Materials Science Forum Vol. 813

Abstract: In this paper, compression performance of composite stiffened panels after bolted repair and scarfed bonded repair is presented. Several tests have been performed on the four kinds of stiffened panels. All the experiments show the influences of different damage actions, different repair methods for the mechanical properties of stiffened panels are different. Furthermore, numerical finite element models have been developed and solved using the software ABAQUS. In addition, stiffener-skin debonding was considered in the finite element models in order to ensure a better consistence with the fact. The comparison of simulation results and experiment shows that the finite element modeling method is effective. The result suggests that the failure load and the stiffness of the repaired stiffened panel are recovered close to the virgin ones’.

Abstract: The dynamic response of a floating structure subjected to underwater explosion is greatly complicated by the explosion of a high explosive, propagation of shock wave, complex fluid–structure interaction phenomena, and the dynamic behavior of the floating structures. A numerical investigation has been carried out to examine the behavior of stiffened steel plates subjected to shock loads resulting from an Underwater Explosion (UNDEX). The aim of this work is to obtain the optimal configuration to resist underwater shock loading. A non-linear dynamic numerical analysis of the underwater explosion phenomena associated with different geometrical stiffened steel plates is performed using the ABAQUS/Explicit finite element program. Special emphasis is focused on the evolution of mid-point displacements. Further investigations have been performed to study the effect of including material damping and the rate-dependant material properties at different shock loads. The results indicate that stiffener configurations and shock loads affect greatly the overall performance of steel plates and sensitive to the material data.

Abstract: To investigate ocean environmental effects of salt water and xenon light, salt water spray test and xenon test were performed on long immersion hours. CFRP (Carbon Fiber Reinforced Polymer) specimens were prepared for salt water spray experiment, xenon light exposure experiment and mechanical tensile tests. The composite specimens with total 15 layers were manufactured with diverse fiber orientations of [0°]_15, [90°]₁₅ and [0°₃/+45°₂/-45°₂/90°/-45°₂/+45°₂/0°₃]. After applying environmental conditions, the tensile strength was compared with the tensile strength without environmental conditions. The influence of different fiber orientation was also investigated, respectively. Finally, the results showed that the tensile strength of composite specimens was affected by salt water and xenon light clearly.

Abstract: With the process optimizing, electromagnetic performance designing, structural strength/stiffness checking and testing, a cost-effective and environment-friendly approach to manufacturing a submarine radome and its related products at low cost is introduced in this article: The submarine radome is made of an epoxy-matrix composite reinforced with E-glass fabric through the vacuum infusion and heating cure processing.

Abstract: Using experimental study, major emphasis of the present study is to determine the influence of reinforcement ratio on structural behavior of the prestressed beams made of UHPCC in terms of first crack load, peak load, ductility, and load-deflection characteristics. A UHPCC mixing proportion was presented firstly. 8 rectangular beams of size 100x300x3000mm made of UHPCC were designed, fabricated and tested in this investigation. Influence of reinforcement ratio of load bearing capacity, deflection and crack pattern of beams were performed and analyzed. Based on experimental results, some conclusions were drawn.

Abstract: Effects of curing temperature on glass fiber/urethane composite’s mechanical and thermal properties were investigated in this paper. L100 and curing agent C3 were mixed sufficiently with the mass ratio of 100:15 at the temperature of about 50°C, and 3 layers of glass fibers with the size of 10cm×30cm (the thickness of each layer is 0.2mm) were prepared. Then glass fabric/L100 polyurethane composites were fabricated by vacuum-assisted hand lay-up process at the temperature of 150°C, 160°C and 170°C, respectively. As the resin system is used in pultrusion process which demands the resin system can cure adequately within 5min to 15 min. The isothermal differential scanning calorimetry (DSC) method was used to investigate the curing time at the above three temperatures to testify whether the resin system can cure during a short span of time to meet the requirement. The results demonstrate that L100/C3 resin system cures within 8-10min at the temperature of 150°C and 160°C, while under 170°C, the resin system cures fully within 5min,which clearly show that the resin system meet the basic requirement of fast process. In order to better analyze the effect of curing temperature on sample’s mechanical properties, corresponding mechanical tests were conducted. The tension tests demonstrate that the tensile strength and elongation at break reduce with the rise of curing temperature. The interface strength test and field emission scanning electron microscope photography were conducted. The results show that higher curing temperature leads to lower interface strength. The decrease of the interface strength is due to the different reactivity of three reactive groups in L100. With the rising of temperature, reactivity groups tend to react with curing agent C3, but not to combine with coupling in the surface of glass fiber, hence weakens the link between resin and fiber. This assumption can be confirmed by the DSC tests, which show that curing temperatures have little effects on glass transition temperature of the samples. Additionally, the infrared spectra of the composites cured at the above three different temperatures indicate that curing temperatures exert no significant influence on the composition of the composites. Based on the above results, 150°C is chosen to be the optimal curing temperature for the glass fabric/L100 polyurethane composites.

