Overview of Hydroxyapatite–Graphene Nanoplatelets Composite as Bone Graft Substitute: Mechanical Behavior and In-vitro Biofunctionality

Hydroxyapatite (HA) and related materials have been frequently studied as ceramic-based bone graft materials due to their outstanding biocompatibility and osteoconduction. Since the bones are the load supporting parts of a vertebrate, they must have good fracture toughness (K_IC) to avoid fracture at high loading during limb movements. However, the main shortcomings of HA are the poor fracture toughness and brittleness. The mechanical properties of HA need to be improved for orthopedic applications, therefore it is often fabricated with other materials into a composite. This article focuses on the effect of carbon nanostructures (CNSs) especially graphene nanoplatelets (GNPs) on the mechanical, physicochemical properties and in-vitro bio-functional performances of HA. We provide an overview on the preparation and characterization of the HA–GNPs composites. To conclude, the challenges in the fabrication of multi-substituted HA–GNPs composites and future outlooks in the biomedical domain are discussed.     

铁电/铁磁三相颗粒复合材料的磁电性能计算

采用格林函数方法给出了三相复合材料的磁电系数的解析式，对稀土-铁合金/压电陶瓷/高分子（Terfenol-D/PZT/PVDF）三相颗粒复合材料的磁电系数进行了计算.计算结果给出了复合材料的磁电性能与材料显微结构的关系，包括三相颗粒复合材料的磁电性能随组分、颗粒的长径比、PZT颗粒的电极化方向以及外磁场的变化趋势，可为实验设计提供参考和指导.通过合理设计，三相磁电复合材料的性能可以达到数百mV/A.作为一种新的磁电复合材料，三相颗粒复合材料有望成为一种新型高性能易制备的磁电材料. 关键词： 磁电效应 复合材料 格林函数     

Interfacial reactions and microstructure control in metal and intermetallic matrix composite processing

The achievement of the potential of composites for demanding applications where high specific strength and stiffness are required together with useful toughness is often limited by the available materials processing capabilities to develop specific reinforcement-matrix interface characteristics. Similarly, the elevated temperature stability of advanced composites is dominated by the behavior of internal interfaces. In order to develop effective processing strategies and stable composite designs, it is essential to consider the relevant phase diagrams which for most composites are at least of ternary order. On the basis of these diagrams, it is possible to select compositions of phases which possess desirable properties. In addition to phase diagram data, kinetic data such as the interdiffusion pathway and rates are required to understand and to control the possible interfacial chemical reactions in a composite system. From this basis, reinforcement coatings and barrier layers can be developed to control reactions and allow for in-service lifetime analysis. With solidification processing of composites, melt-reinforcement interactions involved in wetting, solidification reactions, and matrix microstructure evolution can also be evaluated in terms of the phase equilibria and kinetic pathways. Some applications of this approach have been demonstrated in the development of Ti- and A1-based composite systems.     

Effect of the silicone interlayer on mechanical properties of carbon fiber reinforced PMR-15 polyimide composites

Carbon fibers coated with various types and amounts of very high molecular weight silicones (780000 g/mol) are used to make unidirectional PMR-15 polyimide composites. Coating conditions have been found to affect the fiber arrangement within the interlayered composites which consequently has a strong effect on composite properties. The effect of variation of the type and the amounts of the silicone on the impact resistance, toughness and mechanical properties of the composite is determined. Retention of properties of the thermally aged composites has also been studied. Finally, the interlayered composites are checked for improvement of microcracking resistance.     

Fabrication and Characterization of Bioglass-Modified HA–ZrO2 Biocomposites

Hydroxyapatite (HA) being the main mineral constituent of human hard tissues is highly bioactive. Good chemical bonds can be generated between HA and natural bone. However, the low strength and inherent brittleness of HA restrict its application usually to non-load-bearing conditions. In this work, production of a new kind of HA–ZrO₂ composite by hot-press sintering method is described. Bioglass which has been widely used in reconstruction of damaged or diseased tissues was added into HA–ZrO₂ composites. Comparing with pure HA ceramic, this type of composite possesses better mechanical strength and retains the bioactivity of HA as well. The liquid phase generated by bioglass has been effective in improving the sintering process of HA–ZrO₂ composites. The phase composition of HA composite was characterized by XRD and their fracture surfaces were observed by SEM. The XRD results show that introducing a small amount of bioglass into HA–ZrO₂ composite cannot enhance decomposition of HA. The SEM images show that there were fewer pores on the fracture surfaces of HA–ZrO₂–bioglass composite than in the HA–ZrO₂ composite. The flexural strength and toughness of HA–ZrO₂ composite containing 2 wt% bioglass were 157 MPa and 1.63 MPa·m^1/2, respectively.     

