Characteristics of thermo-acoustic emission from composite laminates during thermal load cycles

The thermo-acoustic emission (AE) technique has been applied for nondestructive characterization of composite laminates subjected to cryogenic cooling. Thermo-AE events during heating and cooling cycles showed a Kaiser effect. An analysis of the thermo-AE behavior obtained during the 1st heating period suggested a method for determining the stress-free temperature of the composite laminates. Three different thermo-AE types classified by a short-time Fourier transform of AE signals enabled to offer a nondestructive estimation of the cryogenic damages of the composites, in that the different thermo-AE types corresponded to secondary microfracturing in the matrix contacting between crack surfaces and some abrasive contact between broken fiber ends during thermal load cycles.     

Piercing in delicate materials with abrasive-waterjets

Abrasive waterjets (AWJs) have proven to be a versatile tool for precision machining of a variety of materials and are applicable to virtually any material; there is no heat-affected zone, no tooling, fast turnaround, and is cost-effective for large and small lot sizes. Nevertheless, damage to delicate material may occur during the initial piercing stage. The large buildup of piercing pressure (p _p) inside blind holes is responsible for the damage. Laboratory results show that p _p decreases with the hole depth. At 345 MPa, waterjet-induced p _p in an AWJ-pierced blind hole was measured and extrapolated to be about 180 MPa at the target surface. Such a large p _p exceeds the ultimate strength of many delicate materials such as laminates, composites, glass, and other brittle materials. We have discovered that the phase change of the working fluid of liquefied nitrogen (LN₂) in an abrasive cryogenic jet (ACJ) is an effective means to mitigate piercing damage. Most of the LN₂ evaporates before entering the blind hole, significantly reducing the piercing pressure. This paper investigates the causes and extent of piercing damage induced by AWJs. Understanding such causes has led to the development of a cost-effective flash abrasive waterjet (FAWJ) to emulate the phase change of the ACJ for mitigating piercing damage. The mechanisms leading to the mitigation of piercing damage by the FAWJ are described qualitatively and quantitatively. Comparison of the visual results of holes pierced in several delicate materials with AWJs and FAWJs is presented to correlate the extent and the mitigation of damage with the piercing pressure.     

等离子喷涂层和钢的制动磨损特性

在ＭＭ—１０００制动摩擦磨损试验机上,试验了两种不同组成的Ｆｅ－Ｎｉ－Ｃｏ－ＷＣ复合涂层并与传统的钢制件作比较。试验结果表明,涂层比钢的耐磨性有较大的提高,ＷＣ质量分数高的涂层耐磨性更好。制动时涂层的磨损以磨粒磨损为主,有轻微的氧化和粘着。钢的氧化磨损和粘着比涂层严重。因摩擦热的影响,制动后钢的摩擦表面出现热震开裂和特有的浅层剥落,浅层剥落是一个塑性变形积累、裂纹形成和扩展的过程。但涂层无热震开裂和浅层剥落现象。     

热障涂层层状裂纹的位置对断裂性能的影响

广泛应用于热能动力的热障涂层在高温工作环境下,由于温度梯度产生的热应力不匹配会导致热障涂层层裂或剥落失效。本文针对热障涂层层裂问题,考虑热应力不匹配因素,建立热障涂层层裂I/II复合型断裂准则,并针对分层裂纹在陶瓷层与粘结层界面上和附近的3种位置存在形式,进行了热障涂层结构单裂纹层裂的算例分析。结果表明界面处层裂纹对应变能释放率影响最大。     

微磨料浆体射流的浆体配制及钻孔性能研究

微磨料浆体射流技术是在微磨料水射流加工技术基础上发展起来的一种新技术。通过添加分散剂和悬浮剂来提高浆体的沉降稳定性;为了配制出优质钻孔浆体,研究了磨料质量浓度、磨料种类、分散剂体积分数和悬浮剂体积分数对钻孔加工的影响,并研究了分散剂体积分数和悬浮剂体积分数对浆体沉降稳定性的影响。研究结果表明：磨料质量浓度存在最佳取值;分散剂并非一定能改善颗粒的沉降稳定性,这与磨料种类、磨料质量浓度和分散剂体积分数等有关;悬浮剂能够改善浆体的悬浮性,其体积分数影响浆体的沉降稳定性和钻孔效果。     

A New Shaft Sealing Solution for Small Cryogenic Pumps

Commonly scaled cryogenic fluids include liquefied gases such as nitrogen, argon and oxygen, pumped both on site and from road tankers at temperatures approaching — 200°C (392°F). Traditionally, cryogenic sealing has employed conventional contact sealing technology, the seal typically being of a metal bellows design.

