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1.
In this study a methodology to assure easy debonding of adhesive joints by combining the inductive heating method and the use of thermally expandable particles (TEPs) was developed. Two commercially structural adhesive systems used in the automotive industry (one polyurethane and one epoxy) were tested. First, the influence of TEPs content on the lap-shear strength of the TEPs-modified single lap joints was investigated. Further, the ability of the TEPs-modified joints to support temperature controlled debonding was evaluated. It was showed that the control of the debonding process by temperature is possible. The temperature needed for debonding is a function of TEPs content and can be lowered by increasing the TEPs content. 相似文献
2.
In this work, a hot-melt adhesive used by automotive industries for bonding plastic components has been modified with three different percentages of nanofiller (iron oxide) in order to make the adhesive electromagnetically sensitive and to perform adhesive joint separations. Fe3O4 particles with a weight concentration of 3%, 5% and 10% were embedded in the adhesive matrix. Single Lap Joint (SLJ) tests showed that a slight increase of the maximum load and a more ductile behaviour are obtained. The sensitivity of these modified adhesive performance to the induction heating process was studied with respect to some relevant parameters: the current (or power), the frequency of the electromagnetic induction field and the shape of the coil. Furthermore, the diameter of the hollow copper coil was modified in order to understand whether the coil temperature has an effect on the separation time. The separation time, that is an index of the time needed to reach the melt of the adhesive and the consequent SLJ separation, together with the temperature profile of the adhesives have been used to evaluate the sensitivity of these adhesives to the process parameters. The analysis on the temperature and separation time showed that the most influencing parameter is the frequency of the electromagnetic induction field. As expected, also the shape of the coil influences the separation time, in particular, the adhesive joint separated with the pancake coil showed lower values of the separation time compared to the solenoidal coils. Scanning Electron Microscope (SEM) showed that iron oxide particles tend to form small agglomerate that resulted well dispersed in the adhesive matrix. Thermogravimetric analysis (TGA) was used to verify that the separation procedure do not degrades these modified adhesives. 相似文献
3.
Shanti V. Nair 《Journal of the American Ceramic Society》1990,73(10):2839-2847
Solutions are obtained for the mechanics of debonding in the crack wake in fiber- or whisker-reinforced composites for the case where a finite shear traction exists at the fiber/matrix interface in the debonded zone. These solutions are then applied to derive expressions for the steady-state toughness increases obtained in bonded composites wherein the toughness contribution is provided by crack-wake fiber/matrix debonding and crack bridging. The solutions for an unbonded composite containing a frictional fiber/matrix interface can be obtained from the derived equations in the limit of the fiber/matrix interface toughness equal to zero. In this limit, the debond crack length reduces to the slip length and the expressions for the crack opening and the predicted toughness increase reduce to previously derived expressions for unbonded composites. The steady-state toughness is found to depend sensitively on the interface toughness, the fiber fracture strength, and the shear tractions in the debonded zone including other material parameters, such as fiber radius and volume fraction and the moduli of the constituent phases. It is shown that in order to obtain finite toughness increases, the fiber/matrix interface toughness must be less than a critical value dependent on the fiber fracture strength, fiber radius and volume fraction, and fiber and matrix moduli. The predictions of the model are applied to published experimental results from a detailed and complete study of toughness increases in a bonded whisker-reinforced composite. 相似文献
4.
Longbiao Li 《International Journal of Applied Ceramic Technology》2019,16(1):97-107
In this paper, the effect of fiber debonding on matrix multicracking development of different fiber-reinforced CMCs is investigated using the micromechanical approach. The Budiansky–Hutchinson–Evans shear-lag model is adopted to analyze the fiber and matrix stress distributions of the damaged composite. The fracture mechanics approach is used to determine the fiber/matrix interface debonding length. Combining the critical matrix strain energy criterion and fracture mechanics fiber/matrix interface debonding criterion, the stress-dependent matrix multicracking development is analyzed for different fiber volume fraction, fiber/matrix interface properties and matrix cracking characteristic stress. The experimental matrix multicracking development of unidirectional C/Si3N4, SiC/Si3N4, SiC/CAS, SiC/CAS-II, SiC/SiC, SiC/Borosilicate and mini-SiC/SiC composites are predicted. 相似文献
5.
