Acoustic emission of composite materials in tensile tests at cryogenic temperatures

Tensile tests of fibre reinforced plastics are performed at cryogenic temperatures and simultaneously acoustic emission (AE) is observed to examine the microscopic deformation and fracture processes of these materials. AE behaviours at liquid helium temperature are different from those at liquid nitrogen temperature, although the mechanical behaviours are similar. From these results, correlations of the AE sources with the microscopic deformation and fracture processes are discussed.     

Effect of deep cryogenic treatment on mechanical properties and microstructure of Sn3.0Ag0.5Cu solder

The effect of deep cryogenic treatment on the performance of steels and alloys has attracted wide attention in the past decades. Deep cryogenic treatment can improve the strength and hardness of steel at room temperature, provide microstructure stability and improve wear or fatigue resistance of material. In the current study, the effect of deep cryogenic treatment on the microstructure and mechanical properties of Sn3.0Ag0.5Cu solders are investigated. The influence to microstructure, tensile strength and ductility improvement are discussed. Experimental analysis shows that the tensile strength of Sn3.0Ag0.5Cu solder increases from 36.76 to 46.27 MPa after 600 h of deep cryogenic treatment at 77 K (??196 °C), the observed strength-time relation is similar to the Taylor theory for the yield strength and dislocation density. Large particles presented in the fracture of Sn3.0Ag0.5Cu samples are caused by the high cooling rate as well as the concentration difference between the β-Sn and the eutectic system. The precipitated Ag₃Sn particles exhibit relatively uniform distribution in deep cryogenic treated Sn-rich matrix, and the size of Ag₃Sn particles becomes smaller with longer deep cryogenic treatment time. It is noted that deep cryogenic treatment can increase the internal stress and the dislocation density, higher dislocation density and good ductility lead to movement of the pre-existing dislocations and specific dislocation configurations. Microscopic experiments on solder joints were performed to investigate the microstructure change. The Intermetallic layers were measured which showed negligible change in thickness. A unified creep and plasticity constitutive model is proposed to simulate the stress–strain relationship under deep cryogenic treatment, the predictions show good agreement compared with experimental results.     

Annealing effect to constitutive behavior of Sn–3.0Ag–0.5Cu solder

Sn–Ag–Cu based solder alloys are replacing Sn–Pb solders in electronic packaging structures of commercial electric devices. In order to evaluate the structural reliability, the mechanical property of solder material is critical to the numerical simulations. Annealing process has been found to stabilize material properties of Sn–37Pb solder material. In the current study, the annealing effect on tensile behaviour of Sn–3.0Ag–0.5Cu (SAC305) solder material is investigated and compared with Sn–37Pb solder. It is found that the tensile strength for both materials are more stabilized and consistent after the annealing process, nevertheless, the annealing process will improve the plasticity of SAC305 solder dominated by dislocation motion, and impede the occurrence of hardening deformation in Sn–37Pb solder dominated by grain-boundary sliding mechanism. Furthermore, the annealing effect is quantified in the proposed constitutive model based on unified creep–plasticity theory. The parameters are calibrated against the measured stress–strain relationships at the tensile strain rates ranging from 1?×?10^?4 to 1?×?10^?3 s^?1. The numerical regressions for dominant parameters in the proposed model reveal the intrinsic differences between SAC305 and Sn–37Pb solders under annealing treatment.     

Investigation of microstructures and tensile properties of a Sn-Cu lead-free solder alloy

In recent years, the pollution of environment from lead (Pb) and Pb-containing compounds in microelectronic devices attracts more and more attentions in academia and industry, the lead-free solder alloys begin to replace the lead-based solders in packaging process of some devices and components. In this work, microstructures and mechanical properties of the lead-free solder alloy Sn99.3Cu0.7(Ni) are investigated. This paper will compare the mechanical properties of the lead-based with lead-free solder alloys (Sn99.3Cu0.7(Ni) and 63Sn37Pb). The tensile tests of lead-based and lead-free solder alloys (Sn99.3Cu0.7(Ni) and Sn63Pb37) were conducted at room and elevated temperature at constant strain rate; the relevant tensile properties of Sn99.3Cu0.7(Ni) and Sn63Pb37 were obtained. Specifically, the tensile strength of this lead-free solder- Sn99.3Cu0.7(Ni) in 25^∘C, 50^∘C, 75^∘C, 100^∘C, 125^∘C was investigated; and it was found that tensile strength of the lead-free solder decreased with the increasing test temperature at constant strain rate, showing strong temperature dependence. The lead-free solder alloy Sn99.3Cu0.7(Ni) was found to have favorable mechanical properties and it may be able to replace the lead-based solder alloy such as Sn63Pb37 in the packaging processes in microelectronic industry.     