However, because most liquefied gases are pumped at temperatures close to their boiling points, vaporization at the sealing interface is a major problem. Dry running causes accelerated face and seat wear and short seal life.

A new type of seal has been developed which combines two critical seal, technologies. It comprises a profiled noncontacting seal face and seal as the primary seal, and a welded metal bellows as the secondary seal, and spring.

The paper will outline the technology employed in solving this cryogenic sealing application. It will describe the equipment and environments that are typically employed, focusing on those issues that are relevant, to the shaft seal. Some examples of operating installation will be given, together with measurements taken from them.     

Ultimate strength of composite laminates with free-edge delamination

The present paper deals with the free edge effect of composite laminates by using a generalized quasi-three dimensional analysis and experimental verification of an analysis performed for laminates with Teflon inserted on interfaces to simulate initial free-edge delamination. We performed tensile tests for laminates [30₂/?30₂/90]_s carbon-epoxy laminates with free-edge delamination under uniaxial tension. The experiment reveals that extensional stiffness of the laminate decreases by the initiation of the delamination, and that strength of the laminate without delamination is smaller than that of the laminates with delamination. Generalized quasi-three dimensional finite element technique, which employs energy release rate and maximum stress criteria, is developed to estimate behavior of the laminate after initial delamination. The numerical result by use of this technique predicts the ultimate strength of the laminates with sufficient accuracy according as the comparison with an experimental stress-strain curve. In the experiment conducted both for the laminate with initial delamination and the laminate without initial delamination, an unexpected results were obtained that is the ultimate load of the laminate without initial delamination was lower than that of the laminate with initial delamination. We presented clear explanation on the phenomenon occurred and developed the method to predict the nonlinear behavior of the laminate with or without initial delamination.     

Fine-particle slurry wear resistance of selected tungsten carbide thermal spray coatings

The surface degradation of tungsten carbide based thermal spray coatings when exposed to fine-particle slurry abrasion has been investigated. The coatings that were studied contain binder-phase constituents consisting of either nickel or cobalt. The coatings were deposited onto test cylinders using a detonation gun device. After applying approximately 0.15 mm thickness of thermal spray coating, the coatings were ground, then diamond polished to achieve surface roughnesses of 0.03 μm Ra or less. The coatings were exposed to a three-body abrasive wear test involving zirconia particles (less than 3 μm diameter) in a water-based slurry. Results show that preferential binder wear plays a significant role in the wear of these tungsten carbide coatings by fine abrasives. In the comparison presented here, the coating containing nickel-based binder with a dense packing of primary carbides was superior in terms of retaining its surface finish upon exposure to abrasion. The coating containing a cobalt binder showed severe surface degradation.     

WC-10Co-MoS2@Ni自润滑硬质合金与钛合金的摩擦学性能研究

为探究WC-10Co-MoS2@Ni自润滑硬质合金与TC4钛合金的摩擦学性能，通过热压烧结制备不同含量MoS2@Ni的硬质合金试样，采用扫描电子显微镜、三维轮廓仪、维氏硬度计等分析自润滑硬质合金的组织结构和力学性能，利用往复式摩擦试验机研究干摩擦、切削液环境和深冷环境下硬质合金与钛合金的摩擦学性能。结果表明：随着硬质合金中MoS2@Ni含量的增加，表面孔隙减少，力学性能缓慢下降；在干摩擦、切削液环境和深冷环境下，摩擦因数均随MoS2@Ni含量的增加而降低；钛合金和硬质合金在干摩擦时由于钛合金的黏附，阻碍了MoS2发挥润滑作用，磨损形式以黏着和氧化为主；在切削液环境中磨损形式以磨粒磨损和黏着磨损为主，而在深冷环境下减少了氧化和黏着，其磨损形式主要为磨粒磨损，并伴有分层磨损现象。     

Lubrication effect of liquid nitrogen in cryogenic machining friction on the tool-chip interface

The liquid nitrogen as an environmentally safe coolant has been widely recognized in cryogenic machining, its function as a lubricant is plausible due to its chemical inertness, physical volatility and low viscosity. Since a reduced friction is a direct witness of the lubrication effect from a tribological viewpoint, this paper presents an evaluation of the apparent friction coefficient on the tool-chip interface in cryogenic cutting operations to prove and characterize the lubricity of LN2 in cryogenic machining. The cryogenic cutting technology used in this study is based on a cooling approach and liquid nitrogen delivery system which are intended to apply liquid nitrogen in well-controlled fine jets to selectively localized cutting zones and to penetrate liquid nitrogen to the tool-chip interface. It has been found that the apparent friction coefficient can be significantly reduced in cryogenic machining, depending on the approach of liquid nitrogen delivery.     

