Hard transparent dielectric coatings

Hard transparent corrosion-resistant dielectric coatings were investigated (a) for application to the direct protection of glass surfaces, (b) for application to the protection of thin film metallic window coatings used for reflection or transmission of solar radiation and (c) for use in codeposited metal-ceramic coatings. The dielectric coatings were Al₂O₃, SiO₂ and SiC in the thickness range 100–100 000 Å. The coatings were deposited under varying conditions of substrate temperature, gas composition, r.f. power and substrate preparation. The results of the following measurements on the dielectric coatings are presented: diamond pyramid hardness tests, optical reflectance and transmittance in the region 0.6–4.0 eV and corrosion resistance tests under cyclic conditions. The results showed a considerable improvement in the scratch resistance and hardness of glass by layering of hard dielectric coatings 2–5 μm thick.     

Hard plasmachemical a-SiCN coatings

The amorphous SiCN coatings have been plasmachemically (PECVD) deposited onto silicon substrates using the heksamethyldisylazan as the basic precursor. The effect of the deposition temperature on the structure, chemical composition, and mechanical properties of the coatings has been studied. It has been found that at temperatures below 400°C the deposition of hydrogenated amorphous SiCN (a-SiCN:H) coatings, whose hardness does not exceed 23 GPa, takes place. At the further increase of the temperature the distribution of the Si–C, Si–N, and C–N strong bonds in coatings does not practically change, while the number of C–H, Si–H and N–H weak hydrogen bonds decreases. As a result of such a redistribution of chemical bonds, at the temperature 600–700°C a-SiCN coatings are deposited with hardness up to 32 GPa. The annealing in vacuum at 1200°C is shown not to noticeably affect the structure, hardness, and elastic modulus of a-SiCN coatings.     

地质聚合物混凝土的冲击力学性能研究

摘 要：以矿渣与粉煤灰为原材料,制备地质聚合物混凝土（geopolymeric concrete, GC）。采用Φ100 mm分离式霍普金森压杆（split Hopkinson pressure bar, SHPB）装置研究了不同强度等级的GC的冲击力学性能,包括抗压强度、变形及能量吸收特性的应变率效应问题。结果表明：GC的冲击力学性能呈现出显著的应变率相关性,强度的应变率敏感值为42.7 s-1;随着强度等级的提高,GC的变形能力反而降低。GC属于准脆性材料,相对于单一的强度或变形特性,GC的能量吸收特性更值得关注。     

Three dimensional fracture analysis of FGM coatings under thermomechanical loading

The main objective of this study is to examine the three dimensional surface crack problems in functionally graded coatings subjected to mode I mechanical or transient thermal loading. The surface cracks are assumed to have a semi-elliptical crack front profile of arbitrary aspect ratio. The cracks are embedded in the functionally graded material (FGM) coating which is perfectly bonded to a homogeneous substrate. A three dimensional finite element method is used to solve the thermal and structural problems. Collapsed 20-node isoparametric elements are utilized to simulate the strain singularity around the crack front. The stress intensity factors are computed by using the displacement correlation technique. Four different coating types are considered in the analyses which have homogeneous, ceramic-rich (CR), metal-rich (MR) and linear variation (LN) material composition profiles. In the mechanical loading problems, the composite medium is assumed to be subjected to fixed-grip tension or three point bending. In the thermal analysis, a transient residual stress problem is considered. The stress intensity factors calculated for FGM plates are in good agreement with the previously published results on three dimensional surface cracks. The new results provided show that maximum stress intensity factors computed during transient thermal loading period for the FGM coatings are lower than those of the homogeneous ceramic ones.     

单轴动态加载下冻土的力学性能实验研究

为研究冻土单轴加载下的冲击动态力学性质,采用分离式霍普金森压杆(SHPB)在-28～-3℃不同负温下对人工冻土进行了应变率范围800～1500s-1的冲击实验.获得了人工冻土在不同温度与不同应变率下的应力应变关系,发现人工冻土具有显著的应变率效应和温度效应,即冻土动强度随应变率增大和温度的降低而增大.单轴高应变率加载下,冻土没有明显的屈服现象,加载后试样完全破坏.     

