COMPOSITES SCIENCE AND ENGINEERING

THE INFLUENCE OF CONTOUR FEATURES ON THE SURFACE FREE ENERGY OF BONDING REPAIR OF COMPOSITE MATERIALS

HE Qiang, YANG Wen-feng, YANG Xiao-qiang

2020, 0(12): 5-9.

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The relationship between surface topography and surface free energy is very important to reveal the fundamental mechanisms that govern adhesion for bonding repair of glass fibre reinforced resin matrix composites. The surfaces were created by sanding that used different items of sandpaper. The topography of the surfaces was measured using laser confocal and the contours were generated. The surface free energy was computed by measured contact angles. Feature-preserving contour filtering was carried out based on chord and angle-deviation criterion. The contour feature consisted of contour feature points, chord height distribution curve and angle-deviation distribution curve was acquired simultaneously. The relationship between contour features and surface free energy was analyzed. The results show that the contour has larger numbers of feature points, greater differences between the chord and angle-deviation distribution curve, and the corresponding surface energy will be larger which effectively supports the adhesion theory based on mechanical interlocking.

INFLUENCE OF SHORT BASALT FIBER ON CHLORIDE ION CORROSION REISTANCE OF CONCRETE

XIE Guo-liang, SHEN Xiang-dong, LIU Jin-yun, ZHANG Bin

2020, 0(12): 10-14.

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In order to study the influence of chopped basalt fiber on the corrosion resistance of concrete under the action of chloride salt freeze-thaw, five groups of concrete with different basalt fiber content were prepared in the experiment. The effects of basalt fiber content on concrete compressive strength, free chloride ion concentration and chloride ion diffusion coefficient were studied and analyzed, and a quantitative functional relationship model between chloride ion diffusion coefficient and fiber content was established. The results of the study show that the addition of basalt fiber improves the compressive strength of concrete and reduces the damage to the concrete compressive strength caused by freeze-thaw cycles. When the basalt fiber content is 1.2 kg·m^-3, the compressive strength is the most obvious. The appropriate amount of basalt fiber is beneficial to reduce the free chloride ion concentration and chloride ion diffusion coefficient in the concrete, and the large amount of basalt fiber will cause fiber agglomeration to form pores, resulting in rapid growth of free chloride ion in the early stage of concrete. Under the action of chopped basalt fiber, there is a good quadratic function relationship between the chloride ion diffusion coefficient of concrete and the content of basalt fiber.

THE OPTIMIZATION OF COMPOSITE LAMINATES CONSIDERING IN-SITU EFFECT BY ADAPTIVE GENETIC ALGORITHM

WANG Xuan, XU Nuo, ZHOU Chun-ping, DING Chang-fang

2020, 0(12): 15-20.

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The prediction of laminated composite strength was influenced by in-situ effect of the ply, further influencing the optimization of composite laminates with strength ratio as the goal. MATLAB programming and ABAQUS analysis were developed to build an optimization platform for composite laminate optimization by genetic algorithm, which include standard genetic algorithm, adaptive genetic algorithm and adaptive genetic algorithm considering the in-situ effect. An example of a laminate under unidirectional loading was performed by using the optimization platform. The results show that optimization efficiency was improved by using adaptive genetic algorithm. The results also show that not only the fitness of the individual using adaptive genetic algorithm considering in-situ effect is better, but also the laminate with optimized stacking sequence has a higher strength ratio. Thus a more accurate and reasonable optimization for composite laminates was realised.

RESEARCH ON BENDING DEFLECTION OF SANDWICH BEAM BY ENERGY METHOD

WU Xiao

2020, 0(12): 21-25.

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The shear force expression of sandwich beam section under external load is derived, and the strain energy function of sandwich beam during bending is written by using the stress expression of sandwich beam section. The strain energy function is partial to the concentration to obtain the bending deflection of sandwich beam at a concentrated force point. The results show that the energy method has a high accuracy in calculating the bending deflection, and the experimental results are in good agreement with those of related literature.

STUDY ON BENDING PROPERTY OF CRACKED STEEL PLATES REINFORCED BY CFRP PLATES

ZHANG Tong-tong, WU Jian, WANG Wei-bo

2020, 0(12): 26-30.

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For the bending steel plate with surface cracks, the reinforcement scheme is designed based on the theoretical solution of interface stress distribution of bending steel plate reinforced with composite materials. The finite element simulation was used to analyze the interface stress distribution and the bending behavior of steel plate before and after reinforcement. Finally, the reinforcement scheme and calculation method were verified by experiments. The research shows that the finite element simulation results are consistent with the experimental results. For bending steel plates with surface cracks, reinforcement by CFRP can significantly improve the bending stiffness and bearing capacity, and the reinforcement effect is significant.