Features of film growth during plasma anodizing of Al 2024/SiC metal matrix composite

Plasma anodizing is a novel promising process to fabricate corrosion-resistant protective films on metal matrix composites. The corrosion-resistant films were prepared by plasma anodizing on SiC reinforced aluminum matrix composite. The morphology and microstructure of films were analyzed by scanning electron microscopy. Specifically, the morphology of residual SiC reinforcement particles in the film was observed. It is found that the most SiC reinforcement particles have been molten to become silicon oxide, but a few tiny SiC particles still remain in the film close to the composite/film interface. This interface is irregular due to the hindering effect of SiC particles on the film growth. Morphology and distribution of residual SiC particles in film provide direct evidence to identify the local melt occurs in the interior of plasma anodizing film even near the composite/film interface. A model of film growth by plasma anodizing on metal matrix composites was proposed.     

Electroless plating of silver on cenosphere particles and the investigation of its corrosion behavior in composite silicon rubber

In this paper, silver coating on the surface of cenosphere particles was prepared by electroless plating method. The adhesion, oxidation resistance and corrosion resistance properties of silver coating mixed in silicone rubber were investigated. The corrosion characteristic of silver coating was evaluated by anodic polarization curves of the silicone rubber composite in sulfuric acid solution. The results showed that the silver coating on the surface of cenosphere particles was smooth and uniform. The silver film was not oxidized and peeling off during preparation of composite silicone rubber. The adhesion between the cenosphere particle and silver film was good enough. The anodic polarization curves of the silicone rubber composite showed typical activation and passivation transformation. The values of corrosion potential, the initiating passive potential and maintaining passivity potential of composites filled with different contents of Ag-coated cenosphere particles were the same and related to the nature of silver coating. The passive current density of composite increased with increase of the amount of Ag-coated cenosphere particles and was inversely proportional to the resistance of silicone rubber composite. The better the conductivity of silicone rubber composite is, the higher corrosion rate will be.     

Thermal and electrical conductivity of poly(l-lactide)/multiwalled carbon nanotube nanocomposites

Multiwalled carbon nanotubes (MWCNTs) are considered to be the ideal reinforcing agent for high-strength polymer composites, because of their fantastic mechanical strength, high electrical and thermal conductivity and high aspect ratio. Polymer/MWCNTs composites are easily molded, and the resulting shaped plastic articles have a perfect surface appearance compared with polymer composites made using usual carbon or glass fibers. Good interfacial adhesion between the MWCNTs and the polymer matrix is essential for efficient load transfer in the composite. The ultrahigh strength polymer composites demand the uniform dispersion of the MWCNTs in the polymer matrix without their aggregation and the good miscibility between MWCNT and polymer matrix. This approach can also be applied to biodegradable synthetic aliphatic polyesters such as poly(l-lactide) (PLLA), which has received a great deal of attention due to environmental concerns. In this study, PLLA was melt-compounded with MWCNTs. A high degree of dispersion of the MWCNTs in the composites was obtained by grafting PLLA onto the MWCNTs (PLLA-g-MWCNTs). After oxidizing the MWCNTs by treating them with strong acids, they were reacted with l-lactide to produce the PLLA-g-MWCNTs. The mechanical properties of the PLLA/PLLA-g-MWCNT composite were higher than those of the PLLA/MWCNT composite. The electrical conductivity of the composites was determined by measuring the volume resistivity, which is a value of the resistance expressed in a unit volume by two-probe method. The thermal diffusivity and heat capacity of composites was measured by laser flash method, and the effects of modification of the MWCNT in PLLA matrix are discussed.     

