Deformation mechanism maps for superplastic materials

(i) sufficient experimental results are now available for the construction of deformation maps for two superplastic materials, Zn-22% Al and Pb-62% Sn, and (ii) when plotted in the form of grain size versus stress, the maps for these two alloys provide strong evidence that superplasticity only occurs at grain sizes sufficiently small that a stable subgrain structure is not formed during deformation.     

Biomimetic nanostructured coatings on nano-grained/ultrafine-grained substrate: Microstructure, surface adhesion strength, and biosolubility

We describe here the structural morphology, nucleation and growth, surface adhesion response and biosolubility in simulated physiological fluid of nanohydroxyapatite (nHA)-based coatings (nHA, chitosan-nHA, collagen-nHA) on nano-grained (NG)/ultrafine-grained (UFG) 316L austenitic stainless steel bulk substrate. The NG/UFG stainless steel was processed by a novel procedure involving controlled phase reversion of strain-induced martensite. Electron microscopy studies indicated that the morphology of nHA on NG/UFG stainless steel is characterized by a vein-type interconnected structure consisting of fibrils that closely mimics the fibrous structure present as part of the hierarchical structure of the bone. Interestingly, the dimensions of the vein-type interconnected structure were similar to the grain size of NG/UFG stainless steel substrate. This structural morphology was retained in crystallized chitosan-nHA coating, but was modified when collagen is codeposited with nHA. The mechanisms of deposition are discussed based on the structural characteristics of coatings. Adhesion response of coating as determined by scratching tests suggested superior adhesion strength of nHA coating on NG/UFG substrate as compared to that on CG substrate and is attributed to grain size effect and wettability of the substrate.     

Comparison of plasticity models for tantalum and a modification of the PTW model for wide ranges of strain,strain rate,and temperature

Four well-known constitutive models for plastic deformation of materials, i.e., Johnson–Cook (JC), Zerilli–Armstrong (ZA), Voyiadjis and Abed (VA), and Preston–Tonks–Wallace (PTW), have been compared with reference to existing deformation data of tantalum in wide ranges of strain, strain rate, and temperature. All of these models reasonably describe the flow stress and the strain-hardening behavior only in the certain ranges of strain, strain rate, and temperature for which the models were developed. The PTW model with appropriate parameters most effectively describes the effects of strain rate and temperature in a wider range, except for strain hardening. The strain-hardening term of PTW was thus modified in the current work and the modified PTW demonstrated very good prediction for the constitutive behavior of tantalum in wide ranges of strain, strain rate, and temperature.     

Modeling for fracture in materials under long-term static creep loading and neutron irradiation. Part 2. Prediction of creep rupture strength for austenitic materials

We present some results of prediction of creep rupture strength and plasticity for austenitic materials prior to and after irradiation with variable neutron flux rates, based on physicomechanical model as outlined in Part 1. The calculated results are compared with the available experimental data. __________ Translated from Problemy Prochnosti, No. 5, pp. 5–15, September–October, 2006.     

块体纳米晶Al-Zn-Mg-Cu合金的微区力学性能和变形机制

研究了块体纳米晶Al-10Zn-2.8Mg-118Cu合金热处理前后的微区力学性能和变形机制,结果表明:块体纳米晶Al-10Zn-2.8Mg-1.8Cu合金经T6处理后杨氏模量没有明显的变化,硬度明显提高;在SPS试样中可观察到明显的室温蠕变和剪切带,随着应变速率的增加,室温蠕变越来越明显,但是剪切带越来越不明显;而在T6态试样中很难观察到室温蠕变和剪切带。T6处理改变了第二相粒子的形貌和分布,是产生这一现象的原因。     

Intrinsic ductility for structural materials as a function of stress and temperature

Abstract

In recent years, a method has been developed to measure current creep strength at nearly constant structure in a high precision stress relaxation test (SRT), covering at least five decades in creep rate in a one day test. Results have been reported on a wide range of metallic alloys, polymers, composites and ceramics. In the present paper it is shown that these same data can be used to determine a measure of intrinsic ductility over the same range of stress, using results on a low alloy Cr–Mo–V steel. This is based on an experimental and theoretical correlation between elongation at failure and strain rate sensitivity, m. This refined SRT test can now be used to evaluate both the intrinsic creep strength and the intrinsic ductility as a function of stress in a single short-time test. The test can detect embrittling phenomena at very low creep rates as a function of temperature. This measure of ductility may be used directly in engineering design and remaining life assessment.     

