Improvement of thermal and mechanical properties of graphite/copper composites through interfacial modification

Unidirectionally reinforced graphite/copper composites have been fabricated using a pressure infiltration casting procedure. T300 and T650 graphite fibers have been used to reinforce copper and copperchromium alloys. The effects of the chromium level in the copper matrix on the tensile strength, stiffness, and thermal expansion behavior of the composites have been evaluated through tensile and three-point bend testing, and thermal cycling. At the 0.5 wt% alloying level, chromium increases the stiffness and optimizes the thermal expansion behavior of graphite/copper composites. The longitudinal tensile strengths of these composites are above 1606 MPa, whereas the transverse tensile strengths are lower than 40 MPa due to incomplete infiltration during processing. Scanning electron microscopy analyses reveal that the unalloyed copper matrix composites experienced extensive fiber/matrix debonding under tensile loading. The addition of chromium to the copper increases the level of matrix bonding to the graphite fibers, as evidenced by observations of fractured tensile specimens. Auger electron spectroscopy analyses indicate that a chromium carbide phase present at the interface is responsible for the improved bonding.     

一种高方向灵敏度光纤F-P超声传感系统设计研究

针对光纤F-P超声传感器工作点易偏离问题,设计了基于双波长稳定技术的低细度光纤F-P传感系统,建立了双波长光纤F-P传感系统的DE算法数学模型,优化设计了一高正交精度光纤F-P传感系统,建立基于该传感器的激光超声检测系统,实验研究了该传感器探测超声信号的有效性和方向灵敏度。结果表明,该传感器可以有效检测试样中激发出的超声表面波信号。激发源与传感器轴向夹角为0°时,表面波幅值最大。随着激发源与传感器轴向夹角增大,表面波幅值降低。激发源与传感器轴线垂直时,幅值下降达80%,说明该传感器有很强的方向性。     

聚丙烯纤维对补偿收缩混凝土力学性能的影响

为了探究聚丙烯纤维对补偿收缩混凝土的强度和限制膨胀率的影响规律,通过对不同聚丙烯纤维掺量的补偿收缩混凝土与基准混凝土的对比试验,测出了不同聚丙烯纤维掺量下的补偿收缩混凝土的强度和限制膨胀率值。与基准混凝土测得的强度和限制膨胀收缩率值对比,得出了能使补偿收缩混凝土达到最大膨胀率和最大劈裂抗拉强度的聚丙烯的最优掺量为1.575 kg/m3,同时随聚丙烯掺量增加,补偿收缩混凝土的强度和限制膨胀率先增大后减小。     

Characterization of laser hardened steels by laser induced ultrasonic surface waves

Ultrasonic surface waves are suitable for the characterization of surface hardened materials. This is shown on laser hardened turbine blades. The martensitic microstructure within the surface layer of surface hardened steels has a lower surface wave propagation velocity than the annealed or normalized substrate material. Because the propagation velocity depends on the ratio of layer thickness to wavelengthd/, its measurement allows the determination of the hardening depth. If the surface wave frequency is high enough, the surface wave propagates mainly within the hardened layer. A correlation of the surface wave velocity to the surface hardness has been found. Because the variation of the surface velocity in hardened steels is small, a high measurement accuracy is necessary to obtain the interesting hardening parameters with sufficient certainty. Therefore, a measuring arrangement has been developed where laser pulses, guided by optical fibers to the surface hardened structure, generate simultaneously surface wave pulses at two different positions. The two ultrasonic pulses are received by a piezoelectric transducer. The surface wave velocity is obtained from the time delay between these pulses which is determined by the cross-correlation method. To evaluate simultaneously surface waves with different penetration depths from the same signal acquisition, digital filtering has been used in connection with the cross-correlation.     