Abstract: In this work, carbon fibers were sized with three different sizing agents in order to improve the performances of carbon fibers and the interface of carbon fibers composites. The surface characteristic was investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), at the same time, the single fiber strengths and weibull distributions were also studied in order to understand the effect of different sizing agents on carbon fibers. The interlaminar shear strength (ILSS) of the composites was also measured to study the effect of fiber coatings on the interface of the composites. X-ray photoelectron spectroscopy (XPS) was also used to analyze the element composition of carbon fiber modified by different sizing agents. This investigation shows that different sizing agents could give a different composition of surface functional group for carbon fiber, which is crucial to the interfacial performance of carbon fiber composites.

Abstract: Composite to metal joints are gradually found in the marine industry for the attachment of lightweight components to metallic structures. The puropose of this study is to invistigate the composite sandwich to steel joint for naval ships. The main emphasis of the study was placed on the mechanical properties of a hybrid joint between a sandwich glass fibre reinforced plastic superstructure and a steel hull. Based on the experiments of a base joint, a new numerical simulation method was used to analyze the performance of the base joint and the optimized joint. The optimized joint was presented due to reducing weight and avoiding eccentric load. The numerical predictions of the base hybrid joint showed a very good correlation with the experiment results, which validated the reliability of the new numerical simulation method. The strength of the optimized hybrid joint was evaluated through static simulation. This phenomenon is similar to the base joint. But there is no additional stress concentration induced by load eccentricity and internal bending. The optimized joint has 11% lower weight than the base joint, and the stress of the optimized joint is only about 4% ~ 67% of the base one. The results of the present work imply that the change of geometry and material is an effective method to improve the performance of the composite sandwich to steel joint.

Abstract: The cores have to be spliced in the manufacturing process of sandwich plate due to the processing technology, the influence of core splice, compared with integrated core, on mechanical behavior of sandwich plate were investigated through two experiments. Two styles of specimens (B-style and C-style) were taken into experiments in sequence which included two kinds of plate with different cores.Firstly, it was found in stiffness experiment that stiffness and strength of sandwich plate with splicing core were obviously weaker than that with integrated core, which mean the former performed larger deformation under the same predetermined load with higher strain and behaved lower ultimate bearing capacity. Meanwhile the failure modes were mainly sheet crushing collapse and there was no evident difference in the failure mode of the two styles specimens with different cores. It concluded that the cores splice reduced the stiffness in location of two core splicing but the effect on the failure mode was slight.Secondly, it was found in stability experiment that the mechanical behaviour was approximately linear under the predetermined axial load and the predetermined out-of-plane load and similarly bulking strength of the sandwich plate with splicing core was about 10%~15% lower than that with integrated core. Basically, delamination between sheet and core kept accompany with bulking of the plate each time and two styles specimens with different cores didn’t show evident differences in failure mode as well. It demonstrated the conclusion and that core splice accounted to make the specimens produced geometric imperfections which resulted in stiffness reduction.Thirdly, based on experiments it was clear that the mechanical behaviour of sandwich plates with splicing cores suffered from more obvious discreteness compared with that with integrated cores, which indicated that manufacturing technology had greater influence on the former and core splice should be avoided in some important location of structure.Lastly, numerical simulation method based on progressive damage analysis was also studied and good correlation with experimental results was obtained, which could well predict the mechanical behaviour of the sandwich plates with splicing core and integrated core.

Abstract: The polyurethane matrix composites consisting of CNT and NiTi springs are prepared and the microstructure, mechanical property and damping property of the composites are investigated. It was found that the CNT and NiTi spring exhibit a good interfactial bonding with the matrix. The elastic modulus and tensile strength have been enhanced by the addition of CNT and NiTi spring. The NiTi spring is helpful to increase the recovery strain and enhance the energy absorption of the composites by the pseudoelastic deformation under the large deformation. The NiTi spring can not increase the damping property under low vibration amplitude because the pseudoelastity of the spring is not actuated when the deformation is small.