Panos G. Charalambides 《Journal of the American Ceramic Society》1990,73(6):1674-1680
The competition between initial fiber debonding versus fiber failure marks a crucial event of the microstructural failure process in fiber-reinforced brittle matrix composites. In this study, the role of a thermal residual stress field on the debonding conditions is examined theoretically and analytically. The analysis is based on two critical observations, the first being that the mechanics at the tip of a kink crack are driven only by the singularity at the main crack tip. Following from the first is the second observation that any thermal stress effects on the debonding criteria should enter only through the phase angle ψ T of the total stress intensity factor at the main crack tip. In general, this stress intensity factor has a thermal as well as a mechanical load contribution. It is shown that when the thermal and mechanical stress intensities, K R and K t , respectively, are in phase , i.e., ψ R =ψ t , the existing debonding conditions are universal and can be used even in the presence of thermal loads. On the contrary, when K R and K t are out of phase , i.e., ψ R ≠ψ t , events such as the delamination of thick films or debonding of inclined aligned fibers in brittle matrix composites become sensitive to the presence of the thermal stresses. 相似文献
6.
以热膨胀微球、石蜡和石墨为原料制备了一种快速修复混凝土裂缝的新型微波加热自修复功能材料(MHSFM)。研究了热膨胀微球掺量对MHSFM体积膨胀率的影响,测试了在微波作用下MHSFM和掺加MHSFM砂浆的升温速率,评价了MHSFM掺量对砂浆力学性能、抗渗性能和自修复性能的影响。结果表明,MHSFM的体积膨胀率随着热膨胀微球掺量增加而增大。在微波作用下,砂浆的升温速率随MHSFM掺量的增加而明显加快。MHSFM对砂浆的力学性能和抗渗性能有一定的影响,但会显著增强砂浆的自修复性能,掺加12%(质量分数)MHSFM的砂浆在微波作用下可快速愈合0.53 mm的裂缝。 相似文献
7.
Jin Uk Ha Ye Jin Hwang Sun Kyoung Jeoung Pyoung-Chan Lee Soo Young Kim Joo Kyung Park Jung Teag Kim Ji Hyun Yeom 《应用聚合物科学杂志》2019,136(19):47499
In this study, functional microcapsules (FMs) were designed for controlling the curing time and temperature of epoxy through modifications to thermally expandable microcapsules. The FMs were prepared with a mixture of liquid hydrocarbons and N,N-dimethylbenzylamine in the core, and acrylonitrile (AN)—methyl methacrylate copolymer or AN–methacrylate copolymer were used for the shell. Since the FMs were intentionally designed to have thermally vulnerable polymeric shells, the catalyst in the core could be released at the designated temperature. Therefore, FMs do not activate in epoxy at room temperature; rather, the FMs only become functional when the epoxy is cured under a heated atmosphere. Released catalyst at the higher temperature was confirmed by pyrolysis gas chromatography–mass spectrometry and optical microscopy. This study shows that the results will depend on the different compositions of liquid hydrocarbons and catalyst. Particle size of the capsules was changed with different ratio of catalyst and liquid hydrocarbon at the core and type of polymeric shell. Differential scanning calorimetry and rheometer results showed that higher catalyst loading resulted lower in crystalline and shear thickening temperature, respectively. Adhesion strength of epoxy containing FMs was analyzed by lap shear strength in order to detect the void effect due to released gas from the FM. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47499. 相似文献
8.
ABSTRACTThe expansion characteristics of thermally expandable microcapsules (TEMs) under hydrostatic pressure or in resin were experimentally investigated. For the experiments, the expansion of the microcapsules was observed in high-pressure nitrogen at high temperature utilizing optical microscopy with a digital camera installed. The TEMs used for the experiments were expanded by heating under hydrostatic pressure up to 3 MPa, but the expansion degree decreased with increasing pressure. A cured bulk specimen of epoxy resin containing the microcapsules was made, and the expansion of the microcapsules was again observed with the microscope. It was found that the expansion of the microcapsules in the resin was saturated at a certain temperature. The stress distribution in the resin produced by the expansion of the microcapsules was calculated by the finite-element method. It was found that normal stress occurred, but it was mainly compressive. Tensile stress was also generated, although the maximum value was smaller than that of shear stress. It was observed that the expansion of the microcapsules was limited when there were many microcapsules in the vicinity of the interface. In other words, a complicated stress state occurred, inducing interfacial failure along the interface. 相似文献
9.
The rise of miniaturized, integrated, and functional electronic devices has intensified the need for heat dissipation. To address this challenge, it is necessary to develop novel thermally conductive polymer composites as packaging materials. In this paper, a number of factors for the construction and design of thermally conductive polymers are concluded. Special attention is focused on the analysis and comparison of the thermally conductive composites prepared by various fillers or strategies to provide guidelines and references for future design of composite materials. The current commonly used preparation strategies of thermally conductive polymer are summarized, such as using a variety of fillers, vacuum filtration, template method, and so on. The challenges of thermally conductive polymer composites are finally sketched. This review can inspire the design of polymer composites with brilliant thermal conductivity. 相似文献
10.