Thermally Responsive Fibers for Versatile Thermoactivated Protective Fabrics

Smart textiles with good mechanical adaptability play an important role in personal protection, health monitoring, and aerospace applications. However, most of the reported thermally responsive polymers has long response time and poor processability, comfort, and wearability. Skin-core structures of thermally responsive fibers with multiple commercial fiber cores and temperature-responsive hydrogel skins are designed and fabricated, which exhibit rapid mechanical adaptability, good thermohardening, and thermal insulation. This universal method enables tight bonding between various commercial fiber cores and hydrogel skins via specific covalently anchored networks. At room temperature, prepared fibers show softness, flexibility, and skin compatibility similar to those of ordinary fibers. As temperature rises, smart fibers become hard, rigid, and self-supporting. The modulus of hydrogel skin increases from 304% to 30883%, showing good mechanoadaptability and impact resistance owing to the synergy between hydrophobic interactions and ionic bonding. Moreover, this synergistic effect leads to an increase in heat absorption, and fibers exhibit good thermal insulation, which reduces the contact temperature of the body surface by ≈25 °C under the external temperature of 95 °C, effectively preventing thermal burns. Notably, the active mechanoadaptability of these smart fibers using conductive fibers as cores is demonstrated. This study provides feasibility for fabricating environmentally adaptive intelligent textiles.     

Controlled chemical modification of the internal surface of photonic crystal fibers for application as biosensitive elements

Photonic crystal fibers (PCF) are one of the most promising materials for creation of constructive elements for bio-, drug and contaminant sensing based on unique optical properties of the PCF as effective nanosized optical signal collectors. In order to provide efficient and controllable binding of biomolecules, the internal surface of glass hollow core photonic crystal fibers (HC-PCF) has been chemically modified with silanol groups and functionalized with (3-aminopropyl) triethoxysilane (APTES). The shift of local maxima in the HC-PCF transmission spectrum has been selected as a signal for estimating the amount of silanol groups on the HC-PCF inner surface. The relationship between amount of silanol groups on the HC-PCF inner surface and efficiency of following APTES functionalization has been evaluated. Covalent binding of horseradish peroxidase (chosen as a model protein) on functionalized PCF inner surface has been performed successively, thus verifying the possibility of creating a biosensitive element.     

高压静电纺丝制备聚丁烯-1纤维的形貌及晶型转变

对聚丁烯-1的环己烷溶液进行高压静电纺丝制备出聚丁烯微纳米纤维,通过光学显微镜、扫描电镜、傅里叶变换红外光谱和X射线衍射等表征手段,考察了纺丝液浓度、纺丝电压、推进速率对纤维形貌的影响,并对纺丝过程及室温陈放的聚丁烯纤维的晶型转变进行了研究。结果表明,随着纺丝液浓度和推进速率的增大,可以得到尺寸均匀的纤维,直径也随之变大;纺丝电压增大,纤维直径减小,但纤维直径分布均匀性变差。初生聚丁烯-1纺丝纤维膜的晶型为I型和II型,随着溶剂的挥发和时间延长,晶型II逐渐转变为晶型I,溶液涂覆膜初生晶型为晶型III和晶型I'。     

激光与碳纤维相互作用的研究现状及发展趋势

由于高比强度、比模量等优良特性,碳纤维成为轻量化制造业的关键原材料之一,拥有广阔的发展潜力,然而高成本、低产率及工艺缺陷等弊端限制了其发展。激光技术的引入给碳纤维的加工制备提供了新的方向。概述了激光与碳纤维相互作用的最新研究进展,详细介绍了激光在加工、制备碳纤维各工艺过程中的作用机制,总结了激光技术在碳纤维复合材料生产加工领域的研究进展,最后分析和展望了激光辅助加工制备碳纤维过程目前仍存在的一些问题及可能的发展方向、应用前景。     

A Flexible Conformal Piezoresistive Sensor Based on Electrospinning for Deformation Monitoring of Carbon Fiber-Reinforced Polymer

Carbon fiber-reinforced polymer (CFRP) materials are widely applied in various areas as key structure components. The structural health monitoring of the CFRP components is crucial to prevent catastrophic failure. However, the nonplane surfaces of CFRP components hinder the attaching of monitoring sensors with hard substrates. Therefore, the substrate conditions for sensor preparation are mainly considered in this study. To adapt the proposed sensors to the curved substrate, including nondevelopable surfaces, electrospinning method is used to prepare conformal piezoresistive fiber films, in which polymethyl methacrylate is served as the matrix and carbon nanotubes are utilized as the conductive filler. The piezoresistive fibers covered on CFRP substrates have a gauge factor up to 207.95 and can response to the strain less than 0.05%. Moreover, the sensor also has high durability and the ability to follow the dynamic excitation signals with as high as 50 Hz.