Role of microstructure in the aging-related deterioration of the toughness of human cortical bone

The aging-related deterioration of the fracture properties of bone, coupled with higher life expectancy, is responsible for increasing incidence of bone fracture in the elderly; consequently, an understanding of how these fracture properties degrade with age is essential. In this study, ex vivo fracture experiments have been performed to quantitatively assess the effect of age on human cortical bone in the proximal–distal orientation, i.e., longitudinally along the osteons. Because cortical bone exhibits rising crack-growth resistance with crack extension, the toughness is evaluated in terms of resistance-curve (R-curve) behavior, measured for bone taken from wide range of age groups (34–99 years). Using this approach, both the crack-initiation and crack-growth toughness are determined and are found to deteriorate with age; the initiation toughness decreases some 40% over six decades from 40 to 100 years, while the growth toughness is effectively eliminated over the same age range. The reduction in crack-growth toughness is considered to be associated primarily with a degradation in the degree of extrinsic toughening, in particular, involving crack bridging in the wake of the crack. An examination of the micro-/nano-structural changes accompanying the process of aging, using optical microscopy, X-ray tomography, nanoindentation and Raman spectroscopy, is shown to support such observations.     

Effect of cryo-induced microcracks on microindentation of hydrated cortical bone tissue

Microcracks accumulate in cortical bone tissue as a consequence of everyday cyclic loading. However, it remains unclear to what extent microdamage accumulation contributes to an increase in fracture risk. A cryo-preparation technique was applied to induce microcracks in cortical bone tissue. Microcracks with lengths up to approximately 20 μm, which were initiated mainly on the boundaries of haversian canals, were observed with cryo-scanning electron microscopy. A microindentation technique was applied to study the mechanical loading effect on the microcracked hydrated bone tissue. The microindentation patterns were section-scanned using confocal laser scanning microscopy to understand the deformation and bone damage mechanisms made by mechanical loading. The results show that there was no significant difference with respect to microhardness between the original and microcracked hydrated cortical bone tissues (ANOVA, p > 0.05). The cryo-induced microcracks in the bone tissue were not propagated further under the mechanical loads applied. The deformation mechanism of the microcracked cortical bone tissue was plastic deformation, not brittle fracture.     

老化对改性沥青微观结构及疲劳性能的影响

为了研究老化对改性沥青微观结构及疲劳性能的影响,通过沥青常规指标测试试验、动态剪切流变（DSR）试验和AFM测试试验,从宏细观角度分析了老化前后苯乙烯-丁二烯-苯乙烯三嵌段共聚物（SBS）改性沥青和胶粉改性沥青的针入度、延度和软化点及疲劳性能、微观结构的变化情况。结果表明：随着老化程度的加深,两种改性沥青的稠度、硬度增加,高温性能得到改善,而温度敏感性变低,低温抗裂性能变差。综合分析针入度比、延度比和软化点比得出胶粉改性沥青的抗老化性能优于SBS改性沥青;随温度的降低、频率的增大和老化程度的加深,两种改性沥青的抗疲劳性能变差;微观结构观测结果显示,SBS改性沥青具有"蜂型结构",老化后"蜂型结构"的体积增大、高度增加、数量减少;胶粉改性沥青没有"蜂型结构",胶粉颗粒与沥青在共混共融过程中发生溶胀、脱硫和降解等行为会影响沥青中"蜂型结构"的形成;老化前后胶粉改性沥青表面形貌粗糙度和高度变化不大;胶粉改性沥青的抗疲劳、抗老化和高温性能总体优于SBS改性沥青。     

Nano- and micromechanical properties of hierarchical biological materials and tissues

The mechanical properties of biological materials have been the focal point of extensive studies over the past decades, leading to formation of a new research field that intimately connects biology, chemistry and materials science. Significant advances have been made in many disciplines and research areas, ranging throughout a variety of material scales, from atomistic, molecular up to continuum scales. Experimental studies are now carried out with molecular precision, including investigations of how molecular defects such as protein mutations or protein knockout influence larger length- and time-scales. Simulation studies of biological materials now range from electronic structure calculations of DNA, molecular simulations of proteins and biomolecules like actin and tubulin to continuum theories of bone and collagenous tissues. The integration of predictive numerical studies with experimental methods represents a new frontier in materials research. The field is at a turning point when major breakthroughs in the understanding, synthesis, control and analysis of complex biological systems emerge. Here we provide a brief perspective of the state of this field and outline new research directions.     

