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201.
Experimental revelation ofsuperblunting along plane strain predominant crack tip segment is reported here for modified polyproplene. As elucidated by a heuristic
model of progressive circumferential cold-draw, the formation of superblunting crack tip depends critically on the ratio between
the cold-draw propagation speed and the loading speed, and contributes significantly to the material toughening, especially
for the improvement in impact toughness. Detailed numerical calculations are conducted based on a hyperelastic-viscoplastic
and anisotropic damage constitutive model at finite deformation. The simulated results recapitulate the essential features
of crack tip superblunting.
The project supported by the National Natural Science Foundation of China 相似文献
202.
用云纹干涉法研究了带直通切口的Ce TZP(Tetragonal ZirconiaPolycrystal)和Ce TZP/Al2O3层状复合材料三点弯曲梁的相变过程.实验发现1600°C/3h烧结12%molCeO2稳定的Ce TZP在室温下就具有强烈的自催化效应,直通切口前缘的相变区呈树枝状,Ce TZP/Al2O3层状复合材料的自催化相变被Al2O3层抑制,切口前缘的相变区变短,且相变区的覆盖面积减小.文中最后对Al2O3层改变Ce TZP相变区及力学性能的原因进行了讨论. 相似文献
203.
In this paper, two and three-dimensional clustering models are developed to characterize the effect of nano-particle clustering
on toughening of nanocomposite ceramics. It is found that crack pinning toughens the nano-composite ceramics because a higher
stress intensity factor is needed for crack to propagate around or to pull-out the nano-particle. The nano-particle along
the grain boundary steers the crack into the matrix grain due to the strong cohesion between the nanoparticle and the matrix.
Since the fracture resistance of the grain boundary is lower than that of the grain lattice, the higher the probability of
transgranular fracture induced by nano-particles, the tougher is the nano-composite. However, both crack pinning and transgranular
fracture are affected by nano-particle clustering. Nanoparticle clustering, which increases with increasing volume fraction
of nano-particles, leads to reduction of both the strength and toughness of the nano-composite ceramics. The larger the size
of the clustered particle, and the more defects it contains, the easier it is for the crack to pass through the clustered
particle, which means that the nano-particle clustering can reduce toughening induced by crack pinning and transgranular fracture.
The theoretical prediction, based on the combination of the three mechanisms of nano-particles, is in agreement with the experimental
data.
The project supported by the National Natural Science Foundation of China (19891180) and the Research Grants Council of the
HKSAR, China(HKU7081/00E) 相似文献
204.
Based on a constitutive law which includes the shear components of transformation plasticity, the asymptotic solutions to near-tip fields of plane-strain mode I steadity propagating cracks in transformed ceramics are obtained for the case of linear isotropic hardening. The stress singularity, the distributions of stresses and velocities at the crack tip are determined for various material parameters. The factors influencing the near-tip fields are discussed in detail.Project supported by the National Natural Science Foundation of China 相似文献
205.
Yongcheng Liu Tao Zhou Zhengguang Chen Lin Li Yanhui Zhan Aiming Zhang Feiwei Liu 《先进技术聚合物》2014,25(7):760-768
In this study, the unique crystallization behavior of poly(ethylene oxide) (PEO) in polyoxymethylene (POM)/PEO crystalline/crystalline blends was examined in detail. This study was the first to report the typical fractionated crystallization of PEO in POM/PEO blends when PEO is fewer than 30 wt.%. The delayed crystallization temperature of PEO was confirmed at about 5°C to 14°C by using differential scanning calorimetry and perturbation–correlation moving‐window 2D correlation IR spectroscopy. Wide‐angle X‐ray diffraction indicates that no new crystal structures or co‐crystals were generated in POM/PEO. The statistical calculations of scanning electron microscopy photos show that the average diameter of PEO particles is 0.227 µm to 1.235 µm and that the number of small particles is as many as 109 magnitudes per cm3. Theory analysis establishes that the delayed crystallization of PEO is a heterogeneous nucleation process and not a homogeneous nucleation process. A significant toughening effect of PEO to POM was also observed. The impact strength of POM/PEO acquires a maximum of 10.5 kJ/m2 when PEO content is 5%. The impact strength of the blend increases by 78.0% compared with pure POM. To improve the toughening effect, the best particle size is established between 0.352 and 0.718 µm, with a PEO particle spacing of 0.351 µm to 0.323 µm. The number of corresponding particles was 0.887 × 109 per cm3 to 3.240 × 109 per cm3. A PEO toughening model for POM was proposed to provide a new and effective way to solve the problem of POM toughening. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
206.
根据短纤维在层间杂乱分布和接近裂纹表面的特点,考虑基体剥落和纤维拉出耦合,本文建立了一个层间短纤维桥联模型,分析短纤维的层间增韧机理和主要影响因素。计算结果表明,纤维增强树脂层板在层间加入少量的Kevlar短纤维时,裂纹张开位移导致短纤维从基体中剥离和拉出,在纤维相互干扰下,拉出过程中产生大的能量耗散,从而明显地提高层间断裂韧性。纤维界面性质对△G1c有重要影响,纤维杂乱分布引起的相互干扰及纤维初始弯曲,使层间断裂韧性显著增加。比较表明,△G1c的理论预测与实验结果相符合。 相似文献
207.
208.
增韧环氧树脂的微结构和力学性能的正电子湮没 总被引:2,自引:0,他引:2
用正电子湮没方法(PALS)和动态力学分析(DMA)方法研究了增韧剂和温度对环氧树脂的自由体积和力学性能的影响.根据正电子素(o-Ps)湮没寿命τ3随温度的变化,玻璃化转变温度Tg和次级转变温度Tβ被确定.实验结果表明,在稀释环氧树脂基体中加入增韧剂会使样品中产生较强界面相互作用,并且明显地改变了材料的结构转变温度Tg和Tβ,使得增韧样品比稀释样品具有更高的玻璃化转变温度Tg.一个很有意义的发现是,低温下力学性能的改变明显地大于室温下力学性能的改变.文中从原子尺度自由体积特性和界面相互作用的角度探讨了温度对样品力学性能影响的机理. 相似文献
209.
β成核剂改性聚丙烯的研究 总被引:1,自引:0,他引:1
研究了β晶型成核剂对聚丙烯力学性能和热学性能的影响,并对其进行了DSC、正交偏光显微镜和电镜观察.研究表明:添加β成核剂后,聚丙烯晶型由α晶型向β晶型转变,韧性大大增强.β成核剂用量在0.2%时,冲击强度比未加成核剂时提高了3倍左右,其拉伸强度几乎没有变化,其软化点提高了15~20℃. 相似文献
210.
钇对陶瓷刀具材料Al2O3/TiCN的强韧化效应 总被引:6,自引:1,他引:5
在已 研制的含烯土Al2O3/TiCN陶瓷刀具材料的基础上,采用SEM,TEM和能谱分析等方法探讨了Y的强韧化效应。稀土增强Al2O3/TiCN陶瓷刀具材料力学性能改善的原因在于,Y的添加能在一定程度上积聚杂质,W,Fe和Cr等,从而起到清洁界面、提高界面结合强度的作用。 相似文献