周期性叠层材料的成型和制备新技术

叠层复合是一种新型的复合构型,它具有提高材料断裂韧性和抗弯强度的优异特性,对优化陶瓷的力学性能十分有效。本文对叠层材料的不同成型和制备工艺,特别是有我们自己特色的沉降成型、制备工艺作了综述性研究。     

Effect of insulation layer for thermal shock in cryogenic composite laminates

The structural weight of a cryogenic propellant tank for reusable launch vehicles (RLVs) can be effectively reduced by the use of advanced composite materials. However, microscopic damage such as transverse matrix cracks (TMC) and delaminations are prone to develop in composites well below the load levels that would result in mechanical failure. This microscopic damage leads to a leakage path for the fuel. The leakage is influenced by many factors including connectivity of the cracks, residual and service‐induced stresses, and composite stacking sequence. This article is concerned with the effect of thermal gradients due to sudden exposure to a cryogenic temperature with and without insulation layer. An investigation of the insulation layer for sudden exposure to cryogenic temperatures is conducted numerically. The exposure of the harsh environment could make the damages such as delaminations, TMC, and leakage path. The defects from manufacturing could be formed, and they are critical parts under sudden exposure to cryogenic temperature. Therefore, the qualitative analysis for insulation technique is needed. The results from this article are very important because the stress levels which cause damages can be predicted and also controlled using the insulating techniques. The insulation skill which can suppress the stress levels is newly introduced in this article for RLV cryogenic fuel tank. Moreover, the effect of lay‐ups is also investigated in this article. The thermal gradient can be controlled by using different lay‐ups. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Epoxy-functionalized polysiloxane reinforced epoxy resin for cryogenic application

The poor cryogenic mechanical properties of epoxy resins restrict their extensive application in cryogenic engineering fields. In this study, a newly synthesized epoxy-functionalized polysiloxane (PSE) is used to improve the cryogenic mechanical properties of bisphenol-F epoxy resin. The Fourier transform infrared spectra and nuclear magnetic resonance confirm the formation of epoxy-functionalized –Si–O–Si– molecular chain. The surface free energy test results show that the PSE has a better compatibility with epoxy resin. The mechanical test results show that the cryogenic tensile strength, failure strain, fracture toughness, and impact strength of epoxy resin is improved significantly by adding the suitable amounts of PSE. Compared to the neat epoxy resin, the maximum tensile strength (196.92 MPa, an improvement of 11.2%), failure strain (2.97%, an improvement of 33.8%), fracture toughness (3.05 MPa·m^1/2, an improvement of 30.7%) and impact strength (40.55 kJ m⁻², an improvement of 14.8%) at cryogenic temperature (90 K) is obtained by incorporating 10 wt % PSE into the neat epoxy resin. Moreover, the results also indicated that the tensile strength, Young's modulus, and fracture toughness of epoxy resin with the same PSE content at 90 K are higher than that at room temperature (RT). © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46930.     

Electrical properties of laminated epoxy-carbon fiber composite

This work deals with the effect of temperature on the electrical properties of laminated epoxy composites containing 60% by volume of commercial unidirectional carbon fibers. The temperature was varied from 30°C to 120°C and the frequency range was from 10 Hz to 10 kHz. It is found that the impedance decreases with increasing temperature and is inversely proportional to the number of layers in the specimen. The calculated dielectric constants show a strong dependence on the frequency below 100 Hz, and attain relatively constant values for frequencies greater than 100 Hz. The decrease in impedance with increasing number of layers was explained in terms of the existence of electrical contacts and bridges both between and within the fibers, in the carbon fiber layers. The activation energy results indicate that there are two conduction mechanisms in this laminated composite.     

Mechanical and fracture mechanical characterization of building materials used for external thermal insulation composite systems

Fracture mechanical investigations of building materials applied for external insulation composite systems have been performed in order to provide material data for the numerical simulation of mechanical failure. For this purpose a wedge splitting procedure according to Tschegg has been employed and modified for the investigation of material layers with a thickness of approx. 5 mm. The testing method proved to be suitable for investigation of both the materials themselves and the compound of two layers. Results of commercially available building materials for external insulation composite systems are shown. From their dependence on different preparation procedures, it may be concluded how temperature and humidity may affect material properties under conditions of actual service.     