COMPARISON BETWEEN THE LOAD-DISPLACEMENT CALCULATION MODEL BASED ON THE STEEL REINFORCED CONCRETE TENSION COLUMN WITH PRESTRESSED CFRP REINFORCEMENT

ZHANG Peng, ZHAO Xiao-dong, DENG Yu, SHEN Min-he

2020, 0(12): 31-37.

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In order to explore the influence factors of load displacement curve and ductility of prestressed carbon fiber reinforced steel reinforced concrete eccentric columns and accurately simulate the change trend of load displacement curve, seven prestressed carbon fiber reinforced steel reinforced concrete columns with different load eccentricity and tension level were tested in eccentric tension, and the load displacement of prestressed carbon fiber reinforced steel reinforced concrete eccentric columns was established on the basis of the test. The model is calculated and the calculated results are compared with the test results. The results show that the load eccentricity and the prestressed tension level are the important factors affecting the load displacement curve and ductility of the specimen, and the calculated value of the load displacement model is in good agreement with the test value, which shows that the model can better reflect the stress and deformation process of the prestressed carbon fiber reinforced steel reinforced concrete eccentric tension column.

RESEARCH ON ECCENTRIC COMPRESSION BEHAVIOUR OF CFRP-CONFINED CONCRETE FILLED STEEL TUBULAR COLUMNS

LI Kun-ming, CHEN Lian-meng, WU Dong-yan, ZHAO Jun-liang

2020, 0(12): 38-42.

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This paper presents the results of a recent study on the eccentric compression behaviour of carbon fiber reinforced polymer (CFRP) confined concrete filled steel tubular columns. A total of 6 specimens were prepared and tested in three pairs under different eccentricities. The length to diameter ratio of all specimens is 5. Thin steel tube with diameter to thickness ratio of 100 was adopted for all specimens. The load-strain curves, load-deflection curves were obtained from the tests. The Jiang and Teng (2012) eccentric compression column model for FRP confined reinforced concrete was modified to predict the columns of present study, the theoretical load-deflection curve of the specimens were calculated and compared with test results.

EXPERIMENTAL STUDY ON THE BOND PERFORMANCE BETWEEN BFRP BARS AND CARAL CONCRETE IN MARINE ENVIRONMENT

GAO Ao, YANG Shu-tong, GAO Guang-xi, WANG Xiu-ying

2020, 0(12): 43-53.

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Experiments were carried out to study the basic mechanical property of seawater coral concrete and the bond performance between coral concrete and BFRP bars under different marine curing environment (tidal zone immersion and seawater immersion), different bonding lengths (2.5d, 5.0d and 7.5d), different diameters (d=8 mm and d=12 mm), and different curing periods (30 d, 60 d and 90 d). The test results show that the compressive strength, axial compressive strength, flexural strength and elastic modulus of coral concrete show a trend of increase first and then decrease with the increase of the curing age, the specimens with a bond length of 2.5d and 5d fail due to the pull-out of the BFRP bars from the concrete, while the specimens with a bond length of 7.5d fail due to the split of the coral concrete or the BFRP bar. The bond-slip curve can be divided into five stages, which include micro slip stage, sliding stage, stripping stage, declining stage and residual stage. Under the same condition, the maximum average bond stress decreases with the increase of the bond length and the diameter, while the residual bond stress decreases with the increase of bond length, the maximum average bond stress in seawater zone is higher than that in tidal zone. With the growth of the curing age, the maximum average bond stress value of the specimens for diameter of 8 mm show an upward trend, and that of the specimens for diameter of 12 mm show a trend of increasing first and then decreasing. The residual bond stress in the seawater immersion environment shows a trend of increasing first and then decreasing, and it shows a trend of decreasing gradually in the seawater tidal environment.

STUDY ON THE EFFECT OF MULTI-FACTOR COOPERATION ON THE BOLTED CONNECTION STRENGTH OF GF/VE COMPOSITE MATERIALS

CAI Zheng-lin, MA Peng, LI Jin, KANG Shao-fu

2020, 0(12): 54-58.

