Experimental investigation on diamond wire sawing of Si3N4 ceramics considering the evolution of wire cutting performance

When diamond wire saw is used in machining silicon nitride ceramics (Si₃N₄ ceramics), the ultra-hardness of Si₃N₄ causes the saw wire to wear out, which leads to the saw wire cutting performance constantly changing during its life cycle, and thus the machined quality of Si₃N₄ ceramics is affected. Surface roughness and topography are important indicators of the quality of the machined surface. In this paper, the diamond wire saw cutting experiment of Si₃N₄ ceramics was carried out, the effect of the evolution of saw wire cutting performance on the surface roughness and topography of Si₃N₄ ceramics as-sawn slices was investigated based on the analysis of the changes of saw wire wear topography, breaking force, bow angle and kerf loss during the sawing process. The results show that the surface roughness along the saw wire motion direction and the workpiece feed direction tends to decrease and then increase with the evolution of the cutting performance of the saw wire, which accords well with the trend of the as-sawn slices surface morphology. The results of the study can provide experimental reference for the development of high precision diamond wire saw cutting technology for Si₃N₄ ceramics.     

The effect of traffic data source on deterioration rates of heavy-duty flexible pavements

The purpose of this study is to assess the effect of traffic data source (estimated vs. actual) on predicted progression rates of roughness and rutting for heavy-duty flexible pavements of rural freeways. Progression rates are predicted using calibrated HDM-4 models. The assessment is performed in terms of variations in maintenance intervention timing associated with the variations in progression rates. Time series pavement condition data (covering 3–5 years) have been collected for 7 sections of rural freeways for use in calibrating HDM-4 deterioration models. They range in length from 10 to 60.8 km and cover different traffic volumes, climate zones and subgrade soil types. For these sections, estimated annual average daily traffic (AADT), growth factors and assumed loading have been extracted from relevant database. Only six segments of these sections have Weigh-in-Motion (WIM) sites so relevant actual AADT, growth factors and axle load distributions have been extracted from WIM reports. The results of running the calibrated HDM-4 deterioration models using different traffic data show that actual traffic data from WIM sites result in higher rates of deterioration to that of estimated data for four sites, resulting in earlier intervention timing and higher present value agency cost. The other two sites have lower rates with actual data due to lower traffic loading than estimated.     

滚齿工艺对齿根粗糙度的影响

针对国内外风电和工业齿轮箱轻量化的设计趋势,较低的安全系数对齿轮齿根弯曲强度提出了更为严格的要求。研究表明,在材料技术和齿形设计难以再优化的情况下,滚齿加工的粗糙度,尤其是齿根部位的粗糙度对齿轮弯曲强度的影响尤为敏感。针对滚齿工艺过程,从滚齿加工参数、刀具前刀面粗糙度和刀具刃口圆角三方面进行分析,验证其对齿根粗糙度的影响。     

基于超声无损评价的表面粗糙度测量方法

选用不同线切割工艺制备各种表面粗糙度的304不锈钢试块。基于超声波入射到粗糙表面的自由应力边界条件，采用表面回波的幅值均值、离差率和平均功率同时表征粗糙度，根据主成分分析法建立粗糙度的多参数评价模型。实验结果表明，和触针法相比，超声评价法误差最大为3.09%，且其不确定度更低，将该模型用于含粗糙表面试块的晶粒尺寸评价中，评价误差小于5%，可见该方法能有效实现表面粗糙度及材料微观结构的一体化评价，可提高超声自动化评价系统的实用性。     

Investigations of geometrical structure and morphology of samples made of hard machinable materials after wire electrical discharge machining and vibro‐abrasive finishing

In this article the results concerned influence of processing conditions of the wire electrical discharge machining and vibro‐abrasive machining on the surface layer and morphology of samples made of hard machinable materials used in aircraft industry like: Titanium 5553 β, Inconel 617, Hastelloy X and Magnesium AZ31 have been presented. For this purpose the cubic and cylindrical samples made of hard machinable alloys have been prepared using optimal electric parameters of wire‐cut electrical discharge machining and finally they have been polished using circular vibratory finishing technology and different ceramic shaped stones.     

Heteroepitaxial growth of thick 3C-SiC (110) films by Laser CVD

Previously, we found 3C-SiC films favor to grow in <111> orientation on Si (110) ( https://doi.org/10.1111/jace.15260 ). However, epitaxial growth of thick <110>-3C-SiC is still a big challenge. In this study, thick 3C-SiC (110) epitaxial films were prepared on Si (110) substrate by laser chemical vapor deposition (LCVD) using hexamethyldisilane (HMDS) in H₂ atmosphere. The investigation of growth mechanism showed that the laser of LCVD played an important role during the depositions. Observation by high-resolution transmission electron microscopy (HRTEM) revealed that the interface of 3C-SiC (110)/Si (110) exhibited rough texture at atomic level. The atomic roughness on Si (110) surface could be a key factor for 3C-SiC (110) nucleation. The growth of thick 3C-SiC (110) epitaxial films could be very promising for new development in power electronics applications.     

