Embryo-damage induced nucleation of microcracks in an aluminum-alloy under impact loading

The nucleation of microdamage under dynamic loading was investigated through planar impact experiments accomplished with a light gas gun. The microscopic observation of recovered and sectioned specimens showed that microcracks were nucleated only by cracking of brittle particles inside material. However, for comparison the in situ static tensile tests on the same material conducted with a scanning electron microscope showed that the microcracks were nucleated by many forms those were fracture of ductile matrix, debonding particles from matrix and cracking of brittle particles. The quantitative metallographic observations of the specimens subjected to impact loading showed that most of the cracked particles were situated on grain boundaries of the aluminium matrix. These facts suggested the concept of critical size and incubation time of submicroscopic cavities in the dynamic case and the mechanism of embryo-damage induced nucleation by fracture of brittle particles in the aluminium alloy under impact loading was proposed.

Spall damage in aluminum-alloy

A void growth relations for ductile porous materials under intense dynamic general loading condition is presented. The mathematical model includes the influence of inertial effects, material rate sensitivity, as well as the contribution of void surface energy and material work-hardening. Numerical analysis shows that inertia appears to resist the growth of voids. The inertial effects increase quickly with the loading rates. The theoretical analysis suggests that the inertial effects cannot be neglected at high loading rates. Plate-impact tests of aluminum alloy are performed with light gas gun. The processes of dynamic damage in aluminum alloy are successfully simulated with a finite-difference dynamic code in which the theoretical model presented in this paper is incorporated.

Characteristics and microstructure in the evolution of shear localization in ti-6al-4v alloy

A new interrupting method was proposed and the split Hopkinson torsional bar (SHTB) was modified in order to eliminate the effect of loading reverberation on post-mortem observations. This makes the comparative study of macro- and microscopic observations on tested materials and relevant transient measurement of tau - gamma curve possible. The experimental results of the evolution of shear localization in in Ti-6Al-4V alloy studied with the modified SHTB are reported in the paper. The collapse of shear stress seems to be closely related to the appearance of a certain critical coalescence of microcracks. The voids may form within the localized shear zone at a quite early stage. Finally, void coalescence results in elongated cavities and their extension leads to fracture along the shear band.

Microstructures of explosively consolidated rapidly solidified aluminum and Al-Li alloy powders

The microstructures and the characteristics of water-atomized, nitrogen gas-atomized Al powders and ultrasonic argon gas-atomized Al-Li alloy powder were investigated by means of metallography, SEM, Auger electron spectroscopy and X-ray diffraction techniques. Rapidly solidified powders were explosively consolidated into different sized cylinders under various explosive parameters. The explosively consolidated compacts have been tested and analysed for density microhardness, retention of rapidly solidified microstructures, interparticle bonding, fractography and lattice distortion. It is shown that the explosive consolidation technique is an effective method for compacting rapidly solidified powders. The characteristics of surface layers play a very important role in determining the effectiveness of the joints sintered, and the Al-Li alloy explosive compacts present an abnormal softening appearance compared to the original powder.

Experimental-study on the criteria and mechanism of spallation in an aluminum-alloy

In this paper, a damage function defined by the residual strength of spalled specimens of an aluminium alloy is given to characterize the spallation of the material. Based on this function a simple method for continuously describing the spallation may be developed. Stress wave profiles showing the signal of spallation were successfully obtained with carbon gauges. Microscopic observations of the spalled aluminium alloy specimens reveal that the nucleation of spallation initiates from cracking of the second phase particles. Spallation is a process of crack nucleation, growth and coalescence to final, complete disintegration.

Alejandra Pizarnik: "Si no me escribo soy una ausencia"

[ES] Este trabajo propone una lectura de los seis primeros cuadernos del diario que Alejandra Pizarnik escribió a lo largo de toda su vida, desde los 18 años y hasta que murió a la edad de 36. El análisis de estos cuadernos, escritos entre 1954 y 1958, nos permite recorrer el itinerario que Alejandra Pizarnik realiza por la cuestión genérica, la cuestión nacional y la cuestión sexual. Desde su experiencia en cuanto sujeto, la escritura registra esta primera fase en la construcción del yo que Pizarnik desea para su diario. Esta fase, que se puede denominar etapa-derribo, está dominada por el desafío a las ideas del discurso hegemónico. Una vez haya resuelto este escollo en la construcción del yo de su diario, la escritura de Pizarnik no volverá sobre estos temas. Sin embargo, la búsqueda el “verdadero” yo se registra como proceso en el que a un movimiento de construcción del yo, le sigue un movimiento de destrucción de lo que las palabras han conformado, en secuencias en las que la apelación a la mentira de lo escrito o la desconfi anza en la capacidad del lenguaje para expresarlo, son la pauta de dicha escritura.

