Effect of chamfer width and chamfer angle on tool wear in slot milling

The tool geometry is generally of great significance in metal cutting performance. The response surface method was used to optimize chamfer geometry to achieve reliable and minimum tool wear in slot milling. Models were developed for edge chipping, rake wear, and flank wear. The adequacy of the models was verified using analysis of variance at a 95% confidence level. Each response was optimized individually, and the multiple responses were optimized simultaneously using the desirability function approach. The Monte Carlo simulation method was applied to tolerance analysis. All milling tests were conducted at dry conditions; the chamfer width and the chamfer angle varied between 0.1 and 0.3 mm, and 10 and 30°, respectively. Optimal chamfer geometry for minimizing chipping and rake wear was small chamfer width and chamfer angle. The flank wear reached the minimum value for the tool with 0.18 mm chamfer width and 10° chamfer angle. The obtained composite model predicted good edge strength and minimum overall wear when the chamfer was 0.1 mm wide at a 10° angle. Thermal cracks were observed on the tools. They were small on the edges with the finest and least negative chamfer but were more significant on the more negative and greater chamfer. A great chamfer width and chamfer angle also resulted in insufficient chip evacuation. The results show how the edge geometry affects the tool’s reliability and wear and may help manufacturers minimize tool cost and downtime.

Identification of Fracturing Behavior In Thermally Cracked Granite Using The Frequency Characteristics of Acoustic Emission

The frequency characteristics of acoustic emission (AE) during triaxial compression of thermally cracked and unheated (“fresh”) granite samples were investigated with the aim of understanding the influence of pre-existing cracks on precursor information regarding macroscopic failure. The peak frequency during the damage process was the same for thermally cracked and fresh granites. Analysis of AE signals showed that signals with low peak frequency appeared before failure of the sample, implying the initiation of microfractures with progressive growth of cracks. The peak amplitude of the frequency spectrum recorded in the thermally cracked samples was much lower than that in the fresh samples. This result suggests two reasons for the difference in peak amplitude: reduction in shear modulus and the attenuation filtering phenomenon caused by thermal cracks. In particular, the maximum value of peak amplitude in the low-frequency band for the thermally cracked samples was smaller than that for fresh samples. This characteristic can be related to the stress drop and crack size. Assuming that pre-existing thermal cracks grow during the pre-failure stage, the events with low peak frequency and low peak amplitude in the heat-treated samples are interpreted as exhibiting a low stress drop because of the small rupturing area for individual events. Therefore, although AE signals with low frequency can be considered as precursors to rock failure, cracking behavior suggested by events with low frequency depends on the initial damage condition of the rock sample.

Full-scale dynamometer tests of composite railway brake shoes: Effect of the resin-rubber ratio on friction performance and wear

Designing a friction material for a brake system entails considering the effects of each constituent and the interactions that they may present between them. In the present work, a characterization of the influence of the resin-rubber ratio in a brake block material is carried out. Railway brake shoes were produced and tested in a full-scale railway dynamometer in demanding conditions. The brake blocks had also their physical and mechanical properties tested. The progressive addition of resin was proven to heavily affect the friction level in dry and wet conditions. Interestingly, the use of 5% of resin showed significantly higher friction in wet conditions. This composition also presented more severe metal pick-up. The nature of the binder also affected wear rates (which were lower for lower resin contents), and the wear mechanism. The sample using only rubber presented thermal cracks and heavier delamination as specific failure modes. Differences on the microstructure of the friction materials were observed depending on the binder. A 5% of resin appears as a very interesting choice to avoid friction loss in wet environments without incurring in high wear rates, as long as metal pick-up is by different means diminished. Otherwise, a 100% of rubber as a binder grants the instantaneous friction stability that is often threaten by thermal fade.

Estimation of Internal Maximum Thermal Stress of Tunnel Side Wall Lining Concrete During Construction Period

Thermal cracks in lining concrete of large section hydraulic tunnel usually occur in side walls during construction, and most of them are harmful penetrating cracks. In order to meet the needs of real-time rapid control for engineering design in construction period, nine influencing factors of maximum tensile of side wall lining concrete σmax during construction period are determined on the basis of comprehensive analysis of temperature stress effects and finite element simulations, and their influencing regularities are analyzed. Then the estimation formula of σmax and real-time control method of thermal crack are put forward. Through the application of real-time temperature control and crack prevention control of lining concrete in flood discharge tunnel, the estimation formula of σmax and the real-time thermal crack control method are proved to be correct and applicable.

Thermal Cracks Development Study in Newly Built Reinforced Concrete Residences

Concrete blocks and concrete assemblies are affected by natural physical conditions, which impacts on the durability and service life of the structures. In this paper, site data was gathered, which was used to perform a numerical and a finite element modelling to investigate the impacts of several conditions on thermal cracking in a structure. The field recorded data was used for the numerical modelling, using MATLAB software, and the finite element modelling, using ANSYS Mechanical software. It was observed that among the conditions considered, the wall ratio in the structure and formation of microcracks have significant impacts, while the age of the structure, the compressive strength of the concrete have minimal impacts, as the shifting in the curve is small. Finally, a probabilistic crack development model was made to study the potential crack development in the finite element model, which was seen to tally with observed site data, demonstrating the potential of predicting cracks development.