Enhancing the Tribological Behavior of Lubricating Oil by Adding TiO2, Graphene,and TiO2/Graphene Nanoparticles

This article investigates the tribological behavior of nanoparticles (NPs) of titanium dioxide anatase TiO₂ (A), graphene, and TiO₂ (A) + graphene added to the pure base oil group ΙΙ (PBO-GΙΙ). The morphology of these two nanostructures of TiO₂ (A) and graphene was characterized by transmission electron microscopy (TEM). Oleic acid (OA) was blended as a surfactant into the formulation to help stabilize the NPs in the lubricant oil. A four-ball test rig was used to determine the tribological performance of six different samples, and an image acquisition system was used to examine and measure the wear scar diameter of the stationary balls. Field emission–scanning electron microscopy (FE-SEM) was used to examine the wear morphology. Energy-dispersive X-ray spectroscopy (EDX), element mapping, and Raman spectroscopy were employed to confirm the presence of (TiO₂ (A) + graphene) and the formation of a tribolayer/film on the mating surfaces. Moreover, a 3D optical surface texture analyzer was utilized to investigate the scar topography and tribological performance. The experiments proved that adding (0.4?wt% TiO₂ (A) + 0.2?wt% graphene) to the PBO-GΙΙ optimized its tribological behavior. These excellent results can be attributed to the dual additive effect and the formation of a tribofilm of NPs during sliding motion. Furthermore, the average reductions in the coefficient of friction (COF), wear scar diameter (WSD), and specific wear rate (SWR) were 38.83, 36.78, and 15.78%, respectively, for (0.4?wt% TiO₂ (A) + 0.2?wt% graphene) nanolubricant compared to plain PBO-GΙΙ lubricant.     

Effect of heat treatment on the roughness and mechanical properties of dental lithium disilicate glass-ceramics

In dental clinics, it is common to perform small fitting adjustments in dentures using a micro-grinding tool after testing them in the patient's mouth. This procedure increases local roughness and can lead to formation of microcracks on the prosthesis surface. This study aimed to investigate the benefits of a post-finishing heat treatment to surface roughness and crack healing and its effect on the flexural strength of lithium disilicate (LD) dental glass-ceramics. Commercially available lithium metasilicate, Li₂SiO₃, samples were heat treated at 840 °C for 7 min to induce the phase transformation into LD, Li₂Si₂O₅. The LD samples were characterized by X-ray Diffraction, Scanning Electron Microscopy, Vickers hardness, Young’s modulus, and fracture toughness. One of the surfaces of the LD samples was sanded aiming to simulate the denture fitting adjustments performed in the dentist’s laboratory, generating a rough surface, Group 1. Half of the LD samples had their biaxial flexural strength evaluated by the piston-on-three-ball test (P–3B) and the other half were submitted to a second short-term heat treatment (840 °C - 5 min), Group 2, and later assessed by the P–3B. Roughness parameters in both groups were measured by 3D optical profilometry. After the crystallization heat treatment, formation of elongated LD crystals, Li₂Si₂O₅, 35% amorphous phase, and residual Li₃PO₄ was observed. In addition, the following mechanical property values were obtained: Vickers hardness = 5.8 ± 0.1 GPa, fracture toughness = 2.2 ± 0.1 MPa m^1/2, and Young’s modulus = 100.3 ± 0.3 GPa. The samples in Group 1 showed bending strength of 206 ± 30 MPa and the following roughness parameters: Ra = 0.45 ± 0.16 μm, Rz = 22.7 ± 6.7 μm, and PV = 27.7 ± 7.1 μm. In the samples in Group 2, the Ra, Rz and PV roughness parameters were 0.31 ± 0.12 μm, 5.2 ± 2.5 μm, and 9.2 ± 4.7 μm, respectively. With this decrease in roughness, the bending strength increased by 62%, with a mean value of 331 ± 59 MPa. In the need for machine finishing of LD-based glass-ceramic dental prostheses, the use of a second short-term heat treatment at 840 °C for 5 min generates considerable gains in bending strength, increasing the lifecycle of the prosthesis as a result of reduced surface roughness caused by softening of the remaining amorphous phase in the glass-ceramic. These conditions can be adapted to each chemical and crystallographic composition of the glass-ceramic under study.     

Cathode plasma electrolytic deposition of Al2O3 coatings doped with SiC particles

Semiconductor particles doped Al₂O₃ coatings were prepared by cathode plasma electrolytic deposition in Al(NO₃)₃ electrolyte dispersed with SiC micro- and nano-particles (average particle sizes of 0.5–1.7?µm and 40?nm respectively). The effects of the concentrations and particle sizes of the SiC on the microstructures and tribological performances of the composite coatings were studied. In comparison with the case of dispersing with SiC microparticles, the dispersion of SiC nanoparticles in the coatings was more uniform. When the concentration of SiC nanoparticles was 5?g/L, the surface roughness of the composite coating was reduced by 63%, compared with that of the unmodified coating. Friction results demonstrated that the addition of 5?g/L SiC nanoparticles reduced the friction coefficient from 0.60 to 0.38 and decreased the wear volume under dry friction. The current density and bath voltage were measured to analyze the effects of SiC particles on the deposition process. The results showed that the SiC particles could alter the electrical behavior of the coatings during the deposition process, weaken the bombardment of the plasma, and improve the structures of the coatings.     

节理峰前剪切刚度软化模型及其影响因素分析

节理峰前剪切应力-位移曲线是研究节理剪切行为的重要内容。然而目前对于节理峰前剪切行为大多以线性描述,不能较好的描述非线性的特点。对于非线性的描述也仅仅是唯象描述剪切应力-位移曲线,未能反映影响模型的参数物理意义及影响因素。以峰前节理刚度软化行为为出发点,采用归一化的思想将节理剪切刚度与位移无量纲化,用双曲线函数表示出剪切刚度与位移之间的关系。提出了考虑刚度软化的峰前剪切本构关系,通过与试验结果对比验证了本构关系的合理性。影响该模型最重要的两个因素是初始剪切刚度与峰值剪切位移。以Greenwood和Williamson模型为基础在细观上探讨了初始剪切刚度的影响因素;抓住法向应力与节理粗糙度主要因素,探讨了影响峰值剪切位移的影响因素。对模型参数的研究有助于进一步阐明节理峰前剪切机理。