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In this paper, glass fiber/vinyl ester (GF/VE) composite was prepared by vacuum assisted RTM process. Based on L9(3⁴) orthogonal table, joint dimension (w/d: sample width/hole diameter, e/d: edge distance/hole diameter);clamping torque and modified non-woven material and three levels were selected respectively to study the effect of multi-factor collaboration on the joint performance of single screw double lap bolts of GF/VE composite materials. The results show that when w/d is 2, e/d is 6, the clamping torque is 9, the bolt connection strength of the modified GF/VE composite material with TPU non-woven fabric between layers is the largest. The influence of w/d on the joint strength of composite material is greater than that of e/d. When w/d and e/d is greater than 3, the composite material will not fail immediately after reaching the maximum load, while when w/d and e/d is less than 3, the composite material will fail immediately after reaching the maximum load. The morphology of the fracture was analyzed by SEM, and it was found that the fracture surface between the layers of the sample was uneven, and there were granular dispersed phases on the matrix resin between the layers. This was caused by the blending of the thermoplastic film with the vinyl ester resin after heating and melting. This phenomenon helps to enhance the bond strength between the fiber and the resin.

PREPARATION AND PROPERTIES OF MODERATE TO LOW TEMPERATURE CURING CARBON FIBER PREPREG

LIAO Guo-feng, YANG Xiao-bing, LV Piao-piao, YE Guo-fang

2020, 0(12): 59-63.

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The epoxy resin system were developed, which can be cured at moderate to low temperatures and suitable for hot-melt processing of perpergs. The formulation and curing system of the resin system were determined by analyzing the viscosity-temperature change of the resin system, the gel time-temperature relationship and the curing characteristics. The effects of temperature and pressure of the drum on fiber wettability were studied. The results show that the preperg T700 carbon fiber perperg exhibits good processibility and mechanical properties. Moreover, the longitudinal tensile, longitudinal compressive, bending strength, short beam shear strength of the T700 carbon fiber perperg was 2588 MPa, 1229 MPa, 1749 MPa, and 83 MPa, respectively.

STUDY OF COMPRESSIVE STRENGTH OF COMPOSITE STRUCTURE WITH DELAMINATION

ZHANG Dong-zhe, LIN Zhi-yu, LIN Ren-bang, YANG Yan-zhi

2020, 0(12): 64-73.

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The compression test of composite laminates with different delamination damage was carried out, the ultimate load and failure mode of composite laminates with different delamination damage was recorded, and the influence of delamination on the compressive strength of composite laminates was analyzed. Based on ABAQUS platform, a finite element model of composite structure with delamination was established. Hashin criterion and Camanho criterion were introduced by wrote UMAT subroutines to study the generation and evolution of fiber or matrix damage. Virtual crack closure technology (VCCT) was used in combination with B-K criterion to calculate delamination expansion. Finally, the simulation results are compared with the test results to verify the correctness of the simulation model. Using the same method, the influence of radian, size and position of delamination on failure mode and compressive strength of curved composite laminates was analyzed. The results show that the residual compressive strength of curved composite laminates with larger radian is higher than that of flat composite laminates. If the radian of the curved composite laminates is small, the larger the delamination size, the smaller the residual compressive strength of the curved composite laminates. The deeper the position of delamination, the greater the residual compressive strength of the curved composite laminates.

THE COUPLING EFFECT AND DAMAGE ANALYSIS DURING DRILLING CFRP LAMINATES WITH PLANE RAKE FACE TWIST DRILLS

LIU Li-ping, ZHANG Fang, LIAN Bo, ZHOU Chang-geng

2020, 0(12): 74-80.

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In this paper, three plane rake facetwist drills with different rake angles were used to drill CFRP composite laminated with different processing parameters. This paper focuses on the influence of the coupling effect of rake angle, spindle speed and feed speed on the damage of borehole exit based on CFRP composite. The experimental results show that the coupling effect between the rake angle, the feed speed and the spindle speed can change the immediate pushing effect, the cutting effect and the physical properties of the borehole exit, and further affect the damage of the borehole exit. When the rake angle is 26°, the feed speed is 200 mm/min and the rake angle is 30°, the feed speed is 50 mm/min, the damage at the borehole exit firstly decreases and then increases with the increase of the spindle speed. Finally, according to the experimental results, the optimum processing parameters of each plane rake face twist drill are given.

EFFECT ON EQUIPMENT TRAVEL OF PRESSING ON NEGATIVE CURVATURE CYLINDER WITH ANGLE

WANG Xian-feng, ZHAO An-an, TANG Shan-shan, WANG Hao-jun

2020, 0(12): 81-83.

