Al—Fe系梯度功能材料断口特征及其多尺度分形研究

研究了Ａｌ－Ｆｅ系梯度功能材料的试样不同部位的断口特征；基于离散分形布朗随机场模型，对试样断口进行多尺度分形研究，结果表明断口的分形参数Ｈ值也呈梯度分布，它反映了该材料的韧性呈梯度分布。     

内部氢对奥氏体不锈钢拉伸断口分形维数的影响

采用热充氢方法研究了1Cr18Ni9Ti、21Cr6Ni9Mn、Fe31Cr14Ni奥氏体不锈钢的氢脆性能。采用垂直截面法测量了不同热充氢时间拉伸试样的断口分形维数,分析了材料氢脆性能与分形维数的相关性。研究表明:随着充氢时间的延长,3种材料内部氢含量增加、断面收缩率降低、氢致塑性损减增加。反映在断口分形维数上,表现为断口分形维数随充氢时间的延长而降低,且断口分形维数与其断面收缩率呈线性相关。断口分形维数能够描述氢对材料性能的影响。     

D6AC钢冲击断口形貌的分形研究

本文利用扫描电镜对含Mn$夹杂物和含ZrN夹杂物的D6AC钢的冲击断口形貌进行了观察与分析;利用数字图象法测定了试样的断口分形维数,揭示了冲击断口形貌和冲击韧性与夹杂物含量之间的内在联系,探讨了材料冲击断口形貌与分形维数的关系,拓宽了分形几何学在材料领域的应用范围.     

分形维数与D6AC钢的韧性

本文研究了超高强度钢Ｄ６ＡＣ的断裂韧性、冲击韧性和拉伸面缩率与断口分形维数的关系。分别用二次电子线扫描和数字图像法断裂韧性试样的断口分形维数，得出试样的韧性与分形维数Ｄｓｅ，ＤＨ和ＤＬ成正比关系，即韧性随分形维数增大而增加。试样断口的粗糙度由夹杂物引起差异小于金相组织不同引起的差异时，使用数字图象法测得的分形维数与韧性的线性关系优于二次电子线扫描的结果。     

D6AC钢冲击断口形貌的分形研究

本文利用扫描电镜对含MnS夹杂物和含ZrN夹杂物的D6AC钢的冲击断口形貌进行了观察与分析;利用数字图象法测定了试样的断口分形维数,揭示了冲击断口形貌和冲击韧性与夹杂物含量之间的内在联系,探讨了材料冲击断口形貌与分形维数的关系,拓宽了分形几何学在材料领域的应用范围。     

分形维数与D6AC钢的韧性

本文研究了超高强度钢Ｄ６Ａｃ的断裂韧性、冲击韧性和拉伸面缩率与断口分形维数的关系。分别用二次电子线扫描和数字图象法测定断裂韧性试样的断口分形维数，得出试样的韧性与分形维数Ｄｓｅ、Ｄ_Ｈ和Ｄ_Ｌ成正比关系，即韧性随分形维数增大而增加。试样断口的粗糙度由夹杂物引起的差异小于金相组织不同引起的差异时，使用数字图象法测得的分形维数与韧性的线性关系优于二次电子线扫描的结果。     

分形几何在金属材料力学性能研究中的应用

叙述了分形几何在金属材料力学性能研究中的应用。重点介绍了金属材料力学性能试验试样断口的分形分析,并指出了力学性能研究近期动向的热点。     

Ni/ZrO2梯度镀层的制备和性能

采用Watt型镀镍溶液，恒电流电沉积方法制备Ni／ZrO2梯度镀层．扫描电镜(SEM)测试和X-射线衍射分析表明，沿镀层的生长方向，ZrO2的含量由0逐渐增加到21％(体积分数，下同)，呈梯度分布；Ni和ZrO2各自在特定的角度分别出现其衍射特征峰，互不干扰，镀层中ZrO2的含量增高，衍射强度变强．断口分析表明，在梯度镀层的内部，材料的塑性变形能力大，韧性最好；沿镀层生长的方向，断口中的韧窝特征逐渐减小，镀层的韧性下降；在表层的断口中ZrO2微粒明显增多，呈团聚状态，基本上没有韧窝特征，镀层的韧性最差．Ni／ZrO2梯度镀层的韧性由外至内逐渐增加，呈梯度分布，其延展性为复合镀层的2．5倍．     