多孔材料抑制瓦斯爆炸传播的实验及机理

利用自行设计加工的断面为30cm×30cm方形爆炸实验管道,对不同参数的金属丝网、泡沫陶瓷材料和多孔泡沫铁镍金属的抑爆效果分别进行了实验研究,结合材料特点,分析了其抑爆机理。实验结果表明,金属丝网、泡沫陶瓷和多孔泡沫铁镍金属对瓦斯爆炸传播均有一定抑制作用,多孔泡沫铁镍金属衰压和阻火效果优于金属丝网和泡沫陶瓷,材料的损坏程度明显降低,对火焰衰减效果增强;测点4,多孔泡沫铁镍金属相比40目40层金属丝网对最大火焰温度的衰减率提高了43.8%,相比Al2O3 7cm大孔泡沫陶瓷提高了34.5%。测点7,多孔泡沫铁镍金属相比40目40层金属丝网体对爆炸超压的衰减率提高了29.9%,相比SiC 5cm大孔泡沫陶瓷提高了22.4%。     

Discoloration mechanism,structures and recent applications of thermochromic materials via different methods: A review

Thermochromic material is a kind of smart material whose color will vary as the result of the phase transition caused by the temperature change. The characteristics of thermochromic materials are the memory functions to the temperature, having great potential applications in aerospace, military, anti-counterfeiting technology, construction and other fields. In recent years, many kinds of thermochromic materials have been prepared by different methods and their discoloration mechanisms are various according to published literatures. In this paper, the classification, discoloration mechanism, preparation methods, application fields and development trend of thermochromic materials are reviewed.     

聚合物梯度材料黏弹性断裂的双控制参数

针对组分材料体积分数任意分布的聚合物功能梯度材料,研究其在蠕变加载条件下Ⅰ型裂纹应力强度因子（SIFs）和应变能释放率的时间相依特征。由Mori-Tanaka方法预测等效松弛模量,在Laplace变换域中采用梯度有限元法和虚拟裂纹闭合方法计算断裂参数,由数值逆变换得到物理空间的对应量。分析边裂纹平行于梯度方向的聚合物功能梯度板条,分别考虑均匀拉伸和三点弯曲蠕变加载。结果表明,聚合物梯度材料应变能释放率随时间增加,其增大的程度与黏弹性组分材料体积分数正相关;材料的非均匀黏弹性性质产生应力重新分布,导致裂纹尖端应力场强度随时间变化,当裂纹位于黏弹性材料含量较低的一边时,应力强度因子随时间增加,反之,随时间减小。而且,材料的应力强度因子与时间相依的变化范围和体积分数分布以及加载方式有关,当体积分数接近线性分布时,变化最明显,三点弯曲比均匀拉伸的变化大。SIFs随时间的延长增加或减小、加剧或减轻裂纹尖端部位的“衰坏”,表明黏弹性功能梯度裂纹体的延迟失稳需要联合采用应力强度因子与应变能释放率作为双控制参数。     

Multi-step shear banding for bulk metallic glasses at ambient and cryogenic temperatures

Analysis of energy dissipation during shear-banding aids to understand plastic deformations of bulk metallic glasses (BMGs). For Zr₅₅Al₁₀Ni₅Cu₃₀ BMGs at 298 K, multi-step shearing is proposed, and the thermal energy during serrations cannot result in a temperature rise (ΔT) higher than T_m. At 77 K, N-step shearing is supposed. When N is in the range of 24–47, it is reasonable to deduce the resulting temperature from 0.8T_g to T_m, accompanied by a continuous plastic deformation.     

偏离〈001〉取向15°的三种镍基单晶高温合金试样的中温蠕变变形行为

研究了一种偏离<001>取向15^o的镍基单晶高温合金的中温蠕变(760℃/793 MPa)性能和变形组织。结果表明：取向靠近<001>-<101>边界合金的蠕变寿命最长,而取向靠近<001>-<111>边界合金的蠕变寿命最短。虽然三种试样取向偏离<001>的夹角都约为15^o,但是其微观变形组织明显不同。取向靠近<001>-<101>边界试样的变形主要受控于{111}<110>滑移系,而取向靠近<001>-<111>边界试样变形主要受控于{111}<112>滑移系。     

The quest for stiff,strong and tough hybrid materials: an exhaustive exploration

How to arrange soft materials with strong but brittle reinforcements to achieve attractive combinations of stiffness, strength and toughness is an ongoing and fascinating question in engineering and biological materials science. Recent advances in topology optimization and bioinspiration have brought interesting answers to this question, but they provide only small windows into the vast design space associated with this problem. Here, we take a more global approach in which we assess the mechanical performance of thousands of possible microstructures. This exhaustive exploration gives a global picture of structure–property relationships and guarantees that global optima can be found. Landscapes of optimum solutions for different combinations of desired properties can also be created, revealing the robustness of each of the solutions. Interestingly, while some of the major hybrid designs used in engineering are absent from the set of solutions, the microstructures emerging from this process are reminiscent of materials, such as bone, nacre or spider silk.     