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Because of the condition of limited mould size or limited equipment travel, negative curvature cylinders is difficult to place prepreg on it. This research focus on how to expand fiber placement area on negative curvature cylinders. In order to avoid the lack of equipment travel and expand the scope of equipment operation, this article propounds a method of giving angle pressure on cylinders. This research includes modeling, parameter analysis and conclusion. Firstly, the model of inclined pressure should be established and the influencing factors are summarized and analyzed, such as the length of fiber placement head, the radius of the cylindrical surface of the negative curvature, and the angle range. Then the influence trend of the parameters and the level of influence at different placement positions is analyzed in detail. After analysis, a reasonable influencing range of pressure angle is given. Finally, according to the actual situation, the angle scheme is given and the actual fiber placement verification experiment is carried out. As a result, the effectiveness of the algorithm is verified by those experiments. This algorithm also lays a theoretical foundation for the use of angle pressure to increase the fiber placement area or avoid the lack of equipment travel in negative curvature surface placement.

IMPACT PROPERTIES AND SYNERGISTIC EFFECT OF NYLON 6 BASED COMPOSITES

LI Yan, YIN Hong-feng, QIN Yue, YANG Shun

2020, 0(12): 84-91.

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This paper studies the effect of different reinforcements on the impact properties and synergistic reinforcement of nylon 6 composites, and analyzes the reasons for its enhancement. The binary, ternary and quaternary nylon 6 (PA6) matrix composites were fabricated by melt-extrusion, anodic oxidation and hot pressing method. The fracture morphologies of multi-scale reinforcement reinforced PA6 matrix composites under impact stress were characterized by FESEM. The impact properties and reinforcement mechanisms of inorganic particles (IP), carbon fibers(CF) and metal-reinforced nylon 6 composites were studied. The results show that: ① There is a certain synergistic effect in inorganic particle and carbon fiber multi-scale co-reinforced PA6 matrix composites, which can significantly improve the impact properties of the composites. The impact strength of GB, CF, and metal co-reinforced PA6 composite reaches 94.7 kJ/m². ② Micron-sized glass beads (micro GB)debond under impact stress, which deflected and pinned the crack propagation. ③ Nano CaCO₃ debonds under impact stress and produces the micro-cracks and crazes, which help the reinforcement of the glass beads and carbon fibers. ④ The failure modes of fiber metal laminate under impact stress are the debonding, fracture and pull-out of fiber, tensile fracture of the matrix, the plastic deformation, fracture and oxide layer cracking of the metals, and the interfacial debonding of the metal to substrate.

STUDY ON TOUGHENING MODIFIED BISPHENOL A EPOXY RESIN BY VINYL ESTER RESIN

CHEN Feng, WANG Shu-xia, ZHAI Jun-ming, GUO Jian-jun

2020, 0(12): 92-99.

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Toughening of epoxy resins has been a research hotspot for polymer scientists and mechanics experts. However, the epoxy resin is cross-linked to formed a three-dimensional network structure. The structure has high crosslink density and high internal stress, which results in increased brittleness of the material, poor impact toughness and easy cracking. Aiming at the above problems, the method of simultaneous curing of vinyl ester resin (854) and epoxy resin (5241) was used to toughen and modify the epoxy resin. The curing process of the mixed system was studied by rotational viscosity and DSC, and the curing system was determined. In addition, the glass transition temperature, thermodynamic properties and mechanical properties of the fiber reinforced material were studied by DMA, TG and mechanical tests. In particular, when phr (5241∶854)=80∶20, the impact strength of the casting matrix is as high as 15.4 kJ/m², which is 41.3% more than that of pure epoxy resin, and the impact strength of the corresponding fiber reinforced material has reached 605 kJ/m². At the same time, the tensile strength is maintained at 1090 MPa and the maximum storage modulus is only 13 GPa. Therefore, the system has the best comprehensive mechanical properties. Furthermore, the cross-section morphology of the casting matrix was observed by SEM photos and the possible fracture mechanism was inferred.

EFFECT OF DEFECTS IN VARIABLE ANGLE TOW PLACEMENT (VAT) ON MECHANICAL PROPERTIES OF COMPOSITES

WANG Yi-min, YAN Chun-yun, LIU Ting, GAO Zhi-cheng

2020, 0(12): 100-104.

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VAT (Variable Angle Tow Placement) is an international advanced computer-controlled fiber preform forming process of fiber reinforced plastics. In this paper, three kinds of multiple product defects and defect degree of VAT process were designed, and 10 kinds of CFRP plates were made by VARI process. Ultrasonic phased array C-scan and SEM were used for macroscopic examination and microscopic characterization. The longitudinal tensile and compression tests of CFRP were carried out to study the effect of unidirectional laying defects on the mechanical properties of CFRP sheet. It is very beneficial for VAT process to be further improved, quality system to be established and benefit to be improved.

RESEARCH ON PREPARATION AND THERMAL PERFORMANCE OF HOLLOW FABRIC COMPOSITE BATTERY PACK

JI Zeng-xiang, SUN Qian-qian, JIANG Chun-yang, WANG Kun

2020, 0(12): 105-108.