The Role of Interfacial Interactions in the Toughening of Precipitated Calcium Carbonate–Polypropylene Nanocomposites

This paper investigates the effect of the interphase properties and the interfacial interactions between matrix and filler on mechanical properties of precipitated calcium carbonate (PCC)–polypropylene nanocomposites. PCC particles were coated with stearic acid (SA). The weight ratio of SA on the particles (w _SA) ranged from 0 to 0.135 g SA/g PCC. The introduction of PCC particles resulted in an increase in stiffness and yield stress compared with the pristine polymeric matrix and, at the same time, it increased the impact resistance. The maximum improvement in the impact behaviour was achieved for the composites with w _SA =0.045 corresponding to the theoretical monolayer ratio. A decrease in interfacial interactions between monolayer coated PCCs and the matrix with respect to the uncoated particles was observed by using a semi-empirical equation developed by Pukànszky. The low degree of interfacial interactions between particulate filler and matrix allows a matrix–particle debonding phenomenon, as shown by scanning electron microscopy analysis. Extensive plastic deformations were evident as well, promoting an improvement in toughness. The thickness of the interphase between particles and matrix was evaluated by using the Shen–Li model which is based on the hypothesis of a non-homogeneous interphase. It results that the thickness increased in the order uncoated < monolayer coated < 3% SA coated ? 13.5% SA coated particles. The thinner and stronger interphase found for the composite with uncoated particles can be explained with the high interaction between matrix and filler and the consequent low mobility of the polymeric chains.     

On the mechanical behaviours of a craze in particulate–polymer composites

In polymeric composites, well-defined inclusions are incorporated into the polymer matrix to alleviate the brittleness of polymers. When a craze is initiated in such a composite, the interaction between the craze and the surrounding inclusions will greatly affect the composite’s mechanical behaviours and toughness. To the best knowledge of the authors, only little research work has been found so far on the interaction between a craze and the near-by inclusions in particulate–polymer composites. In the current study, the first time, the influences of the surrounding inclusions on the craze are investigated in particulate–polymer composites. The three-phase model is adopted to study the fracture behaviours of the craze affected by multiple inclusions. An iterative procedure is proposed to solve the stress intensity factors. Parametric studies are performed to investigate the influences of the reinforcing particle volume fraction and the shear modulus ratio on fracture behaviours of particulate–polymer composites.     

Abrasive Wear Behavior of LDPE Filled with Silane Treated Flyash Cenospheres

Lightweight, high mechanical strength insulating materials exhibiting high resistance to corrosion, solvents and abrasive wear are desired for wire and cable insulation as well as protection. Polyethylenes are generally used for such applications owing to their good electrical insulation properties and being inert to solvents at room temperature. However, their abrasion resistance is quite poor. Hence, in the present work, an attempt has been made to improve the abrasive wear resistance of low-density polyethylene (LDPE) by incorporating hollow microspheres, known as cenospheres, in the base polymer to form composites. These cenospheres are obtained from flyash particles, a thermal power plant waste, and do not tend to increase the weight of the polymer composite when used as a filler. The composites were developed by changing the weight fraction of untreated as well as silane treated cenospheres to the extent of 5 wt%. Tribological characterization of these composites was done in abrasive wear mode by varying the operating parameters, such as speed and sliding distance against silicon carbide paper. It was found that 10 wt% silane treated cenosphere filled LDPE composite showed the maximum wear resistance (～×10^?11 m³/N m) among the six composites. However, a further increase in filler concentration decreased the wear resistance. The improvement in wear resistance was supported by scanning electron microscopy and attributed to the strong interaction between silane treated cenosphere and LDPE molecules which resisted the elongation and shearing of polymer chains by the abrasive grits.     

Maintenance of highly interfacial shear strength by diblock copolymer between carbon fiber and epoxy resin in hostile environment

The environmental resistance properties of carbon fiber (CF), with various surface modifications, reinforcing epoxy resin composites have been studied by a microbond test. The results of cooling–heating cycling between ?40 and 95?°C indicate that the introduction of the flexible poly(n-butyl acrylate) (PnBA) blocks into the interface can effectively decrease the interfacial degradation rate, induced by interfacial thermal stress. After 50 cooling–heating cycles, the interfacial shear strength between CF and epoxy resin was still as high as 32.69?±?2.13?MPa. The results of hygrothermal treatment by immersing the composites in hot water show that assembly morphology of the diblock copolymer hydroxyl-terminated poly(n-butyl acrylate-b-glycidyl methacrylate) (OH-PnBA-b-GMA) at the interface can decrease the interfacial water absorption and thus increase the hygrothermal resistance of the composite. Besides, the length of PnBA block in the diblock copolymer influenced the interfacial properties of the composite in a hygrothermal environment.     