Modelling and lifing of structural materials for future aeroengine components

This paper reports on some of the major research and development activities at the SMC into materials modelling of existing advanced high strength superalloys and the work in progress to understand the step change materials which will have to be introduced into future engines to meet the perceived performance requirements. These studies are aimed at developing appropriate lifing methodologies and ensuring safe service usage of these materials. Lifing models for dwell sensitive titanium alloys, powder metallurgy materials, single crystal alloys, metal matrix composites and intermetallic alloys are considered.     

Sol-Gel法制备纳米TiO2的原料配比和胶凝过程机理探研

以钛醇盐为前驱物，不同的螯合剂、溶剂和催化剂为原料，用sol-gel法制备纳米TiO2凝胶。通过改变原料配比和实验条件对sol-gel制备过程中的作用机理进行探讨研究，从而获得制备纳米TiO2凝胶的最佳原料配比、工艺过程和控制条件。     

A fatigue life prediction method for coke drum base,weld, and HAZ materials from tensile properties

The importance of material fatigue information in design has been well recognized. There are a few existing fatigue life prediction methods based on materials tensile properties. Some of these fatigue life prediction methods can be successfully applied for non-heat affected materials. However, industrial components, such as pressure vessel and pipelines are commonly constructed by welding parts together. The fatigue lives of welded section and its surrounding material could be greatly affected by the welding process. Therefore, it is beneficial to develop a fatigue life prediction model for the weld and surrounding heat affected zone (HAZ) materials based on their tensile testing data. In this paper, fatigue lives of base material and its weld and HAZ materials for constructing coke drums are studied. Mechanical properties are first obtained from the tensile tests. Then, fully-reversed strain-controlled fatigue tests were performed. It is found that the fatigue life of pure base material is roughly twice of the weld and four time of the HAZ at the same strain amplitude. Four-point correlation (FPC) method by Manson can reasonably predict the life of base material. However, it over-predicts the lives of weld and HAZ. By introducing two reduction factors R_plastic and R_elastic for the weld and HAZ material respectively into the FPC method, the over-prediction can be rectified. Therefore, the proposed modified FPC method could be applied in predicting fatigue lives of weld and HAZ materials.     

Development of a simple and practical method for estimating the liquid absorption of pharmaceutical porous materials using a capillary rise technique

Porous materials are attractive substances for designing pharmaceutical particulates. However, understanding the behavior of liquid absorption into the intra-pores and interstices of porous carrier particles is important to effectively manufacture active pharmaceutical ingredients (APIs) using these carriers. In this study, we established a simple and practical method for evaluating the liquid absorption behavior of porous carriers using force tensiometry and a capillary rise technique. Different-sized tablets of porous materials were prepared and evaluated by this method using various solvents to estimate liquid absorption into the intra-particle pores and interstices of the particles. The amount of liquid trapped in the interstices of the particles decreased with decreasing tablet volume, after which the amount of liquid in the intra-particle pores could be estimated. Finally, API-loaded particles were prepared by absorbing the API solution into porous carriers based on the intra-capacity revealed above. No free API was found on the surface of the prepared particles, as it was well absorbed into the intra-particle pores. Collectively, this tensiometer method using different-sized tablets of porous materials appears to be a promising technique for evaluating the liquid absorption characteristics of porous pharmaceutical materials.     

基于DMM加工图的Ti-6Al-2Zr-1Mo-1V合金热塑性变形参数优化识别

通过Ti-6Al-2Zr-1Mo-1V（TA15）合金多组试样热物理模拟压缩实验获得温度1073～1323K、应变速率0.01～10s-1下的真实应力-应变数据,以此作为计算应变速率敏感指数m、功率耗散系数η、失稳判据ξ三重指标的底层材料模型。以一组3D曲面形式揭示了应力、应变速率、温度、应变量的共同作用诱导的多种变形机制的转化及同时存在所引起的应变速率敏感系数m的剧烈响应,并通过m值的正负初步识别变形稳定区和失稳区。进一步绘制能量耗散图并识别出η值为负的不稳定变形区,以及η值为正的稳态变形区。在此基础上最后通过失稳判据分布图识别出ξ〉0的稳定变形区、ξ≤0的失稳变形区。最后将不同应变下的功率耗散图和失稳图叠加以构造最终所需的含应变影响的系列加工图。综合识别后,具有较高m值水平、较高η值水平、较高ξ值水平的稳定变形参数区间为优先推荐,具有负m值水平、负η值水平、负ξ值水平的失稳变形参数区间为避免推荐。