粉末NBR-PVC共混型热塑性弹性体断裂面的分形维数

本文利用扫描电镜对粉末NBR-PVC共混型热塑性弹性体拉伸断面形貌进行了观察与分析;基于断面小岛周长-面积关系,测定了试样的断口分形维数,考察了NBR含量、拉伸断面分形维数、力学性能(拉伸强度、断裂伸长率、邵氏硬度)之间的关系。结果表明,NBR-PVC弹性体拉伸断面的分形维数随着NBR含量的增加而增加,当NBR含量超过29份后其分形维数呈下降趋势;分形维数与材料的拉伸强度、断裂伸长率和邵氏硬度变化关系一致。     

材料断口分形维数分析

本文分析了应用分形维数描述材料断口轮廓形貌几何特征的局限性。结果指出，分形维数对于材料断口粗糙度的变化是不敏感的，该参数与材料断口轮廓几何形态和断裂韧性之间不存在确定性的关系。     

A Fractal Study on Brittle-Ductile Transition forTi-24Al-11Nb Alloy

The mechanical behaviours of Ti-24Al-11Nb alloy in the brittle-ductile transition (BOT) have been investigated by using three-point bending tests. The temperature dependence of the fractal dimensions and fractal characterization of fracture surfaces are presented. The probable mechanism controlling BDT of intermetallic alloys are proposed according to fractal geometry.Additionally. it is found that there is a positive relationship between the fractal dimension and fracture toughness in BDT for Ti-24Al-11Nb alloy     

Characterization of grain-boundary configuration and fracture surface roughness by fractal geometry and creep-rupture properties of metallic materials

Grain-boundary configuration in heat-treated specimens and fracture surface roughness in creep-ruptured specimens of several kinds of metallic material were quantitatively evaluated on the basis of fractal geometry. Correlations between the fractal dimension of grain boundary, that of fracture surface profile, the creep-rupture properties and the fracture mechanisms of the alloys are discussed. In heat-resistant alloys, the fractal dimension of a nominally serrated grain boundary was always larger than that of a straight grain boundary in the same alloy. The relative importance of the ruggedness of grain boundaries was estimated by the fractal dimension difference between these two grain boundaries. There was a quantitative relationship between the increase of the fractal dimension of the grain boundary and the improvement of rupture ductility and rupture strength owing to grain-boundary serration in the alloy. A similar correlation was also found between the increase in the fractal dimension of the fracture surface profile and the improvement of the creep-rupture properties, since in some cases the fractal dimension of the fracture surface profile was correlated with that of the grain boundary. Both grain boundary and fracture surface profile were assumed to exhibit a fractal nature between one grain boundary length (upper bound) and an interatomic spacing (lower bound). In carbon steels with ferrite-pearlite structure, according to the increase in pearlite volume fraction, the rupture ductility decreased and the fracture mechanism changed from transgranular fracture in pure iron and low-carbon steels to intergranular fracture at ferrite-pearlite grain boundaries in medium-carbon steels, and further to intergranular fracture at pearlite grain boundaries in high-carbon steels. The correspondence between the fractal dimension of the grain boundary and that of the fracture surface was confirmed in ruptured specimens of ferrite-pearlite steels when the grain boundary was the fracture path.     

垂直截面法测量的断口分形维数与7475 Al 合金超塑性的关系

本文利用垂直截面法测量了7475Al 合金在不同温度、不同应变速率及不同晶粒尺寸条件下超塑拉伸变形时断裂表面的分形维数。结果表明:断裂表面的分形维数越高,合金超塑拉伸破断时的延伸率越大。     