Synthesis and characterization of Cu1-xZnxO composite thin films for sensor application

Cu_1-xZn_xO composite thin films were prepared using industrially applicable spray pyrolysis technique for volatile organic compound (VOCs) sensor application. Sensing properties for different concentration of VOCs such as acetone, ethanol and methanol were studied at different sensor operating temperature. XRD studies on prepared thin films confirmed formation of CuOZnO composite thin films with presence of different peaks for monoclinic structured CuO and hexagonal structure ZnO, it was also observed that formation of composite material improves sensing property towards VOCs. Granular morphology observed from SEM images were also contributed to enhance sensitivity of Cu_1-xZn_xO thin films. Hot probe experiment reveals that all the thin films were p-type in conductivity nature. Maximum electrical conductivity was achieved for Cu_0.75Zn_0.25O composite thin films, which also showed highest sensing property for VOCs. Cu_0.75Zn_0.25O thin films were selective towards ethanol and were capable of detecting 1 ppm of ethanol at operating temperature of 290 °C.     

金属-树脂复合型低温结合剂的制备与性能的研究

文章主要针对金属结合剂自锐性差,树脂结合剂耐热性差的缺点,研发一种低温烧结复合型的金属-树脂结合剂。结合剂以铜粉、锡粉、锌粉、铅粉、银粉、树脂粉等为原料,先冷压成型,再热压烧结,当树脂含量为10%,温度460℃时,样条的硬度值达83.4HRB,强度值达145.5 MPa。最佳烧结工艺:温度460℃,保温时间1分钟,压力为0.5MPa。     

Mechanical and thermal enhancements of benzoxazine‐based GF composite laminated by in situ reaction with carboxyl functionalized CNTs

An easy and efficient approach by using carboxyl functionalized CNTs (CNT‐COOH) as nano reinforcement was reported to develop advanced thermosetting composite laminates. Benzoxazine containing cyano groups (BA‐ph) grafted with CNTs (CNT‐g‐BA‐ph), obtained from the in situ reaction of BA‐ph and CNT‐COOH, was used as polymer matrix and processed into glass fiber (GF)‐reinforced laminates through hot‐pressed technology. FTIR study confirmed that CNT‐COOH was bonded to BA‐ph matrices. The flexural strength and modulus increased from 450 MPa and 26.4 GPa in BA‐ph laminate to 650 MPa and 28.4 GPa in CNT‐g‐BA‐ph/GF composite, leading to 44 and 7.5% increase, respectively. The SEM image observation indicated that the CNT‐COOH was distributed homogeneously in the matrix, and thus significantly eliminated the resin‐rich regions and free volumes. Besides, the obtained composite laminates showed excellent thermal and thermal‐oxidative stabilities with the onset degradation temperature up to 624°C in N₂ and 522°C in air. This study demonstrated that CNT‐COOH grafted on thermosetting matrices through in situ reaction can lead to obvious mechanical and thermal increments, which provided a new and effective way to design and improve the properties of composite laminates. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Adhesion failure propagation in adhesively-bonded single-lap laminated FRP composite joints

This paper deals with three-dimensional non-linear finite element analyses to study the behaviour of embedded adhesion failure propagation in adhesively-bonded single-lap laminated FRP composite joints clamped at one end and subjected to uniform extension at the other end. Because of loading eccentricity and joint material heterogeneity, the embedded adhesion failure is likely to initiate from the stress singularity points and will propagate from either end of the adhesive layer along the adherend–adhesive interfaces. The effects of interaction of such failures and their propagations along the interfaces of the adherends and adhesive are the main concerns of this paper. The peel and shear stresses have been computed along the mid-surface of the adhesive layer for varying adhesion failure lengths to find out the influence of adhesion failure length on the strength of the joint being analyzed. The concept of fracture mechanics has been used to calculate the strain energy release rate (SERR) as the adhesion failure propagates using the virtual crack closure technique (VCCT). It is seen that mode-II SERR is predominant in the propagation of such adhesion failures. The SERR values computed with respect to the adhesion failure lengths being propagated from the two ends of the adhesive layer are seen to be different.     