Fabrication of stepped hole on zirconia bioceramics by ultrasonic machining

Zirconia (ZrO₂) is a highly biocompatible ceramic material providing fracture strength properties that allow application as dental implants in biomedical engineering. In this present research, experimental analysis has been made for generating stepped hole on zirconia bioceramics with desired quality using ultrasonic machining (USM) process. Four independent controllable input process parameters are abrasive grain diameter, power rating, concentration of abrasive slurry, and tool feed rate. Material removal rate (MRR), overcut of larger diameter (OLD) hole, and overcut of smaller diameter (OSD) hole of stepped hole are considered as the responses. Response surface methodology (RSM) is used for modeling the performance of USM process. Multiobjective optimization has been performed to maximize the MRR and minimize the OLD hole and OSD hole of stepped holes. All the responses are improved at the optimal parametric condition and verified by confirmation test. The present research opens up the application feasibility of USM process for stepped hole generation on bioceramics and its utilization in biomedical field.     

Analysis on profile accuracy for ultrasonic machining of alumina ceramics

Ultrasonic machining (USM) is a mechanical material removal process which has great potential for machining hard and brittle materials such as ceramics, semiconductors, glasses, etc. The accuracy of the job profile generated by USM can be improved by optimal control of the process parameters. This paper presents the study on the influences of ultrasonic machining process parameters such as abrasive grit size, slurry concentration, power rating, tool feed rate and slurry flow rate on generated hexagonal hole profile. The angular deviations at corner angles, dimensional deviations across flat surfaces and dimensional deviation across corners of the hexagonal hole profile have been studied. Based on experimental results, the influences of abrasive grit size, slurry concentration, power rating and tool feed rate were analysed. From the analysis of parametric influences based on various test results, the best parametric combination was found as grit number of 600, slurry concentration of 30 %, power rating of 50 % and feed rate of 1.08 mm/min for achieving better profile accuracy during machining of Al₂O₃ ceramics. The experimental investigations carried out for determining the influence of USM process parameters will provide effective guideline to select parametric settings for achieving desired job profile accuracy on non-circular holes during ultrasonic drilling of alumina.     

多丝切割加工中研磨液的运动分析

多丝切割加工机理的研究多以单磨粒的“滚-刻”和硬脆材料的崩裂切除为推论,以“滚-刻”、“滚-刻-削”混合加工模型描述实际的多丝切割加工过程。文章认为切割加工的关键在于研磨粒,而研磨粒的综合力学行为在相当程度上取决于硅碇和金属丝之间研磨液的流体力学行为。基于加工区域研磨液的的运动分析,研磨液的速度分布支持磨粒滚动的假设,研磨液流体的动压力（剪切力）的分布支持磨粒磨削切割的存在。文章的结论支持“滚-刻”、“滚-刻-削”混合模型的切割加工机理。     

Study of tribological properties of coating/substrate system in micrometer and nanometer scales with a scanning probe microscope

We have used a scanning probe microscope equipped with a custom made diamond tip to study tribological properties of an inorganic–organic hybrid Si, O, H, and C coating produced by plasma enhanced chemical vapor deposition (PECVD) on siloxane/acrylic/polycarbonate multilayer substrates and on glass substrates. The micro indentation hardness and micro mar resistance were measured under different normal forces, and the critical loads for cracking, delamination, and chipping were evaluated. The effects of substrate, coating thickness, and interfacial adhesion on tribological properties of the coating/substrate systems are discussed. The results show that increasing coating thickness and strengthening interfacial adhesion can effectively inhibit cracking, delamination, and chipping of the coating/substrate systems under wear. Improving the physical properties of the PECVD coating and substrate, such as enhancing elastic recovery, reducing plasticity and brittleness, and matching the properties of coating and substrate better can improve the wear resistance of the systems further.     

复合材料含损伤结构剩余强度分析

考虑层压结构受冲击后的“花生壳形”分层及分层损伤引起的局部不对称性和耦合效应,并考虑压缩加载过程中可能出现的多层分级屈曲,发展一种计算低能冲击层压板受压剩余强度计算方法。数值分析表明本文的预测结果与试验结果吻合良好。     

Cryogenic gas loading in a Mao-Bell-type diamond anvil cell for high pressure-high temperature investigations

A simple system for loading argon fluid at cryogenic temperatures in a Mao-Bell-type diamond anvil cell (DAC) has been developed. It is done in a two step process in which the piston-cylinder assembly alone is submerged in the cryogenic chamber for trapping the liquefied inert gas. Liquid nitrogen is used for condensing the argon gas. This system is now being efficiently used for loading liquid argon in the DAC for high pressure-high temperature experiments. The success rate of trapping liquefied argon in the sample chamber is about 75%. The performance of the gas loading system is successfully tested by carrying out direct conversion of pyrolitic graphite to diamond under high pressure-high temperature using laser heated DAC facility.     