Predicting Interfacial Strengthening Behaviour of Particulate-Reinforced MMC — A Micro-mechanistic Approach

The fracture properties of particulate-reinforced metal matrix composites (MMCs) are influenced by several factors, such as particle size, inter-particle spacing and volume fraction of the reinforcement. In addition, complex microstructural mechanisms, such as precipitation hardening induced by heat treatment processing, affect the fracture toughness of MMCs. Precipitates that are formed at the particle/matrix interface region, lead to improvement of the interfacial strength, and hence enhancement of the macroscopic strength properties of the composite material. In this paper, a micro-mechanics model, based on thermodynamics principles, is proposed to determine the fracture strength of the interface at a segregated state in MMCs. This model uses energy considerations to express the fracture toughness of the interface in terms of interfacial critical strain energy release rate and elastic modulus. The interfacial fracture toughness is further expressed as a function of the macroscopic fracture toughness and mechanical properties of the composite, using a toughening mechanism model based on crack deflection and interface cracking. Mechanical testing is also performed to obtain macroscopic data, such as the fracture strength, elastic modulus and fracture toughness of the composite, which are used as input to the model. Based on the experimental data and the analysis, the interfacial strength is determined for SiC particle-reinforced aluminium matrix composites subjected to different heat treatment processing conditions.     

放电等离子烧结制备ZrB2-SiC超高温陶瓷的力学性能及氧化行为

在服役环境中,超高声速飞行器表面与空气剧烈摩擦导致温度极高。超高温陶瓷相较于一般陶瓷而言具有高熔点和良好的抗氧化烧蚀性能,是目前极具前景的热防护材料之一。采用放电等离子两步烧结工艺将ZrB2纳米粉末和SiC粉末在1700℃下制备超高温陶瓷材料ZrB2-20%SiC,通过纳米压痕微观实验、三点弯实验研究其力学性能及其在高温环境下的氧化行为,着重分析1000、1200、1400和1600℃4种不同氧化温度下ZrB2-20%SiC超高温陶瓷的氧化表面、氧化截面和氧化层厚度。结果表明:ZrB2-20%SiC超高温陶瓷的硬度为18 GPa,弹性模量为541 GPa,断裂韧性为5.7 MPa·m1/2;当氧化温度为1600℃时,超高温陶瓷内部的SiC由被动氧化转变为主动氧化,并且随着氧化温度升高,超高温陶瓷氧化层厚度与氧化温度呈正相关。     

Influence of Er:YAG laser on surface treatment of aged composite resin to repair restoration

The purpose of this study was to investigate the effect of Er:YAG laser on surface treatment to the bond strength of repaired composite resin after aged. Sixty specimens (n = 10) were made with composite resin (Z250, 3M) and thermocycled with 500 cycles, oscillating between 5 to 55°C. The specimens were randomly separated in six groups which suffered the following superficial treatments: no treatment (GI, control), wearing with diamond bur (GII), sandblasted with aluminum oxide with 27.5 μm particles (GIII) for 10 s, 200 mJ Er:YAG laser (GIV), 300 mJ Er:YAG laser (GV), and 400 mJ Er:YAG laser (GVI), with the last 3 groups under a 10 Hz frequency for 10 s. Restoration repair was done using the same composite. The shear test was done into the Universal testing machine MTS-810. Analyzing the results through ANOVA and Tukey test, no significant differences were found (p-value is 0.5120). Average values analysis showed that superficial treatment with aluminum oxide presented the highest resistance to shear repair interface (8.91MPa) while 400 mJ Er:YAG laser presented the lowest (6.76 MPa). Fracture types analysis revealed that 90% suffered cohesive fractures to GIII. The Er:YAG laser used as superficial treatment of the aged composite resin before the repair showed similar results when used diamond bur and sandblasting with aluminum oxide particles.     

A Review of the Recent Advances in Cyclic Butylene Terephthalate Technology and its Composites

Cyclic butylene terephthalate (CBT®) oligomers are a relatively new class of material and are capable of polymerizing in an entropically driven ring-opening polymerization into high-molecular-weight polymerized CBT (pCBT) in very short times, i.e., within minutes. The most important feature of CBT is its very low, water-like melt viscosity prior to polymerization which gives rise to an excellent impregnation of fibrous reinforcements in contrast to conventional, high viscous thermoplastic resins. This opens up new possibilities in the thermoplastic composite production since thermoplastic-based composites show some advantages over thermoset-based ones. Specifically, they have a higher toughness and impact strength and they can be welded, postformed, and recycled due to their thermoplastic nature. CBT has the potential to substitute thermoset matrices in fiber-reinforced composites and may solve some of the today´s recycling issues associated with thermoset-based composites. Moreover, the low melt viscosity of CBT enhances the dispersion of nano- or conductive particles and can yield superior nano- and conductive composites. This article reviews the recent advances in processing–structure–property relationship, physical and chemical modification of pCBT, as well as the preparation of fiber-reinforced pCBT composites, pCBT nanocomposites, and conductive pCBT composites.     