低能离子束方法制备磁性Fe-Si合金薄膜

　利用质量分离的低能离子束技术,获得了磁性Fe Si合金薄膜。利用俄歇电子能谱法(AES)、X射线衍射法(XRD)以及交变梯度样品磁强计(AGM)测试了样品的组分、结构以及磁特性。测试结果表明在室温下制备的Fe Si合金是Fe组分渐变的非晶薄膜,具有室温铁磁性。当衬底温度为300℃时制备的非晶Fe Si薄膜中有Fe硅化物FeSi相产生,样品的铁磁性被抑制。

铁磁/半导体异质结材料MnSb/Si的物理气相沉积生长

采用一种新的生长铁磁 /半导体异质结材料的方法——物理气相沉积方法生长了一种铁磁 /半导体异质结材料 Mn Sb/Si.对所获得的样品进行特征 X射线能谱分析表明 Mn和 Sb在 Si衬底上的沉积速率相近 ,它们的原子百分数之比接近 1∶ 1.X射线衍射分析发现薄膜中形成了 Mn Sb相 ,样品在室温下测出磁滞回线也从侧面验证了存在 Mn Sb相 .用原子力显微镜对样品的表面进行观察 ,发现 Mn Sb呈有规则形状的小晶粒状 ,晶粒大小比较均匀 ,尺寸大多数在 5 0 0 nm左右 .

低能离子束方法制备Fe组分渐变的Fe-Si薄膜

利用质量分离的低能离子束技术 ,获得了Fe组分渐变的Fe Si薄膜。利用俄歇电子能谱法 (AES)、X射线衍射法 (XRD)以及X射线光电子能谱法 (XPS)测试了薄膜的组分、结构特性。测试结果表明 ,在室温下制备的Fe Si薄膜呈非晶态。非晶薄膜在 40 0℃下退火 2 0min后晶化 ,没有Fe的硅化物相形成。退火后Fe Si薄膜的Fe组分从表面向内部逐渐降低。

喷射成形工艺参数及热挤压制度对8009耐热铝合金的组织及性能的影响

采用喷射成形方法制备了Al-8.5Fe-1.4V-1.7Si(8009)耐热铝合金，研究了喷射成形工艺参数及沉积坯件的热挤压工艺对材料的微观组织及性能的影响。结果表明：喷射成形工艺能够有效地抑制8009合金中粗大的富铁相的析出，获得均匀细小的组织；当射成形工艺参数选择适当时，沉积坯件具有良好的成形性与致密度，在随后的热挤压过程中，通过较低的挤压比即可使材料达到全致密。合金经过热挤压后，在室温及高温下均具有良好的力学性能。

低能离子束方法制备重掺杂Fe的Si∶Fe固溶体

利用质量分离的低能离子束方法 ,以离子能量为 1 0 0 0 e V,剂量为 3× 1 0 1 7cm- 2 ,室温下往 p型 Si(1 1 1 )单晶衬底注入 Fe离子 ,注入的样品在 4 0 0℃真空下进行热处理 .俄歇电子能谱法 (AES)对原位注入样品深度分析表明 Fe离子浅注入到 p型 Si单晶衬底 ,注入深度约为 4 2 nm.X射线衍射法 (XRD)对热处理样品结构分析发现只有 Si衬底的衍射峰 ,没有其他新相 .X射线光电子能谱法 (XPS)对热处理样品表面分析发现 Fe2 p束缚能对应于单质 Fe的峰 ,没有形成 Fe的硅化物 .这些结果表明重掺杂 Fe的 Si∶ Fe固溶体被制备 .电化学 C- V法测量了热处理后样品载流子浓度随深度的分布 ,发现 Fe重掺杂 Si致使 Si的导电类型从 p型转为 n型 ,Si∶ Fe固溶体和 Si衬底形成 pn结 ,具有整流特性