Preparation and characterization of a Bacterial cellulose/Chitosan composite for potential biomedical application

Bacterial cellulose (BC)/Chitosan (Ch) composite has been successfully prepared by immersing wet BC pellicle in Ch solution followed by freeze-drying process. The morphology of BC/Ch composite was examined by scanning electron microscope (SEM) and compared with pristine BC. SEM images show that Ch molecules can penetrate into BC forming three-dimensional multilayered scaffold. The scaffold has very well interconnected porous network structure and large aspect surface. The composite was also characterized by Fourier transform infrared spectrum, X-ray diffraction, thermogravimetric analysis and tensile test. By incorporation of Ch into BC, crystallinity tends to decrease from 82% to 61%, and the thermal stability increases from 263 °C to 296 °C. At the same time, the mechanical properties of BC/Ch composite are maintained at certain levels between BC and Ch. The biocompatibility of composite was preliminarily evaluated by cell adhesion studies. The cells incubated with BC/Ch scaffolds for 48 h were capable of forming cell adhesion and proliferation. It showed much better biocompatibility than pure BC. Since the prepared BC/Ch scaffolds are bioactive and suitable for cell adhesion, these scaffolds can be used for wound dressing or tissue-engineering scaffolds.     

Development and characterization of composite chitosan/active carbon hydrogels for a medical application

Composite chitosan/active carbon (AC) hydrogels were elaborated by a novel route, consisting in exposing the chitosan solution to ammonia vapors. This vapor‐induced gelation method was compared with the conventional elaboration process, a direct immersion of the chitosan solution in liquid ammonia. The hydrogels were characterized to evaluate their potential application as wound‐dressings, mostly regarding their morphology, mechanical properties, swelling behavior, and sorption capacities for malodorous compounds emitted from wounds as diethylamine (DEA). The influence of elaboration route, chitosan concentration, and AC incorporation was studied. The results show that freeze‐dried hydrogels have a porous asymmetric structure dependent on the chitosan concentration and which promotes exudates drainage. The nanostructure of the parent hydrogel is semi‐crystalline and slightly dependent on the gelation conditions. It confers on hydrogel an acceptable mechanical behavior (compressive modulus up to 1.08·10⁵ Pa). Hydrogels including AC display enhanced sorption kinetics for DEA, with sorption capacities up to 49 mg g^?1. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and characterization of green urethane non-isocyanate from oleic acid for wood composite application

Conventional polyurethane (PU) is usually synthesized by a reaction between isocyanate and polyol. The use of isocyanate compounds is associated with significant health and environmental problems. Therefore, it is necessary to develop an environmentally friendly alternative method for manufacturing PUs without isocyanate routes. The aim of this research work was to synthesize green urethane from oleic acid, which included the following three stages: the synthesis of epoxidized oleic acid (EOA), the synthesis of carbonated oleic acid (COA), and the synthesis of green urethane from oleic acid (UOA). The resulting product was characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR) analyses, and by determining the iodine number, oxirane number, and hydroxyl value. The results of FTIR and NMR showed that EOA was successfully synthesized. The optimum COA synthesis process was obtained on TBAB catalyst usage of 1% (wt/wt) at 140°C for 48 h with a 500-rpm stirring rate and CO₂ gas flow rate of 0.2 mL/min with the resulting COA oxirane value of 0.00. The optimum condition of UOA synthesis through the aminolysis process resulted in the use of LiCl of 19.8% (wt/wt) at 70°C for 3 h with a stirring speed of 1200 rpm with a UOA hydroxyl number generated of 237.93 mg/mL.     

夹层玻璃的特性与应用

夹层玻璃是一种性能优良的安全玻璃 ,它是由两片或两片以上的玻璃 ,中间夹以聚乙烯醇缩丁醛( PVB)胶片 ,在一定的温度和压力下粘接而成的。它具有耐光、耐热、抗冲击强度高等特点 ,广泛应用于汽车、火车、轮船、飞机等运输工具及建筑方面。与传统的普通玻璃相比 ,夹层玻璃在安全、保安防护、隔音及防辐射等方面有着不可比拟的优良性能。1　安全特性当前 ,建筑对于采光的要求越来越高 ,采光面积占建筑物围护的面积比例越来越大 ,普通玻璃远远不能满足安全防护的要求。而夹层玻璃在受到超强度意外撞击被破坏时 ,玻璃的碎片被牢牢地粘结在聚…     

Mechanical and tribological assessment of composite AlCrN or a-C:Ag-based thin films for implant application

