Papers by Keyword: Composite Laminate

Abstract: This paper presents mechanical properties of five layers RT800 glass mat laminate impregnated with polyester resin and subjected to three-point bending tests until break. The RT800 glass mat used as reinforcement presents randomly disposed short glass fibers with 845 g/m² specific weight. From the cured plate, twenty specimens have been cut and placed on a three-point bending device and tested using a materials testing machine with servo hydraulic command. The specimens have been carried out at Compozite Ltd Brasov and the experimental tests have been accomplished at SC INAR SA Brasov and Transilvania University of Brasov. Outstanding mechanical properties of this kind of material have been found in which the specimens have suffered delamination mainly in their median part.

Abstract: This paper presents computational matrix strain increase factors in case of parallel hexagonal shape disposed fibers in unidirectional fibers-reinforced laminae subjected to transverse loadings. Matrix strain increase factors for two shapes of disposed fibers in a unidirectional glass and HM-carbon fibers-reinforced epoxy resin lamina are given. A comparison between matrix strain increase factors in case of square shape and hexagonal shape disposed fibers for these types of laminae are also presented.

Abstract: Scarf repair parameters were optimized in this paper, to find the best repair parameter, and get better strength restoration effect. Composite laminates material was IM6/3501-6. Considering symmetry of structure, 1/4 repaired structure was taken as research object, to be built up finite element model and optimized for repair parameter. Element SOLID46 in software ANSYS was used to simulate main board and patch, element SOLID45 was used to simulate adhesive layer, to build up composite scarf repair finite element model. Because of small scarf repair angle and small ratio of adhesive layer thickness to composite laminate thickness, repair structure geometry was complex, to get exact calculation result, mesh was refined at place where stress is concentrated. There were 4488 element in the built up finite element model, with nodes number as 6263. Tsai-Wu rule and maximum shear stress was taken as failure criteria for composites laminate and adhesive layer respectively. With consideration on scarf ratio and adhesive layer thickness on repaired specimen strength, three dimension finite element models for scarf repair on composite laminates was constructed. Compared with experiment, it was found that finite element model agreed with experiment, thus validity of scarf repair model was proved. By Changing the value of each factor, finite element calculation of the repaired structure failure load showed that: the optimal value of scarf ratio is 1:20; influence of adhesive layer thickness of failure load of scarf repair structure is not obvious, generally 0.1mm meets the requirements; failure load increases when adhesive layer elastic modulus increases, but the rate of increase slows down gradually. Then the earliest failure site was analyzed according to finite element stress calculation result, failure process of adhesive layer was simulated, adhesive layer failure process was predicted, from 0 degrees to 45 degrees, and the adhesive layer top part first destroys, then spreads to 45 degrees to 90 degrees, and spreads to the adhesive layer lower end.

Abstract: The reliable detection of composite material is dramatically important with its wide application in the aerospace industry. A new post-processing mode of ultrasonic array inspection, entitled total focusing method(TFM), offers significant advantages including high sensitivity and greater inspection coverage. Based on this mode, a wave velocity correction method for the elastic anisotropic of composites is put forward. Subsequently, practical application is carried out to image and locate the defect in a composite laminate sample to demonstrate the advantage of the described method. The results show that the proposed method can effectively improve the ability to detect and evaluate defects in composite laminates.

Abstract: Development of the Korean small scale aircraft (KC-100) has been carried out by KAI (Korea Aerospace Industry Ltd.) for the BASA(Bilateral Aviation Safety Agreement) program with FAA. The KC-100 aircraft adopted the environmental friendly whole composite structure concept due to low fuel consumption owing to its light weight. However the composite structure has a disadvantage. They are very weak against impact damage due to FOD (Foreign Object Damage). This study is to investigate the residual compressive strength of the carbon/epoxy fabric and UD (Unidirectional prepreg tape) laminate due to impact damages. This residual compressive strength test follows fully the ASTM standard test procedure. Experimental investigation results reveal the residual strengths and the damage mode and size of impact damage specimens. Through these tests, it is found that the residual strength of the impact damage specimens is greatly reduced in comparison to the undamaged specimens depending on increase of both the indentation depth and the impact energy. The size and shape of damage zone greatly affects the reduction of the compressive strength.

Abstract: A major concern affecting the efficient use of carbon fibre reinforced composite laminates in the aerospace industry is the low velocity impact damage which may be introduced accidentally during manufacture, operation or maintenance of the composite structures. It is widely reported that the contact behavior of composite laminates under low-velocity impact can be obtained under quasi-static loading conditions. This paper focuses on the study of the correlation of the dent depth to the maximum contact force and damage of composite laminates under quasi-static loading. Analytical and finite element simulation approaches were employed to investigate relations between the contact force and the dent depth. Experimental investigations on the correlation between dent depth, maximum contact force and damage include quasi-static indentation testing, optical and scanning electron microscopic examination of the damage under different loading levels. The effect of damage initiation and growth on the contact behaviour has been discussed. Results show that consistent correlations between the dent depth, maximum contact force and damage exist and can be predicted with the analytical and numerical approaches. Dent depth can be used as an engineering parameter in assessing the severity of damage for composite structures that are subjected to low-velocity impact. This may lead to the development of a cost-effective technique for the inspection and maintenance of composite structures in aerospace applications.

Abstract: For designing the wheelchair structure under the seat loading, the stresses and failure indexes in each ply of the composite laminate are obtained by the finite element analysis. Using the Tsai-Wu criterion and delamination criterion, the stacking sequence [0₄/90₄/45₄/-45]_s is the final optimal design for the wheelchair frame. On the contrary, the uni-directional laminates, i.e. [90₁₃] s, [45₁₃] s and [-45₁₃] s, are bad designs.

Abstract: In this work, the residual stresses for composite laminates [0₂/θ₂]_S determined by means of the incremental hole-drilling method with a formula to express the relationship between the residual stresses and the relaxed strains around the drilled hole. Then the ageing tests related to hydrothermal condition are carried out to analyze the influence on the residual stress redistributions and also on the mechanical behaviors of the carbon/epoxy laminates.

Abstract: Thermally induced vibration (TIV) of composite laminate subjected to suddenly applied heating is studied using finite element (FE) method in this paper. Some Python programs written by the authors are used to process the data of the analysis flow, and complete the pre- and post-process of FE models used in the four analyses. An equivalent displacement method is proposed to calculate equivalent temperature load. Dynamic responses of six composite laminates with different sizes are analyzed with solid FE models and shell FE models. The results gotten by FE method are in close proximity to that gotten by classic theory and shear theory under certain conditions. It is proved that the TIV analysis method proposed in this paper is reliable and efficient. The TIV analysis with FE method based on equivalent displacement method can solve the dynamic response of a structure due to sudden changes of temperature or suddenly applied heating.

Abstract: Based on energy balance equation, the relationship between the biggest impact contact force with the pit depth in the process of impact was derived by the relationship between impact energy and indentation depth, T700S/5228 and T300/5222, two different toughness of carbon/epoxy resin composite material, are chose. The corresponding relationship between impact energy (static pressure mark force) and indentation depth was got by the contrast analysis on the low speed impact test and the static pressure mark test, and showed the similar trend with static pressure mark test of static force and indentation depth relationship. This similar trend that obvious turning points were appeared in some indentation depth showed the effectiveness that using the quasi static method to simulate the low-velocity impact of composite laminate to a certain extent.