Copper effects in mechanical,thermal and electrical properties of rapidly solidified eutectic Sn–Ag alloy

The Sn–3.5 wt%Ag alloy considered as a good alternative to Pb–Sn alloys. This study aims to investigate the effects of Cu or Sb additions by 3 or 5 wt% to melt-spun Sn–3.5%Ag alloy. Ternary melt-spun Sn–Ag–Cu and Sn–Ag–Sb alloys investigated using X-ray diffractions (XRD), Scanning electron microscope (SEM), Dynamic resonance technique (DRT), Instron machine, Vickers hardness tester and Differential scanning calorimetry (DSC). The results revealed that the microstructures of the β-Sn phase, Ag₃Sn and Cu₃Sn intermetallic compounds (IMCs) in the solder matrices were refined due to the effect of Cu additions and melt-spun process. Moreover, increasing Cu content promotes Ag₃Sn intermetallic compound (IMC) formation. Consequently, the addition of “3 wt%” of Cu reduced the creep rate ? from (3.79?×?10^?3) to (1.65?×?10^?3) and delayed the fracture point. The tensile results showed an improvement in Young’s modulus by 47% (30.3 GPa), ultimate tensile strength (UST) by 11.6% (23.9 MPa), and in toughness by 20.5% (952.32 J/m³) compared to the eutectic Sn–Ag alloy. Vickers hardness has improved by 3.3% (136.71 MPa) and thermal activation energy by 54% (90.40 KJ/mol) when compared with that of eutectic Sn–Ag alloy. Those improvements are related to the lack of lattice strain from 7.56?×?10^?4 without “3 wt%” of Cu to 5.26?×?10^?4 with “3 wt%” of Cu. Its melting temperature (T_m) increased by 3 °C due to Ag₃Sn IMC increased and Cu₃Sn formation, but the pasty rang (mushy zone) decreased by 4 °C with “3 wt%” of Cu. The small lattice strains resulted with “3 wt%” of Cu made the electrical resistivity of this alloy more stable at elevated temperatures. The mechanical, thermal and electrical improvements of Sn_93.5–Ag_3.5–Cu₃ alloy provide good physical performance for soldering process and electronic assembly.     

Tensile properties and wettability of SAC0307 and SAC105 low Ag lead-free solder alloys

In this article, the tensile properties of low Ag lead-free solder alloys, SAC0307 and SAC105, are examined under various strain rates and temperatures. The wettability of these solders on Cu pad is also characterized by using different fluxes. The SAC305 and Sn37Pb solder alloys are also studied for comparison. Our results show that the properties of all solder alloys are dependent on the strain rate and temperature. The ultimate tensile strength increases monotonously with the increment of strain rate. Both SAC0307 and SAC105 alloys possess lower strength and higher elongation ratio than SAC305 and Sn37Pb alloys. For all the fluxes used in this study, the SAC0307 and SAC105 alloys show the similar wettability to SAC305, whereas worse than that of Sn37Pb alloy. Increasing the activity of the flux does not improve the wettability of the SAC solder alloys on Cu pad effectively.     

Nanoparticles of Sn3.0Ag0.5Cu alloy synthesized at room temperature with large melting temperature depression