An approach is offered for evaluation of effective stress-strain curves of participate composites under plane strain conditions based on absolution of the boundary-value problem providing simultaneously the data on the corresponding structural stress and strain fields. The influence of randomness in the particle arrangements and the filler concentration on the effective behavior is established. It is demonstrated that the observed plateaus on the tensile and compressive curves are caused to a degree by the geometrical non-uniformity of the composite structures. The difference between tensile and compressive curves is examined and explained from the structural point of view. 相似文献
11.
Abstract Novel ultralight porous fiber-based composites are a very attractive subject in the material chemistry and are enabled to promise applications in the sound absorption fields. In this work, it reported a facile strategy to prepare the flame-retardant, sound-absorbing, and mechanical enhancement porous fiber-based composites (PFC-EM-x) by using natural cellulose fiber, glass fiber, and flame retardant. Subsequently, the expandable microspheres (EMs) were added to construct the well-defined porous microstructure of materials for the enhancement in sound-absorbing performance. The results demonstrated that the high EMs contents had a remarkable influence on the porous structure of the composites so that the composites achieved the outstanding sound-absorbing performance and acceptable mechanical properties compared with other reported materials, especially as-prepared PFC-EM-20 composite showed excellent sound absorption at a range of high frequencies with the maximum sound absorption coefficient of 0.781 and tensile strength of 1.07?kN/m. Moreover, the limiting oxygen index values of all the samples were more than 26, both V1 and V2 rating in UL-94 test were achieved, which indicated that the obtained PFC-EM-x composites displayed outstanding flame retardancy. In summary, this study provides a facile strategy to rationally construct mechanically robust, highly efficient sound-absorbing and flame retardant ultralight composites which have promising applications in the future as green engineering materials. 相似文献
12.
采用碳布层叠然后用化学气相渗方法制备了C/SiC复合材料,这种材料纤维与基体间的界面是决策材料力学行为的重要因素,带有热解碳作为界面层的C/SiC材料,在断裂进表现出大范围的脱粘,纤维与周围的基体不同发生断裂,有大量的纤维拨出,断口类似毛刷,无界央层材料表现为脆性平面断口,裂纹直接通过纤维和基体向前扩展,没有发生脱粘。 相似文献
13.
Hua Zhou Liangdong Ye Dongming Chen Ziwei Li Shanrong Li Dacheng Li Zhiyi Huang Zhouqiao Wei Shaorong Lu 《乙烯基与添加剂工艺杂志》2023,29(6):991-1001
Graphite is a thermally conductive filler. However, when dispersed into high density poly(ethylene) (HDPE) resin, graphite particles tend to agglomerate and requires a compatibilizer to achieve desired thermal/physical properties. In this study, oleic acid (OA), a bio-based additive and polyethylene-polyamines (PEPA) were used to synthesize a new compatibilizer, PEPA-g-OA, containing numerous NR2 groups. The experimental results showed that PEPA-g-OA can significantly improve the compatibility between graphite particles and the HDPE matrix due to uniform dispersion of graphite in the HDPE matrix. When the graphite content was 25 wt%, the thermal conductivity of the composite recorded 1.2 W m−1 K−1 (three times that of neat HDPE) and the volume resistivity was 1.8 × 109 Ω cm, indicating excellent electrical insulation. Compared to the composites with no graphite content, the properties of the composites with 25 wt% graphite content exhibited narrower melting and crystallization peaks, more stable mechanical properties, and higher ultraviolet aging resistance. Synthesized new bio-based compatibilizer and thermally conductive and electrically insulating composites developed in this study can be useful in different industrial fields for the preparation of the next generation composites. 相似文献
14.