PVB对聚氨酯共混杂化膜微孔结构及性能的影响

选择不同黏度的聚乙烯醇羧丁醛(PVB)树脂,分别添加到聚氨酯(PU)/SiO2体系中,利用浸没沉淀相转化法制备了PU/PVB/SiO2共混杂化膜.分别对PU共混杂化体系的DMA曲线、膜性能进行了测试,并用SEM观察了膜试样的断面结构.结果表明:PVB与PU共混后,该体系的耐非溶剂性变强;PU/PVB为基本不相容体系,但加入PVB能明显加快体系的分相速度,促使在PU/PVB之间产生界面微孔;SEM膜断面照片也显示了分相速度加快而成型出较大的指状孔.PU共混杂化膜的水通量和截留率明显提高,在保持较高通量情形下,截留率可高达85%.     

二级界面对水泥基材料孔结构和性能的影响

将粉煤灰、硅灰和纳米纤维材料--活性NR粉应用于水泥基材料中，依据最大密实度理论和微粒级配数学模型设计出水泥基材料，研究了水泥基材料中二级界面对其性能的影响．结果表明，加入活性NR粉纳米纤维矿物可改善体系的颗粒级配和水泥基材料中二级界面的显微结构，提高均匀性，降低孔隙率，优化体系的孔结构．改善二级界面的显微结构可降低体系的总比孔容，提高球形孔隙体积率，降低体系的最可几孔径，优化硬化浆体的孔结构以及提高体系的内部拉应力，提高水泥基材料的抗弯强度．     

热处理温度对PAN基炭纤维结构的影响

利用SEM观察了3种PAN基炭纤维（TX－63、T300、T700）热处理前和经不同温度热处理后的表面形貌，并测试了其石墨化度、Lc和d002值，以研究热处理温度对炭纤维表面和内部微观结构的影响。结果表明：TX－3、T300炭纤维表面本身有不规则沟槽、凸起和缺陷等，T700炭纤维表面比较圆滑，随着热处理温度升高，PAN基炭纤维的表面形貌发生明显的变化，尤其是2700℃处理后炭纤维表面的褶皱相对较浅而小；石墨化度与Lc随热处理温度升高而增大，d002值则呈减小趋势，说明热处理温度对炭纤维的表面和内部结构有显著影响。     

Effect of microstructure and physical parameters of hollow glass microsphere on insulation performance

Hollow glass microsphere (HGM) is a special type of inorganic functional powder with wide applications. HGM can be applied in the insulation area as fillers owing to the hollow structure that is not conductive to the transfer of heat. The mechanism of heat transfer in HGM is analyzed and the thermal conductivity is proved to be the main heat transfer. Then a simple model comprised of continuous solid phase and independent gas phase is proposed to study the methods for decreasing the thermal conductivity of the filled system through the methods of reducing the density of HGM or increasing the stacking coefficient of HGM. This work provides actual guidance for the design and controlled preparation of composite materials with hollow glass microspheres as functional filler.     

大气下空气滑膜阻尼对微机械惯性传感器的影响

 设计并制作了一种可在大气下工作的栅结构电容式微机械加速度传感器,并对其空气滑膜阻尼特性进行了研究．测试结果表明该种结构机械品质因子Q值在大气压下能达到504．这种具有高Q值的栅形电容检测结构可以应用到微机械陀螺的检测模式,它无需真空封装,可以在大气环境下工作,且灵敏度提高．对陀螺原型的测试结构表明,其在大气下检测模态的Q值可以达到715。     

Effect of bioactive glass granules and polytetrafluoroethylene membrane on repair of cortical bone defect

The effect of bioactive glass (BG) granules and nonresorbable polytetrafluoroethylene (PTFE) membrane on the repair of cortical bone defects was studied. Monocortical holes (diameter 3.0 mm) were drilled in rabbit tibia. Sixteen holes were filled with BG granules (diameter 630–800 m). Twelve holes were left empty and covered with PTFE membrane. No material was used at ten control holes. All experiment areas were covered with periosteum attached to the soft tissue flap. Histomorphometric evaluation of resection specimens showed that new bone and glass particles formed a continuous bridge in the BG group at the upper part of the hole, occupying 73.6% and 61.7% of the defect at 6 and 12 weeks, respectively. If only the amount of bone but not glass particles was included in the measurements the corresponding figures were 31.4% and 41.5%. The bone repair in the PTFE group was 12.1% and 11.3% and in the control group 25.1% and 23.3% at 6 and 12 weeks, respectively. The results indicate that BG granules improve repair of cortical bone defects and PTFE membrane seems to impair bone formation in these defects.     