Comparative Study of Thermally Sprayed Coatings Under Different Types of Wear Conditions for Hard Chromium Replacement

The tribological properties of part surfaces, namely their wear resistance and friction properties, are decisive in many cases for their proper function. To improve surface properties, it is possible to create hard, wear-resistant coatings by thermal spray technologies. With these versatile coating preparation technologies, part lifetime, reliability, and safety can be improved. In this study, the tribological properties of the HVOF-sprayed coatings WC–17%Co, WC–10%Co4%Cr, WC–15% NiMoCrFeCo, Cr₃C₂–25%NiCr, (Ti,Mo)(C,N)–37%NiCo, NiCrSiB, and AISI 316L and the plasma-sprayed Cr₂O₃ coating were compared with the properties of electrolytic hard chrome and surface-hardened steel. Four different wear behavior tests were performed; the abrasive wear performance of the coatings was assessed using a dry sand/rubber wheel test according to ASTM G-65 and a wet slurry abrasion test according to ASTM G-75, the sliding wear behavior was evaluated by pin-on-disk testing according to ASTM G-99, and the erosion wear resistance was measured for three impact angles. In all tests, the HVOF-sprayed hardmetal coatings exhibited superior properties and can be recommended as a replacement for traditional surface treatments. Due to its tendency to exhibit brittle cracking, the plasma-sprayed ceramic coating Cr₂O₃ can only be recommended for purely abrasive wear conditions. The tested HVOF-sprayed metallic coatings, NiCrSiB and AISI 316L, did not have sufficient wear resistance compared with that of traditional surface treatment and should not be used under more demanding conditions. Based on the obtained data, the application possibilities and limitations of the reported coatings were determined.     

基于应变损伤模型的复合材料层合板低速冲击数值模拟

提出了一种基于应变的复合材料损伤模型,考虑了复合材料冲击过程中出现的面内纤维断裂与压缩,基体开裂与挤裂。在使用Abaqus软件进行数值模拟计算时,自编的用户子程序VUMAT和Cohe-sive模型分别实现了复合材料面板的损伤和层间分层。通过对层合板在不同能量下的低速冲击的有限元模拟发现,模拟得到的分层损伤形状和面积、冲头最大挠度、接触力和凹坑深度都与试验结果吻合较好。     

Coriolis mass flow measurement at cryogenic temperatures

With the growing interest in liquefied natural gas (LNG) in the energy market, Coriolis mass flowmeters have been applied to many applications in the distribution of LNG. Since Coriolis flowmeters are normally calibrated at around room temperatures, measurements for LNG at cryogenic temperatures present a challenging condition. Firstly, a theoretical analysis for Coriolis mass flow sensors is provided considering the major changes of material properties (Young’s modulus and thermal expansion) at cryogenic temperatures. Then, a practical approach which can be used to correct the flow calibration factor obtained at a reference condition is presented. Finally, flow test results obtained from NIST’s cryogenic calibration facility are provided. Based on the results, it can be concluded that if a Coriolis flowmeter is calibrated at a reference condition and the flow calibration factor is corrected considering the non-linearity of Young’s modulus and thermal expansion change with temperature, it can still provide very accurate mass flow measurement even at cryogenic temperatures.     

Effect of temperature on the magnetic abrasive finishing process of Mg alloy bars

Experiments were conducted to evaluate the effect of temperature during magnetic abrasive finishing of Mg alloy bars. A magnetic abrasive finishing process is an unconventional finishing technique that has been used to achieve high-quality surfaces with dimensional accuracy. In this study, a Mg alloy bar, which is widely used in automobiles, aircraft, IT, and the defense industry, was chosen as a cylindrical workpiece. The workpiece was then finished with a magnetic abrasive finishing process at three different temperatures, i.e., a cryogenic temperature, room temperature, and high temperature. In the cryogenic temperature condition, liquid nitrogen and argon gas were used as the cryogenic cooling gases in the finishing process; the results from this treatment were compared with those obtained at room temperature and high temperature conditions. At the room temperature condition, the finishing process of the cylindrical workpiece was performed at 24 °C. To carry out the high temperature condition, a hot air dryer was used to maintain a finishing temperature of 112 °C. The experimental results show that the room and cryogenic temperatures could yield excellent performance in terms of the surface roughness. However, in terms of the removal weight and change in diameter, the high temperature condition was found to be superior. In the present research, the improvements of the surface roughness (Ra) at room temperature (24 °C) and cryogenic temperature (-120 °C) conditions were 84.21 % and 55 %, respectively.