Effects of interface bonding properties on cyclic tensile behavior of unidirectional C/Si3N4 and SiC/Si3N4 composites
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Longbiao Li Pascal Reynaud Gilbert Fantozzi 《International Journal of Applied Ceramic Technology》2018,15(5):1124-1137
In this paper, the effect of fiber/matrix interface bonding properties on the cyclic loading/unloading tensile stress?strain hysteresis loops of 2 different ceramic‐matrix composites (CMCs), ie, C/Si3N4 and SiC/Si3N4, has been investigated using micromechanical approach. The relationships between the damage mechanisms (ie, matrix multicracking saturation, fiber/matrix interface debonding and fibers failure), hysteresis dissipated energy and internal frictional damage parameter have been established. The damage evolution processes under cyclic loading/unloading tensile of C/Si3N4 and SiC/Si3N4 composites corresponding to different fiber/matrix interface bonding properties have been analyzed through damage models and interface frictional damage parameter. For the C/Si3N4 composite with the weakest fiber/matrix interface bonding, the composite possesses the lowest tensile strength and the highest failure strain; the hysteresis dissipated energy increases at low peak stress, and the stress?strain hysteresis loops correspond to the interface partially and completely debonding. However, for the SiC/Si3N4 composite with weak interface bonding, the composite possesses the highest tensile strength and intermediate failure strain; and the hysteresis dissipated energy increases faster and approaches to a higher value than that of composite with the strong interface bonding. 相似文献
15.
《Ceramics International》2016,42(15):16535-16551
The hysteresis loops of C/SiC ceramic-matrix composites (CMCs) with different fiber preforms, i.e., unidirectional, cross-ply, 2D and 2.5D woven, 3D braided, and 3D needled at room temperature have been investigated. Based on fiber slipping mechanisms, the hysteresis loops models considering different interface slip cases have been developed. The effects of fiber volume fraction, matrix cracking density, interface shear stress, interface debonded energy, and fibers failure on hysteresis loops, hysteresis dissipated energy, hysteresis width, and hysteresis modulus have been analyzed. An effective coefficient of fiber volume fraction along the loading direction (ECFL) was introduced to describe fiber preforms. The hysteresis loops, hysteresis dissipated energy and hysteresis modulus of unidirectional, cross-ply, 2D and 2.5D woven, 3D braided and 3D needled C/SiC composites have been predicted. 相似文献
16.
双弹簧、双活塞力学模型在颗粒填充聚合物复合材料粘弹性质描述中的应用研究 总被引:2,自引:0,他引:2
黄传辉;陶健;张广印;郭勤建 《中国塑料》2009,23(6):65-68
推导了双弹簧、双活塞黏弹性力学模型的本构方程。在多功能试验机及轮廓摩擦磨损仪上考察了CuO、Al2O3及Cu等无机物颗粒填充聚酰胺1010复合材料的静态蠕变特性和松弛特性。实验结果表明,该力学模型能较好地反映颗粒增强聚合物复合材料的黏弹性质。 相似文献
17.
18.
The halogen‐free flame‐retardant polystyrene (PS) composites containing expandable graphite (EG) and melamine phosphate (MP) were prepared successfully, and the thermal degradation behavior and fire performance were investigated by various measurements. The experimental results show that EG and MP have a synergistic effect on flame‐retardant PS, which can catalyze the char formation from PS. PS/MP/EG(1:2) composite achieves limited oxygen index value of 28.0% and UL‐94V‐0 (1.6 mm) rate. The mass retention at high temperature (800 °C) under air atmosphere of PS composites have a large increase by the introduction of EG and MP. Microscale combustion calorimeter (MCC) and cone calorimetric analysis indicate that the heat release rate and total heat release of PS/MP/EG(1:2) composite are reduced significantly, because the formed thick char layer has a notable barrier property. The study on the char residue of PS/MP/EG(1:2) composite by X‐ray photoelectron spectroscopy (XPS) analysis confirms the formation of the stable structures containing P? O? C. Furthermore, the mechanical properties of PS composites were also investigated; compared with neat PS, the addition of flame retardants leads to the decrease of tensile strength and flexural strength, but the impact strength of PS/MP/EG(1:2) has increased by 44.2%. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45474. 相似文献
19.
《Ceramics International》2020,46(17):27031-27045
In this paper, a time-dependent vibration damping model of fiber-reinforced ceramic-matrix composites (CMCs) is developed. Considering time and temperature dependent interface damages of oxidation, debonding, and slip, the relationships between composite vibration damping, material properties, internal damages, oxidation duration and temperature are established. The effects of material properties, vibration stress, damage state, and oxidation temperature on time-dependent composite vibration damping and interface damages of C/SiC composite are discussed. The time-dependent composite vibration damping decreases with fiber volume, matrix crack spacing and interface shear stress, and increases with vibration stress. The experimental composite vibration damping and internal damages of 2D C/SiC composite for different oxidation duration t = 2, 5 and 10 h at elevated temperatures T = 700, 1000 and 1300 °C are predicted. When the oxidation duration was short (i.e., t = 2 h), the composite vibration damping decreased with temperature; however, when the oxidation duration was long (i.e., t = 5 and 10 h), the composite vibration damping decreased with temperature below 1000 °C, and increased with temperature to 1300 °C. 相似文献