The Sn3.0Ag0.5Cu (wt%) lead-free solder alloy is considered to be one of the most promising alternatives to replace the traditionally used Sn–Pb solders. This alloy composition possesses, however, some weaknesses, mainly as a result of its higher melting temperature compared to the eutectic Sn–Pb solders. Nanoparticles of Sn3.0Ag0.5Cu lead-free solder alloy nanoparticles were prepared by chemical reduction with NaBH₄ as a reducing agent at room temperature. The melting temperature of the synthesized Sn3.0Ag0.5Cu alloy nanoparticles was determined by differential scanning calorimetry (DSC). The results showed that the calorimetric onset melting temperature of the Sn3.0Ag0.5Cu alloy nanoparticles could be as low as 200 °C, which was about 17 °C lower than that of the bulk alloy (217 °C). The field emission scanning electron microscopy (SEM) images of the as-prepared nanoparticles indicated that the major particle size of Sn3.0Ag0.5Cu nanoparticles is smaller than 50 nm. The structure and morphology of the nanoparticles were analyzed with high resolution transmission electron microscopy (HRTEM). The Ag3Sn and Sn phase were observed in the HRTEM images, which was in good agreement with the XRD results. These low melting temperature Sn3.0Ag0.5Cu alloy nanoparticles show a potential to manufacture high quality lead-free solders for electronic products.     

镀锡银钎料扩散过渡区的物相和形成机制

采用温度梯度法对镀锡银钎料进行热扩散处理,形成了扩散过渡区。为了揭示镀锡银钎料扩散过渡区的形成机制和主要物相的形成过程,借助金相显微镜、扫描电镜(SEM)、能谱分析仪(EDS)、X射线衍射分析仪(XRD)对扩散过渡区的显微组织、Sn元素的面扫描分布、物相组成及形貌进行分析。研究表明,Sn元素在镀锡银钎料中分布均匀、无偏析,在扩散过渡区主要以棒状Ag_3Sn相和块状Cu_3Sn相存在。随着热扩散温度升高,Ag_3Sn相和Cu_3Sn相的相对衍射强度逐渐增大。Ag_3Sn相的形成过程分为三个阶段:Ag_3Sn颗粒相弥散分布、Ag_3Sn颗粒相互相接触合并、生成大块棒状化合物相。Cu_3Sn相主要是锡晶须生长冲破镀层的氧化膜,在张应力和压应力协同作用下形成。镀锡银钎料扩散过渡区的形成机制为"钎接、互扩散、亚稳态、合金化"。     

SiO2/环氧树脂基纳米复合材料的室温和低温力学性能

利用溶胶-凝胶法制备了SiO₂/环氧树脂基复合材料,研究了材料的室温与低温(77 K)下的力学性能。结果表明,适量SiO₂的引入提高了室温与低温下材料的拉伸强度、断裂伸长率和冲击强度,即SiO₂含量在2%时可同时起到增强、增韧作用。采用扫描电镜(SEM)和透射电镜 (TEM)分别对复合材料的断口形貌和高温焚烧后残留物纳米颗粒进行了观察。还利用动态力学分析(DMA)研究了二氧化硅的引入对复合材料的影响。      

Melting and solidification properties of the nanoparticles of Sn3.0Ag0.5Cu lead-free solder alloy

The Sn3.0Ag0.5Cu (wt.%) lead-free solder alloy is considered to be one of the most promising candidates to replace the traditionally used Sn–Pb solder. However, this alloy composition has some weaknesses, mainly as a result of its higher melting temperature compared to the eutectic Sn–Pb solder. In this paper, lead-free solder alloy nanoparticles of Sn3.0Ag0.5Cu were synthesized by chemical reduction with NaBH₄ as reducing agent. The experimental results indicated that the major particle size of Sn3.0Ag0.5Cu nanoparticles was smaller than 100 nm. The melting and solidification properties of the Sn3.0Ag0.5Cu nanoparticles were studied by differential scanning calorimetry at different scanning rates. It was evidenced by the differential scanning calorimetry curves that the melting temperature of Sn3.0Ag0.5Cu nanoparticles was lower than that of the bulk alloy. In addition, the undercooling of the Sn3.0Ag0.5Cu nanoparticles was in the range of 82.0–88.5 °C at different cooling rates, which was much larger than that of the Sn3.0Ag0.5Cu micro-sized particles, showing stronger cooling rate dependence.     