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Different structural insulation materials were compared and studied, and the structural strength and maximum displacement of the hollow fabric composite battery pack were calculated by simulation. This design can not only meet the insulation requirements, but also occupy no extra space. In order to verify the thermal insulation performance of the hollow fabric composite material pack, a sample of the hollow fabric composite battery pack was prepared by the hand lay-up process, and a thermal insulation test was performed on the composite pack. The test results show that the heat preservation time of the hollow fabric composite battery pack is longer than that of the metal box.

STUDY ON PREFORM TECHNOLOGY OF C-BEAM HOT DIAPHRAGM OF DOMESTIC T800 HIGH TOUGHNESS EPOXY RESIN MATRIX COMPOSITE

JIANG Shi-cai, AN Xue-feng, YAN Li, CUI Jing-cheng

2020, 0(12): 109-114.

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During the curing process of AC531 resin rich in thermoplastic toughening agent in domestic T800 composite, due to the existence of reinforcement fiber, the dissolution phase separation behavior of thermoplastic toughening agent in epoxy resin matrix occurs simultaneously with the curing process of epoxy resin. Macroscopically, the viscosity temperature curve of AC531 resin matrix becomes complex because of the obvious process of increasing and decreasing viscosity between 120 ℃~160 ℃, which will inevitably affect the molding process of domestic T800 composite. According to the change of resin viscosity and slip resistance after holding at different temperature and time, 100 ℃ for (30~40) min was selected as the molding condition. On this basis, two kinds of C-shaped spars with no curvature (basic type) and strip curvature are prepared. The results show that T800 made in China has good membrane forming technology and can be used to prepare C-wing beam. However, for C-type wing beam with curvature of edge strip, due to its undevelopable geometry, obvious fold phenomenon occurs at the hyperbolic interface formed by the R-zone of the flange and the curved surface.

RESEARCH ON FREQUENCY SELECTIVE AND WAVE-TRANSPARENT PROPERTIES OF CYANATE ESTER RESIN REINFORCED BY QUARTZ FIBRE

LI Qing, CHE Yong-xing, ZHAO Jing, CHAI Peng-jun

2020, 0(12): 115-120.

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Quartz fibre was used as reinforcement materials, cyanate ester resin was used as matrix, aramid paper honeycomb was used as core, cyanate ester resin/acetone solution was used as impregnating solution, skin plate, A-sandwich and C-sandwich composite plate were prepared with vacuum bag molding process. Mechanical properties was tested, the influence of different impregnating solution ratio on mechanical properties was studied. When the ratio is 1∶1,it shows best mechanical properties, which meets the strength requirement for radome. The influence of sandwich composite skin's thickness on electrical properties was investigated. It was found that when the skin's thickness is 0.6 mm, the loss of electromagnetic beyond 14 GHz is obviously decreased. Two types of FSS was embedded into A-sandwich and C-sandwich structures respectively, it meets the frequency selective and wave-transparent function in two frequency channel (channel Ⅰ: 33 GHz~34 GHz; channel Ⅱ: 11.5 GHz~14.5 GHz).

A REVIEW OF SURFACE DEFECT INSPECTION TECHNOLOGY OF AUTOMATED FIBER PLACEMENT MANUFACTURING

MA Shao-bo, WEN Li-wei, WANG Ruo-zhou, SONG Gui-lin

2020, 0(12): 121-128.

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As carbon fiber reinforced plastics (CFRP) become more integrated into the design of large single piece aircraft structures, a new method was developed which is called Automated Fiber Placement (AFP) to improve the efficiency and quality of CFRP manufacturing. AFP systems allow the repeatable placement of uncured, spool fed carbon fiber tape onto substrates in desired thicknesses and orientations. This automated process may incur defects, such as overlapping, gaps, twists which can severely undermine the structural integrity of the part and decrease its property. Current defect detection and abatement methods are very labor intensive, and still mostly rely on human manual inspection. This part of work is time consuming and vulnerable to human error. Studies have shown that manual inspection can consume more than 20% of total production time. The academia is responding to this by focusing on the development of automated inspection systems. This article describes different inspection methods for automated fiber placement process, including traditional methods, laser projectors, thermal camera, profilometers, machine vision and machine learning. Manual inspection with laser projectors can get higher accuracy but still need manual labor. Thermal camera and machine vision basically identify defects from image which might includes noises. Using profilometer is a promising method because the data from it describes accurate profile of surface. Every method has its own advantages and disadvantages, there are still many major problems need to be solved in AFP defect inspection.

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