Prevention in Thermal Crack Formation in Chabazite (CHA) Zeolite Membrane by Developing Thin Top Zeolite and Thick Intermediate Layers

Chabazite (CHA) zeolite membranes with an intermediate layer of various thicknesses were prepared using planetary-milled seeds with an average particle diameter of 300, 250, 200, 140, and 120 nm. The 120 nm seed sample also contained several smaller particles with a diameter of 20 nm. Such small seeds deeply penetrated into the pore channels of the α-alumina support during the vacuum-assisted infiltration process. During the secondary growth, the penetrated seeds formed a thick intermediate layer exiting between the zeolite layer and support. A decrease in seed size increased the penetration depth of seeds and the thickness of the intermediate layer, while the thickness of seed coating and zeolite layers was decreased. CHA zeolite membranes with a thin top zeoliate layer and a thick intermediate layer showed an excellent water/ethanol separation factor (>10,000) for 90 wt.% ethanol at 70 ℃ with a total flux of 1.5 kg m−2 h−1. There was no observation of thermal cracks/defects on the zeolite separation layer. The thick intermediate layer effectively suppressed the formation of thermal cracks during heating, since the tensile stress induced in the zeolite layer was well compensated by the compressive stress on the support. Therefore, it was successfully proven that controlling the microstructure of top surface and intermediate layers is an effective approach to improve the thermal stability of the CHA zeolite membrane.

Numerical Study on Thermal Damage Behavior and Heat Insulation Protection in a High-Temperature Tunnel

Deepening our understanding of temperature and stress evolution in high-temperature tunnels is indispensable for tunnel support and associated disaster prevention as the rock temperature is remarkably high in hot dry rock (HDR) utilization and similar tunnel engineering. In this paper, we established a two-dimensional thermal–mechanical coupling model through RFPA2D-thermal, by which the temperature and stress field of the surrounding rock in a high-temperature tunnel with and without thermal insulation layer (TIL) were studied, followed by the evolution of thermal cracks. The associated sensitivity analysis of the TIL and airflow factors were then carried out. We found that (1) the tunnel rock is unevenly cooled down by the cold airflow, which induces thermal stress and damages the rock element when it exceeds the tensile strength of the rock mass. Those damaged rock elements accumulate and coalesce into visible cracks in the tunnel rock as the ventilation time goes, reducing the tunnel stability. (2) TIL effectively reduces the heat exchange between the airflow and tunnel rock and weakens the cold shock by the airflow, delaying the crack initiation which provides efficient time to adopt engineering measures for tunnel supporting. (3) TIL parameters are of pivotal importance to the long-term cold shock by the airflow. Increasing the TIL thickness and reducing the TIL thermal conductivity both significantly enhance the thermal insulation effect. The results cover the gap in the study of cold shock in high-temperature tunnels, which is helpful in designs to prevent thermal damage in high-temperature tunnels.

In vitro biological and antimicrobial properties of chitosan-based bioceramic coatings on zirconium

Ca-based porous and rough bioceramic surfaces were coated onto zirconium by micro-arc oxidation (MAO). Subsequently, the MAO-coated zirconium surfaces were covered with an antimicrobial chitosan layer via the dip coating method to develop an antimicrobial, bioactive, and biocompatible composite biopolymer and bioceramic layer for implant applications. Cubic ZrO2, metastable Ca0.15Zr0.85O1.85, and Ca3(PO4)2 were detected on the MAO surface by powder-XRD. The existence of chitosan on the MAO-coated Zr surfaces was verified by FTIR. The micropores and thermal cracks on the bioceramic MAO surface were sealed using a chitosan coating, where the MAO surface was porous and rough. All elements such as Zr, O, Ca, P, and C were homogenously distributed across both surfaces. Moreover, both surfaces indicated hydrophobic properties. However, the contact angle of the MAO surface was lower than that of the chitosan-based MAO surface. In vitro bioactivity on both surfaces was investigated via XRD, SEM, and EDX analyses post-immersion in simulated body fluid (SBF) for 14 days. In vitro bioactivity was significantly enhanced on the chitosan-based MAO surface with respect to the MAO surface. In vitro microbial adhesions on the chitosan-based MAO surfaces were lower than the MAO surfaces for Staphylococcus aureus and Escherichia coli.

Thermo-Mechanical Simulation of Ti6Al4V-NiTi Dissimilar Laser Welding Process

Fiber Laser Welding (FLW) is a versatile joining technique of metals and alloys because it allows welding of dissimilar materials without filler material. FLW utilizes intensified heat energy to liquify the workpiece interface and joins when they are solidified. In this study, dissimilar joining between Ti6Al4V-Nitinol was performed using FLW process and the thermomechanical model was developed to understand the metallurgical mechanisms and investigate weldability of dissimilar alloys. The FLW of Ti6Al4V and Nitinol plates was performed with variable power density, welding speed, and focal distance. In this three-dimensional numerical model, heat flows in two different workpieces were computed during active laser welding and cooling process using a combined effect of radiation and convection. Both of the top and bottom surfaces of the welded zone were studied considering the combined effect from focused heat source and Argon shielding gas. Significant thermal cracks were produced through the welded interface. However, this numerical study illustrated thermomechanical foundation and discuss future challenges to improve the integrity and desirable FLW parameters in the dissimilar metal joining.