动载下胶结充填体的力学特性试验研究

胶结充填体的稳定性对于矿山安全生产至关重要。为了研究动载作用下充填体的动力学特性,利用霍普金森压杆(SHPB)对充填体进行单轴冲击试验,研究充填体应力应变曲线、动态抗压强度、动态强度增长因子与平均应变率之间的关系。结果表明,当平均应变率低于60 s^(-1)时,应力应变曲线峰后阶段为"应变回弹"类型;超过80 s(-1)时,应力应变曲线峰后阶段为"应变回弹"类型;超过80 s^(-1)时,为"峰后塑性"类型;介于二者之间时,为"应力跌落"类型;随着平均应变率的增大,试样动态抗压强度先迅速增大,后趋于稳定,对应的平均应变率临界值为80 s(-1)时,为"峰后塑性"类型;介于二者之间时,为"应力跌落"类型;随着平均应变率的增大,试样动态抗压强度先迅速增大,后趋于稳定,对应的平均应变率临界值为80 s^(-1)。利用Gompertz模型能较好的描述充填体动态抗压强度与平均应变率之间的关系;动态强度增长因子与平均应变率正相关,当平均应变率处于40～130 s(-1)。利用Gompertz模型能较好的描述充填体动态抗压强度与平均应变率之间的关系;动态强度增长因子与平均应变率正相关,当平均应变率处于40～130 s^(-1),动态强度增长因子范围在1.5～3之间。     

Dynamic deflection of perimeter-attached thin-sheet structural components under blast loading

The results of experimental investigations of the relation the pressure pulse of blast products and the deflection of thin-sheet structural components with a circular and rectangular attachment perimeter under a loading are presented. The relationship between the relative deflection and specific (per unit mass of the loaded portion of the plate) kinetic energy imparted to the plate being deformed is determined.Translated from Problemy Prochnosti, No. 4, pp. 94–96, April, 1993.     

Residual strength evaluation of concrete structural components under fatigue loading

This paper presents methodologies for residual strength evaluation of concrete structural components using linear elastic and nonlinear fracture mechanics principles. The effect of cohesive forces due to aggregate bridging has been represented mathematically by employing tension softening models. Various tension softening models such as linear, bilinear, trilinear, exponential and power curve have been described with appropriate expressions. These models have been validated by predicting the remaining life of concrete structural components and comparing with the corresponding experimental values available in the literature. It is observed that the predicted remaining life by using power model and modified bi-linear model is in good agreement with the corresponding experimental values. Residual strength has also been predicted using these tension softening models and observed that the predicted residual strength is in good agreement with the corresponding analytical values in the literature. In general, it is observed that the variation of predicted residual moment with the chosen tension softening model follows the similar trend as in the case of remaining life. Linear model predicts large residual moments followed by trilinear, bilinear and power models.     

主动围压下岩石的冲击力学性能试验研究

利用具有主动围压加载装置的直径为100 mm分离式Hopkinson压杆（SHPB）试验装置和薄圆形紫铜片作为波形整形器,研究了斜长角闪岩在不同围压等级（0~6 MPa）、不同应变速率（50~170 s-1）下的动态力学性能,并对试验有效性进行了分析。试验结果表明：斜长角闪岩的动态强度增长因子与应变率的对数呈近似线性关系,强度与比能量吸收随应变率的增加而近似线性增加,体现了显著的应变率相关性;在同等级应变率范围内,随着围压的增加,岩石的增强效果与增韧效果逐渐增强;同时发现,在围压作用下,岩石的破坏由拉伸破坏向压剪破坏逐渐过渡和发展。SHPB试验中,近似恒应变率加载时间比例约为69.5 %,能够较好地满足应力均匀分布及近似恒应变率加载要求,表明SHPB试验的有效性和结果的可靠性     

Hard implant coatings with antimicrobial properties

Infection of orthopaedic implants often leads to inflammation immediately after surgery and increases patient morbidity due to repetitive operations. Silver ions have been shown to combine good biocompatibility with a low risk of inducing bacterial resistance. In this study a physical vapour deposition system using both arc deposition and magnetron sputtering has been utilized to produce silver ion doped TiN coatings on Ti substrates. This biphasic system combines the advantages of silver induced bactericidity with the good mechanical properties of TiN. Crystallographic analysis by X-ray diffraction showed that silver was deposited as well in its elementary form as it was incorporated into the crystal lattice of TiN, which resulted in increasing hardness of the TiN-coatings. Elution experiments revealed a continuous release of Ag ions in phosphate buffered saline. The coatings showed significant inhibitory effects on the growth of Staphylococcus epidermidis and Staphylococcus aureus and practically no cell-toxicity in cytocompatibility tests.     