The fourth mode of fracture in fractal fracture mechanics

This paper offers a systematic approach for obtaining the order of stress singularity for different self-similar and self-affine fractal cracks. Mode II and Mode III fractal cracks are studied and are shown to introduce the same order of stress singularity as Mode I fractal cracks do. In addition to these three classical modes, a Mode IV is discovered, which is a consequence of the fractal fracture. It is shown that, for this mode, stress has a weaker singularity than it does in the classical modes of fracture when self-affine fractal cracks are considered, and stress has the same order of singularity when self-similar cracks are considered. Considering this new mode of fracture, some single-mode problems of classical fracture mechanics could be mixed-mode problems in fractal fracture mechanics. By imposing a continuous transition from fractal to classical stress and displacement fields, the complete forms of the stress and displacement fields around the tip of a fractal crack are found. Then a universal relationship between fractal and classical stress intensity factors is derived. It is demonstrated that for a Mode IV fractal crack, only one of the stress components is singular; the other stress components are identically zero. Finally, stress singularity for three-dimensional bodies with self-affine fractal cracks is studied. As in the two-dimensional case, the fourth mode of fracture introduces a weaker stress singularity for self-affine fractal cracks than classical modes of fracture do.     

多相材料断裂的分形特征

测量了多相材料复合涂层的断裂挠度和断口表面的分形维数，分析了复合涂层的断裂特征。结果表明：随着硬质相增加，复合涂层的断裂挠度和断口表面的分形维数降低。     

SiCw/Al-Al3Ni复合材料断口的分维特征

本文所研究的复合材料,其基体Al-Al₃Ni合金具有很好的组织热稳定性,因而可以通过改变拉伸温度并在组织结构基本不发生变化的情况下,使材料的分维和断裂功发生变化.分维的测量采用断口轮廓法(FPM).研究结果指出,SiCw/Al-Al₃Ni复合材料的分维可分为三部分,每部分分维存在的尺寸范围与组织结构有一定的对应关系.文中还讨论了断裂功与分维之间的关系.     

Fractal aspects of ductile and cleavage fracture surfaces

The aim of this paper is to evaluate and interpret the three-dimensional variational fractal dimension of a ductile and a cleavage fracture surface. The fracture surface is acquired by fracturing Charpy impact and static loaded specimens of a low alloy steel in ductile-to-brittle transition temperature range, and reconstructed by a stereoscopic technique. The three-dimensional variational method for measuring fractal dimension is improved by shifting algorithm and tested on the Takagi surface using the local fractal dimension. We find very good fractal behaviour in the ductile area, however, fractal characteristics in the cleavage area are less noticeable. The results are discussed in thermodynamical terms and promote the idea that fractal behaviour reflects the quasi-static process and that the fracture mechanisms in the ductile fracture are independent of strain rate (at least up to 10³ s⁻¹).     

Fractal in Fatigue Fractography

Fracture profile roughnesses and fractal dimensionsof fracture traces were measured on a fatigued Ti-6Al-4Valloy.It is found that although fractal dimension can wellreflect the variation of fracture traces with the measuringunits,it is difficult to apply it to quantitative analysis offractured surfaces because of the dependence of the meas-ured profile roughness on the measuring units.Based onfractal concept.an alternative equationlgR_l(η)=lgR_o-(D-1)lgη was obtained.in which we intro-duced a parameter of intrinsic profile roughness to evalu-ate fracture profile roughness without restriction of themeasuring units employed.     

不同应变率下MgAlZnY合金的拉伸性能与断口研究

利用材料试验机开展了室温拉伸实验,在0.001,0.1,0.6s-1不同应变率下,研究了Mg3Al1Zn2Y,Mg3Al2Zn2Y与Mg3Al6Zn2Y合金流动应力的应变率敏感性,其大小为Mg3Al2Zn2YMg3Al1Zn2YMg3Al6Zn2Y。基于分形理论和计算机图像处理技术,结合扫描电镜分析,研究了合金断裂特征,结果表明:合金在不同应变率拉伸下的断口分形行为显著,分形维数可将断口的韧脆性与形貌特征联系起来,分形维数越大,合金塑性相对越好,合金越倾向于延性断裂,断口形貌也越复杂;三种合金断裂特性的应变率敏感性大小为Mg3Al2Zn2YMg3Al6Zn2YMg3Al1Zn2Y,且表现出正负不同的应变率效应。     

铁钴钒软磁合金损耗谱的分形结构

研究了铁钴钒软磁合金的铁芯损耗，发现铁芯损耗谱具有分形结构。讨论了带材厚度和磁感应强度对分形维数Ｄｆ的影响。