Sn对电真空Ag-Cu钎料组织和性能的影响

利用扫描电镜及其能谱仪、同步热分析仪以及对比实验来分析Sn对电真空Ag-Cu钎料微观组织、熔化特性和钎焊性能的影响。结果表明:Sn添加4%(质量分数,下同)时,Ag60Cu钎料中没有脆性β-Cu相生成,对钎料的加工性能影响不大;随着Sn含量的增加,Ag60Cu钎料的液相线温度逐渐降低,同时固相线温度降低幅度更大,导致熔化温度范围扩大,钎料的填缝性能变差;对于含Sn为4%的Ag60Cu钎料,与紫铜的铺展性能以及冶金结合性能都接近于BAg72Cu钎料,并可通过压力加工制成片状钎料,可以用来替代BAg72Cu片状钎料使用。     

Analysis of mixed-mode interlaminar fracture and damage behavior of GFRP woven laminates at cryogenic temperatures

The objective of this work is to investigate the interlaminar fracture and damage behavior of glass fiber reinforced polymer (GFRP) woven laminates loaded in a mixed-mode bending (MMB) apparatus at cryogenic temperatures. The finite element analysis (FEA) is used to determine the mixed-mode interlaminar fracture toughness of MMB specimen at room temperature (RT), liquid nitrogen temperature (77 K) and liquid helium temperature (4 K). A FEA coupled with damage is also employed to study the damage distributions within the MMB specimen and to examine the effect of damage on the mixed-mode energy release rate. The technique presented can be efficiently used for characterization of mixed-mode interlaminar fracture and damage behavior of woven laminate specimens at cryogenic temperatures.     

Thermal properties of Sn-based solder alloys

During last few decades, emerging environmental regulations worldwide, more notably in Europe and Japan, have targeted the elimination of Pb usage in electronic assemblies due to the inherent toxicity of this element. This situation drives to the replacement of the Sn–Pb solder alloy of eutectic composition commonly used as joining material to suitable lead-free solders for microelectronic assembly. Sn-based alloys containing Ag, Cu, Bi, and Zn are potential lead-free solders, usually close to the binary or ternary eutectic composition. For this reason a great effort was directed to establish reliable thermophysical data fundamental to interpret the solidification process and fluidity of alloys belonging to these systems. In this work, an analysis of the solidification process of pure Sn, binary Sn–Ag, Sn–Cu, Sn–Bi, Sn–Zn, Sn–Pb and ternary Sn–Ag–Cu eutectic alloys was carried out using computer aided-cooling curve analysis and differential scanning calorimetry.     

Mixed-mode interlaminar fracture and damage characterization in woven fabric-reinforced glass/epoxy composite laminates at cryogenic temperatures using the finite element and improved test methods

The present research examines experimentally and analytically the mixed-mode interlaminar fracture and damage behavior of glass fiber reinforced polymer (GFRP) woven laminates at cryogenic temperatures. The mixed-mode bending (MMB) tests were performed with the improved test apparatus, at room temperature, liquid nitrogen temperature (77 K) and liquid helium temperature (4 K). The energy release rates at the onset of delamination crack propagation were evaluated for the woven GFRP specimens using both beam theory and finite element analysis. The fracture surfaces were also examined to verify the fracture mechanisms. In addition, the initiation and growth of damage in the specimens were predicted by a damage analysis, and the damage effect on the mixed-mode interlaminar fracture properties at cryogenic temperatures was explored.     

Cryogenic Interlaminar Fracture Properties of Woven Glass/Epoxy Composite Laminates Under Mixed-Mode I/III Loading Conditions

We characterize the combined Mode I and Mode III delamination fracture behavior of woven glass fiber reinforced polymer (GFRP) composite laminates at cryogenic temperatures. The eight-point bending plate (8PBP) tests were conducted at room temperature, liquid nitrogen temperature (77 K) and liquid helium temperature (4 K) using a new test fixture. A three-dimensional finite element analysis was also performed to calculate the energy release rate distribution along the delamination front, and the delamination fracture toughnesses were evaluated for various mixed-mode I/III ratios. Furthermore, the microscopic examinations of the fracture surfaces were carried out with scanning electron microscopy (SEM), and the mixed-mode I/III delamination fracture mechanisms in the woven GFRP laminates at cryogenic temperatures were assessed. The fracture properties were then correlated with the observed characteristics.     