Reliability assessment of polysilicon MEMS structures under mechanical fatigue loading

This paper examines the current status and methodologies of study of material and system reliability in Microelectromechanical Systems (MEMS). This includes: a review of the current literature in the area of MEMS regarding failure analysis experimental investigations; testing methods and philosophies for material characterization and possible mechanistic analytical solutions for estimating material properties. The paper proposes a reliability framework that encompasses all the available information. This statistical platform will enable the MEMS design engineer to distill all the available information in the literature into a stand-alone semi-empirical material reliability model, and a holistic system-level model for a complete system.     

Transversely isotropic mechanical properties of PVC foam under cyclic loading

Cyclic material tests were done on Divinycell PVC H100 foam to obtain out-of-plane and in-plane compression and shear material properties after foam yielding. The compression and shear stress–strain behaviors were very similar to each other except that a plateau (flow) stress occurred after yielding in compression, while the foam underwent mild strain hardening after shear yielding. The ratio of out-of-plane to in-plane stiffness and yield strength for the PVC H100 was found to be approximately 3/2 in both the compression and shear modes. After viscoplastic yielding, the foam underwent permanent damage and exhibited hysteresis, mainly in the form of viscoelasticity. Damage that occurred in the foam after it yields followed the pattern of Mullins damage, i.e., the damage was essentially fixed at a given strain amplitude, and more damage occurred with increasing the strain amplitude. Hysteresis was much more pronounced as the damage grew, suggesting that viscoelastic properties of the foam could be changing with the amount of damage.     

Endurance of alloy ZhS6U with protective coatings under thermocyclic loading

Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Problemy Prochnosti, No. 8, pp. 42–47, August, 1989.     

冲击荷载作用下EPS混凝土动态性能研究

配置聚苯乙烯(Expanded Polystyrene,EPS)颗粒体积掺量分别为10%,20%,30%,40%,50%的EPS混凝土,采用Φ100 mm分离式霍普金森压杆(SHPB)试验装置,以动态抗压强度和临界应变为指标,研究EPS混凝土在冲击荷载作用下的动态性能,探索EPS颗粒对混凝土动态性能的改善机理。结果表明:由于应变率效应,相同体积掺量的EPS混凝土动态抗压强度与临界应变随应变率的增加而提高,具有显著的应变率相关性;以临界应变为变形性能指标,由于EPS颗粒的微结构效应,在EPS颗粒体积掺量0～40%范围内,其变形性能随EPS体积掺量的增加而提高,当EPS颗粒体积掺量达到50%时,其变形能力有所降低。EPS颗粒体积掺量为40%时对混凝土变形性能的改善效果最佳。     

Study of surface damage of polypropylene under progressive loading

A systematic study of surface damage exerted by a progressive scratching load is performed on model polypropylene (PP) systems. Mar-scratch and stress-whitening transitions can be readily observed, and the corresponding critical loads determined. Distinctive surface damage features are determined before and after the transitions. The progressive load test enables the scratch hardness values to be obtained using the graphical method, thereby allowing scratch resistance to be accurately quantified and ranked among materials. Visibility of the scratched surface is quantified using a gray level analysis via a flatbed scanner and a commercial image analysis tool. It is found that the onset of scratch visibility can be determined accurately and reproducibly using the custom-built scratcher under progressive loading condition. Exposed talc particles on the surface of talc-filled PP are found to be responsible for the increased light scattering, leading to greatly increased visibility. The observed scratch visibility is also found to be related to the corresponding friction force profiles. Approaches for producing scratch resistant PP are discussed.     

Microstructure based fatigue analysis of cast components under variable amplitude loading

Reliable numerical fatigue life analyses are becoming increasingly important given the need to reduce the time and costs for product development and the need to evaluate large and single components. Stress‐based approaches as well as the local strain approach and its fracture mechanics based extension (P_J model) are in use for that. Both the local strain approach and the P_J model require the supply of pure material data. This requirement for input data that are not component‐specific makes such approaches interesting for widespread application. The accuracy of numerical fatigue life analyses is an essential criterion for the acceptance and the spread in industrial application. In the local strain approach, accuracy is determined on one hand by the transferability of material data for the fatigue life analysis of components and on the other by the damage accumulation rule. In this paper, the local strain approach and the P_J model are used to analyse fatigue life under both constant and variable amplitude loading. These analyses are based on the experimental results obtained from tests of a commercial vehicle component made of nodular cast iron EN‐GJS‐400‐15. Aspects of transferability and damage accumulation are considered. Results obtained from using an elastic‐plastic fracture mechanics based approach to estimate a P_SWT‐N curve, taken into account the inhomogeneities in the microstructure of the cast iron, are also presented.