The present study focuses on the comparison of cathodic arc deposited AlCrN (ternary coating) and Ag alloyed a-C (amorphous carbon base coating) on chrome nitride (CrN) medical grade 316 LVM stainless steel. The work comprises of morphological, structural, nanomechanical and tribological evaluation in physiological simulated body fluid (SBF) lubrication following conditions pertaining to simulated hip joint. According to the findings, H/E, H³/E² and E_coating/E_substrate significantly effect the nanomechanical and tribological properties of the coatings. While a-C:Ag/CrN exhibited better L_y value compared to AlCrN/CrN due to better surface quality, the later has shown higher L_c2 value during nanoscratch test attributed to lower H³/E² and higher plastic work done. Inspite of lower friction coefficient, a-C:Ag/CrN observed higher wear rate during simulated tribotest attributed to low hardness, separate graphitic structure due to Ag doping and sudden increase of friction coefficient ascribed to severe abrasive delamination of a-C:Ag top layer. The wear mechanism observed under SEM microscopy indicate severe adhesion of Ti6Al4V counterbody on AlCrN/CrN coated surface. The size of wear debris obtained with AlCrN/CrN-Ti6Al4V tribopair was larger in size compared to a-C:Ag/CrN-Ti6Al4V tribopair. Nevertheless, despite inferior surface quality and lower L_y value and larger wear debris size, AlCrN/CrN coating performed better in nanoscratch (at L_c2 value) and demonstrated lower wear in simulated tribotest in physiological SBF condition.     

橡胶层合复合材料的疲劳损伤

研究了 (± 20° )钢丝帘线 /橡胶复合材料在单级和两级拉伸循环载荷下疲劳损伤的累积规律。结果表明：在载荷控制的疲劳过程中,材料的周期最大应变发展曲线呈现明显的三阶段规律;疲劳寿命与最大应力近似呈对数线性关系。各级载荷下,周期最大应变发展曲线都具有线性稳定增长的第二阶段。两级加载实验初步证明 Palmgren－ Minner法则仅适用于第一级疲劳条件比第二级疲劳条件轻缓的情况。     

Model of dynamic deformation of a laminated thermoviscoelastic composite

The phenomenological averaging method is used to construct the model of a laminated homogeneous thermoviscoelastic composite. To construct this model, we consider only phase properties. The system of equations of composite dynamics is closed by the equation of state (elastic potential), in accordance with which we calculate the stress and temperature. The equations obtained satisfy the Onsager symmetry principle and are thermodynamically correct. In deriving the equations we do not use the assumptions on regularity of layers and constancy of relaxation time; therefore, the kinetic coefficients can depend on the state of the medium.Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 4, pp. 123–131, July–August, 1993.     

Through-the-width delamination damage propagation characteristics in single-lap laminated FRP composite joints

Three-dimensional non-linear finite element analyses have been carried out to study the effects of through-the-width delaminations on delamination damage propagation characteristics in adhesively bonded single-lap laminated FRP composite joints. The delaminations have been presumed either to pre-exist or to get evolved due to coupled stress failure criteria in the laminated FRP composite adherends near the overlap ends beneath the ply adjacent to the overlap region. The out-of-plane stresses in the adhesive layer, the interlaminar stress distributions along the delamination fronts and the strain energy release rates (SERRs) corresponding to the three individual modes have been evaluated for varying positions of the delaminations pre-embedded in either of the adherends. A good matching between the present 3D results and experimental and analytical solution of the literature has been established for the undamaged and a damaged model. A significant difference in the interlaminar stresses and the SERR values has been observed and is largely dependent on the adherends (bottom or top) possessing the through-the-width delamination damages. Also, the interlaminar stresses and SERR values along the two corresponding delamination fronts are different. Accordingly, it can be concluded that the positions of the through-the-width delaminations significantly influence the delamination damage propagation behaviour vis-a-vis the performance of the composite joint.     

环氧树脂对层压复合用水性聚氨酯性能的影响

采用异佛尔酮二异氰酸酯(IPDI)、聚己二酸丁二醇酯(PBA)、二羟甲基丙酸(DMPA)、环氧树脂等原料制备了层压复合用水性聚氨酯(WPU)胶粘剂,考查了环氧树脂用量对其性能的影响。结果表明,随着环氧树脂用量的增加,WPU乳液黏度增加,粒径逐渐变大,稳定性变差;经环氧树脂改性的WPU,胶膜的耐水性优于未改性胶膜,力学性能得到提高。