热交换器表面Ni-P镀层工艺对组织性能的影响

研究利用电子探针、显微硬度仪、X射线衍射手段对不同工艺下的化学镀Ni-P镀层进行了研究,结果表明了镀层的化学成分仅与主盐与还原剂的浓度有关,与络合剂的数量无关,但络合剂的数量可以改变镀层的微观形貌及镀速,以及影响镀层的结晶形态,随络合剂数量的增加镀层中纳米相的比例增加,在微观硬度上表现为增加.     

Analysis of the mechanical performance of a cardiovascular stent design based on micromechanical modelling

Stents are very commonly used in the treatment of coronary heart disease. They are permanent vascular support structures that offer a preferred alternative to bypass surgery in certain situations. The purpose of this work is to examine the mechanical behaviour of a stainless steel balloon expandable stent design using computational micromechanics in the context of the finite element method. Deployment and cardiac pulsing loading conditions are considered. Classical phenomenological plasticity theory (J₂ flow theory) and physically based crystal plasticity theory are used to describe the stent material behaviour. Parametric studies are carried out using both constitutive theories with a view to determining important stent deployment characteristics such as recoil and foreshortening. Comparisons of the results obtained using both theories illustrate differences, with the crystal plasticity theory models showing closer agreement to published performance data. The implications of this for stent design are discussed.     

The effects of bovine trabecular bone matrix particulates on cortical bone repair

This paper reports the effects of a synthetic bone substitute and bone allograft on cortical bone repair in an experimental model. To test the hypothesis that bovine trabecular bone matrix, BBM, can enhance the repair rate of cortical bone, osteotomies were created in the rabbit fibula and filled with either allograft or BBM particulates or left empty as controls. At five weeks post-surgery, mechanical tests and histological evaluations were performed. No significant differences were observed in the mechanical properties of the healing bone in the three animal groups (n=6). Histologically, the medullary cavity was obstructed and the cross-sectional area ratio of the osteotomies to intact bone was approximately 3 : 1. Highly significant area differences were observed between the intact bone group and both the BBM and the allograft groups . At the junction between the original bone and the newly formed bone, both woven and lamellar bone microstructures were prevalent. However, in the BBM filled defects, the woven bone microstructure was not ostentatious. It is concluded that failure to demonstrate significantly differences between the treatments were due to the small sample sizes and or the efficacy of the tensile analysis.     

均匀化退火后冷却条件对Al-Cu合金组织性能影响

为优化铝合金均匀化退火后的冷却工艺参数,采用动态电阻法、扫描电镜、透射电镜观察、能谱分析和硬度测试等方法,研究了均匀化处理后的冷却条件对Al-4%Cu合金组织性能的影响.获得的电阻率-温度曲线与材料的脱溶行为有良好的相关性.随着均匀化处理后冷却速率的降低,实验合金在冷却过程中会依次析出平衡相θ、亚稳相θ'和θ″.绘制了实验合金的CCT图,确定的脱溶敏感温度区间为500~300℃.选用合适的冷却工艺可以改善合金的组织性能,冷却时间超过1 000 min,合金有较低的硬度和电阻率.当实验合金均匀化后冷却至室温的时间处于19.4~184.1 min时会析出θ″相,导致硬度和电阻率上升,不利于后续的塑性加工,应该尽量避免.     

A micromechanical elastic property study of trabecular bone in the human mandible

Micromechanical properties of human mandibular trabecular bone, with particular interest to any site differences were investigated. A mandible was harvested from a 66 year-old female cadaver free from bone disease. It was embedded in PMMA, cut into 2mm sections and polished. Micromechanical property measurements were obtained using the UH3 Scanning Acoustic Microscope (SAM) (Olympus Co., Tokyo, Japan) at 400MHz in the burst mode. 6 vertical slices from the right and 6 horizontal slices from the left were chosen. In each of the 12 samples, 3 points were measured; first in the center, the other 2 from the margins. Data were analyzed statistically by SPSS (SPSS, Inc.) using Student’s t-test. The average value of reflection coefficient r is 0.58±0.079 with the range from 0.46 to 0.64; E=25.0±5.64 GPa. There is no significant difference in properties in the osteonal direction of related cortical bone and those found between the marginal area and center areas. The average value of r from the right side, 0.60±0.07, is statistically higher than the average value of from the left side, 0.56±0.07. Micromechanical properties of both mandibular trabecular and cortical bone have almost the same values.     

