dog bone-shaped samples obtained by injection molding, tensile tests were performed, stress at break, strain at break, and Young’s modulus were determined. The results showed that the apparent viscosity of PLA/PS blend decreases monotonously with increasing the processing number. Also it was found that stress and strain at break of the blend decrease sharply after two processing cycles, whereas the processing number has a little effect on Young’s modulus.     

Comparison between double and single sided bonded composite repair with circular shape

In this study, a new approach is applied to compare the performances of single sided and double-sided symmetric composite patch with circular shape for repairing cracked aircraft structures. This is an approach that consists to evaluate the mass gain eventually obtained by the use of double symmetric composite patch if the two patch configurations give the same stress intensity factor at the crack tip. The three-dimensional finite elements method is used to compute the stress intensity factor. The obtained results show that the use of the double patch technique leads to a significant reduction of the stress intensity at the crack tip. The mass gain eventually given by the double patch technique can be very significant and this gain depends on the patch shape and the adhesive properties.     

J integral solution for semi-elliptical surface crack in high density poly-ethylene pipe under bending

The goal of this work is to analyse the severity of semi-elliptical crack defects and to study the degree of damage in the poly-ethylene pipe in bending during the crack propagation. The semi-elliptical cracks are considered in this work located in different position in the wall of the pipe. The three finite element method based on the computation of the J integral was used to analyse the fracture behaviour of these structures. The effect of the position, shape and size of the crack on the J integral values was highlighted. The effects of strain rate and the temperature on the J integral values were also examined. The obtained results show that the strain rates have a strong influence on the J integral values especially for circumferential crack at higher bending moment. However, the energy for circumferential crack is more important compared to axial crack. The effect of the depth of the crack becomes important when the ratio (a/t) reaches a critical value of 0.6 (a/t = 0.6), especially when the ratio a/c is weak (semi-elliptical crack, a/c = 0.2) where the J integral values becomes independently of the crack depth, this conclusion is opposite to the above for the poly-ethylene pipe subjected to internal pressure. We recall finally, that the temperature effect on circumferential cracks behaviour is more important compared to the axial cracks at critical crack size (a/c = 0.2 and a/t = 0.6). It is also shown that in the wall of pipe, the internal cracks are more dangerous than the external cracks.     

Hardware Simulator Design for MIMO Propagation Channel on Shipboard at 2.2 GHz

A wireless communication system can be tested either in actual conditions or with a hardware simulator reproducing actual conditions. With a hardware simulator it is possible to freely simulate a desired radio channel, making it possible to test “on table” mobile radio equipments. This paper presents new architectures for the digital block of a hardware simulator of MIMO propagation channels. This simulator can be used for LTE and WLAN IEEE 802.11ac applications, in indoor and outdoor environments. However, in this paper, specific architectures of the digital block of the simulator for shipboard environment are presented. A hardware simulator must reproduce the behavior of the radio propagation channel. Thus, a measurements campaign has been conducted to obtain the impulse responses of the shipboard channel using a channel sounder designed and realized at IETR. After the presentation of the channel sounder, the channel impulse responses are described and implemented. Then, the new architectures of the digital block of the hardware simulator, implemented on a Xilinx Virtex-IV FPGA are presented. The accuracy, the occupation on the FPGA and the latency of the architectures are analyzed.     

The effect of gamma irradiation on the microbial load,mineral concentration and sensory characteristics of liquorice (Glycyrrhiza glabra L)

Ground liquorice roots were exposed to various doses (0, 5, 10, 15 and 20 kGy) of gamma radiation from a ⁶⁰Co source. Irradiated and non‐irradiated samples were stored at room temperature. Microbial population, viscosity, concentrations of some minerals and the sensory properties of the extracts were evaluated after 0 and 12 months of storage. Tests carried out immediately after irradiation showed that the microbial count had been reduced and that the dose required to reduce the count by 1 log cycle (D₁₀) was about 2 kGy. No effect was observed on the total dissolved solids in extracts of liquorice roots. Glycyrrhizinic acid concentration in the extracts and the viscosities of suspensions produced from irradiated roots were lower than those from non‐irradiated ones. Sensory evaluation indicated that there were no significant differences (P < 0.05) in colour, taste or flavour between extracts produced from irradiated and non‐irradiated roots. However, after 12 months of storage, some mineral ion (Na⁺, Ca²⁺ and K⁺) concentrations in extracts produced from irradiated roots were lower than in those from non‐irradiated ones; no significant differences (P < 0.05) in viscosity were found between suspensions of irradiated and non‐irradiated roots. © 2002 Society of Chemical Industry