Mode III fatigue delamination growth of glass fiber reinforced polymer woven laminates at cryogenic temperatures

This paper investigates the cryogenic fatigue delamination behavior of glass fiber reinforced polymer woven laminates under Mode III loading. Fatigue delamination tests were conducted using split cantilever beam specimens at room temperature, liquid nitrogen temperature (77 K) and liquid helium temperature (4 K). A finite element analysis was also employed to calculate the energy release rate. The temperature dependence of the fatigue delamination growth rate vs. energy release rate range is discussed. Fracture surfaces were examined by scanning electron microscopy to identify the delamination mechanisms under fatigue loading. The important conclusion we reach is that the Mode III fatigue delamination growth rates of woven laminates at cryogenic temperatures are lower than that at room temperature.     

Passive ZBO storage of liquid hydrogen and liquid oxygen applied to space science mission concepts

Liquid hydrogen and oxygen cryogenic propulsion and storage were recently considered for application to Titan Explorer and Comet Nuclear Sample Return space science mission investigations. These missions would require up to 11 years of cryogenic storage. We modeled and designed cryogenic propellant storage concepts for these missions. By isolating the propellant tank’s view to deep space, we were able to achieve zero boil-off for both liquid hydrogen and oxygen propellant storage without cryocoolers. Several shades were incorporated to protect the tanks from the sun and spacecraft bus, and to protect the hydrogen tank from the warmer oxygen tank. This had a dramatic effect on the surface temperatures of the propellant tank insulation. These passive storage concepts for deep space missions substantially improved this application of cryogenic propulsion. It is projected that for missions requiring larger propellant tank sizes, the results would be even more dramatic.     

Cryogenic delamination growth in woven glass/epoxy composite laminates under mixed-mode I/II fatigue loading

This paper investigates the fatigue delamination growth behavior in woven glass fiber reinforced polymer (GFRP) composite laminates under mixed-mode I/II conditions at cryogenic temperatures. Fatigue delamination tests were performed with the mixed-mode bending (MMB) test apparatus at room temperature, liquid nitrogen temperature (77 K) and liquid helium temperature (4 K), in order to obtain the delamination growth rate as a function of the range of the energy release rate, and the dependence of the delamination growth behavior on the temperature and the mixed-mode ratio of mode I and mode II was examined. The energy release rate was evaluated using three-dimensional finite element analysis. The fractographic examinations by scanning electron microscopy (SEM) were also carried out to assess the mixed-mode fatigue delamination growth mechanisms in the woven GFRP laminates at cryogenic temperatures.     

Mechanisches Verhalten von kohlenstoffaserverstärkten Duromeren im Tieftemperaturbereich

Investigations on the suitability of carbon fiber reinforced epoxy for using at cryogenic temperatures The following investigations show the mechanical properties of some carbon fiber reinforced epoxies under quasistatic load. Both prepregs and wet laminates are tested to get a suitable fiber/matrix-combination for using at cryogenic temperatures. Therefore the material research is done at room temperatures. Therefore the material research is done at room temperature and at liquid nitrogen atmosphere. The characteristics, which serve for the basis of valuation are ultimate strength, elongation at fracture and modulus of elasticity. At liquid nitrogen temperature ultimate tensile strength and elongation at fracture show a decrease in comparison to room temperature, but Young's Modulus increases insignificantly with tensile loading. In the compression test all the characteristics grow larger. Furthermore the influence of the testing temperature on the mechanical characteristics of prepregs and wet laminates is pronounced differently. The experiments also show, that the dependence of the temperature on the mechanical properties may be influenced by the kind of the reinforcing fibers. This statement applies especially to the value of the obtainable interlaminar shear strength.     

Sn2.5Ag0.7CuxRE钎料时效焊点界面IMC研究

以Sn2.5Ag0.7CuxRE/Cu钎焊为研究对象,借助于扫描电镜和X衍射检测手段,研究了二硫化钼介质下时效焊点界面IMC组织结构特征及生长行为。实验结果表明:时效焊点界面Cu6Sn5IMC呈现由波浪状→扇贝状→层状的形态变化。焊点界面Cu6Sn5和Cu3Sn IMC的生长厚度与时效时间平方根呈线性关系,Cu6Sn5IMC具有较小的生长激活能、较大的生长系数。添加0.1%(质量分数)RE时,界面Cu6Sn5和Cu3Sn IMC的生长激活能最大,分别为81.74 kJ/mol和92.25 kJ/mol,对应焊点剪切强度最高。