乳化炸药微观结构对其宏观性能的影响分析

分析乳化炸药内相粒子大小和分布、界面膜、油膜、第三相物质(敏化剂)对其爆炸性能、稳定性、流变性或黏度等宏观性能的影响,建立了微观结构与宏观性能的关联关系,对一些常见现象进行了解释。分析认为,乳化炸药内相粒子的大小与分布,主要取决于机械作用强度和乳化剂的种类和用量两个方面。在相同的配方和工艺条件下,乳化炸药的内相粒子越小,粒径分布越窄,其稳定性和爆炸性能就越好,黏度较大。内相粒子间界面膜和油膜既与内相粒子密切相关,也对乳化炸药的黏度、流动性和稳定性有重要作用。依据热点理论,当气泡或者气泡载体的尺寸在有效范围之内,且分布均匀时,则形成热点的时间接近,有利于爆炸反应的快速激发和传递,宏观上表现为乳化炸药爆轰感度、爆速和猛度等较大。     

乳化炸药微观结构对其宏观性能的影响分析

分析乳化炸药内相粒子大小和分布、界面膜、油膜、第三相物质(敏化剂)对其爆炸性能、稳定性、流变性或黏度等宏观性能的影响,建立了微观结构与宏观性能的关联关系,对一些常见现象进行了解释。分析认为,乳化炸药内相粒子的大小与分布,主要取决于机械作用强度和乳化剂的种类和用量两个方面。在相同的配方和工艺条件下,乳化炸药的内相粒子越小,粒径分布越窄,其稳定性和爆炸性能就越好,黏度较大。内相粒子间界面膜和油膜既与内相粒子密切相关,也对乳化炸药的黏度、流动性和稳定性有重要作用。依据热点理论,当气泡或者气泡载体的尺寸在有效范围之内,且分布均匀时,则形成热点的时间接近,有利于爆炸反应的快速激发和传递,宏观上表现为乳化炸药爆轰感度、爆速和猛度等较大。     

Effect of quenching temperature on microstructure and performance of Al‐bearing cast boron steel

The effects of quenching temperature on microstructure and performance of Al‐bearing cast boron steel (ACBS) containing 0.25–0.45%C, 1.5–1.8%B and 1.4–1.6%Al were investigated by means of the optical microscopy (OM), the scanning electron microscopy (SEM), X‐ray diffraction (XRD), Rockwell hardness and Vickers micro‐hardness tester. The results show that the solidification structures of cast steel consist of high hardness boride, ferrite, pearlite and a small quantity of martensite when 1.5–1.8%B and 1.4–1.6%Al are added into the carbon steel. The metallic matrix of ACBS changes into single martensite from the mixed structure of ferrite, pearlite and martensite along with the increase of quenching temperature. The increase of quenching temperature also leads to the transformation of boride from continuous shape to isolated shape. Moreover, the micro‐hardness of matrix and macroscopical hardness increase with the increase of quenching temperature. When the quenching temperature excels 1000°C, the hardness has a slight decrease. ACBS has good comprehensive properties after heat treatment at 1000°C.     

Effect of cooling rate on microstructure,inclusions and mechanical properties of weld metal in simulated local dry underwater welding

Quenched and tempered E550 steel was joined using flux-cored arc welding. The effect of cooling rate on microstructure, inclusions and mechanical properties of the weld metal was investigated by optical microscope, scanning electron microscope, transmission electron microscope and mechanical testing. Results show that weld metal microstructures consist of proeutectoid ferrite, ferrite side plate and acicular ferrite. As the cooling rate increased, the volume fraction of proeutectoid ferrite and ferrite side plate decreased, acicular ferrite increased accompanied with refined grain. Furthermore, inclusions of Ti, Mn oxide with diameter below 2.0 μm were found in the weld metal and rapid cooling rate causes distinct Mn-depleted zone between inclusions and matrix. Excellent balance of high strength and toughness is obtained as more acicular ferrite in weld metal with rapid cooling rate. This can attribute to the increased of acicular ferrite with its refined grain and high density dislocation. These findings suggest that the rapid cooling rate can improve the impact toughness and tensile strength of weld metal in local dry underwater welding.