块体非晶合金的韧塑化

块体非晶合金因其独特的原子结构而具有许多优异的力学性能,成为近年来材料领域的研究热点之一,但是由于其在变形过程中的室温脆性和应变软化等关键问题一直制约着其实际工程应用.为解决此问题,块体非晶合金领域的研究者们提出了多种方案,包括通过在非晶合金中调控其内禀特性如弹性常数、结构不均匀性,通过外加手段改变其应力及缺陷状态,通过外加和内生的方法在非晶基体中引入晶态增强相等方式,获得了一系列力学性能优异的块体非晶合金及其复合材料.特别是利用"相变诱导塑性"(transformation-induced plasticity,TRIP)概念研制出的块体非晶合金复合材料,同时具有大的拉伸塑性和加工硬化能力.本文围绕块体非晶合金的韧塑化这个关键科学问题,对单相非晶及非晶复合材料的韧塑化方案及机理进行了综述,着重介绍了TRIP韧塑化块体非晶合金复合材料的制备、性能、组织调控及韧塑化机理等,并对此领域的未来发展进行了展望.     

Microstructure and properties of Pb(Mg1/3Nb2/3)O3–Portland cement composites

Lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN), ceramics particles was mixed with Portland Cement (PC) using a water to cement ratio of 0.50 and PMN content at 40% and 60% by weight to produce 0–3 Pb(Mg_1/3Nb_2/3)O₃–Portland cement (PMN–PC) composites. Microstructure and hydration of the composites were investigated. Calcium silicate hydrate gel can be seen surrounding the PMN particles. Dielectric constant of the composites was found to increase with PMN content. Successful poling of the composites was achieved. Interestingly, SEM micrographs of the PMN40 composite clearly showed calcium silicate hydrate gel (an essential hydration product of Portland cement) surrounding the PMN particles. In PMN60 composite, the gel can also still be seen but of less quantity. This is thought to be due to the increase in the volume ratio of the ceramics where the amount of calcium silicate hydrate gel was reduced in relation to the overall volume.     

Viscoelasticity of a polymer matrix and fracture of heat-resistant fiber composites

This paper reports on the results of investigations into the general regularities of deformation and fracture of fiber composite materials based on new heat-resistant polymer binders. Fiber composites based on these binders can find wide application in various fields of engineering. It is established that an increase in the loss modulus of the polymer matrix decreases the probability of formation of a brittle crack in the matrix at the fiber break and increases the time interval between breakages of adjacent fibers. This leads to retardation of the correlated breakage of the fibers in fiber composite materials under loading, i.e., to an increase in their strength and fracture toughness. The inference is made that the matrix of high-strength heat-resistant fiber composites with a high fracture toughness should possess not only a high elasticity (this has long been known) but also good dissipative properties over the entire temperature range of operation.     

Effects of Ca/Al ratio and extrusion process on Mg–Al–Ca alloys to produce a high toughness in-situ composite

The microstructures and tensile properties of Mg–Al₂Ca–Mg₂Ca in situ composites (Mg–17Al–8Ca, Mg–14Al–11Ca and Mg–12.5Al–12.5Ca) with different Ca/Al ratios have been studied in both as-cast and extruded conditions. The results indicated that by increasing Ca/Al ratio, new Mg₂Ca intermetallic introduces to the Al₂Ca phase in eutectic structure. Computer-aided cooling curve analysis confirmed the formation of these phases during solidification. Extrusion process not only altered the size of large bulk Al₂Ca intermetallic, but also changed the size and morphology of intermetallics in eutectic structure considerably. The results showed that with increasing Ca/Al ratio, tensile properties of cast composites changes slightly, but significant enhancement is observed after extrusion process. The strength and elongation values of Mg–12.5Al–12.5Ca (Ca/Al = 1) alloy improved from 166 MPa and 2% in as-cast condition to 465 MPa and 12% in hot-extruded condition. The reason for the improved toughness may be attributed to the formation of finer and well-dispersed distribution of hard (Al₂Ca) and ductile (Mg₂Ca) phases. It was found that hot extrusion easily deforms ductile Mg₂Ca phase in comparison with Al₂Ca phase. In as-extruded condition, there are more very fine dimples than as-casted condition because extrusion process leads to formation of fragmented tiny particles and more uniformity distribution of Al₂Ca particles.