ABSTRACT
A milling force measurement tool system is designed with an elastic beam structure, which is divided into a two-end ring hoop compression sensor mode and a two-end square hoop compression sensor mode to improve the strain sensitivity. A simplified mechanical model of the elastic beam is established, and the relationship between the strain and force of the elastic beam under the action of three cutting force components is investigated, which can act a guide for subsequent milling force measurement tool system calibration tests. Thin-film strain sensors occupy a central position in the milling force measurement tool system, which consists of a substrate, transition layer, insulating layer and resistance grid layer. The resistance grid layer has a particularly significant effect on the thin-film strain sensor's performance. In order to further improve the sensitivity of thin-film strain sensors, the shapes of the substrate, the transition layer, the insulating layer and the resistance grid layer are optimized and studied. A new thin-film strain sensor is designed with a resistance grid beam constructed from an insulating layer and a resistive grid layer double-end-supported on the transition layer. The flow of the wet-etching process of thin-film strain sensors is studied and samples are obtained. The surface microforms of the sensor samples are observed by extended depth-of-field microscopy, confocal microscopy and atomic force microscopy. It can be seen that the boundary of the resistance grid layer pattern is tidy and has high dimensional accuracy, thus enabling the basic achievement of the expected effect of the design. The electrical performance of the samples is tested on an experimental platform that we built, and the results show that the resistive sensitivity coefficient of the samples is increased by about 20%, to 51.2%, compared with that of the flat thin-film strain sensor, which fulfils the design's requirements.
ABSTRACT
The Johnson-Cook (J-C) constitutive model is not suitable for Ti-6Al-4V alloy in the high-speed cutting finite element simulation, as it has no response dynamic recrystallization softening effect under heavy impact and high temperature. In this paper, an improved constitutive model considering the recrystallization effect was established, and the parameters were fitted with the data of flow stress-strain of the Split Hopkinson Pressure Bar (SHPB) test. The relevant theories of cutting finite element simulation were studied, such as nonlinear constitutive elastic-plastic deformation, strain state, and material yield. A subroutine that included the Recht shear failure instability criterion and the improved model was coded in Fortran and embedded in the finite element simulation software AdvantEdge FEM, along with the return mapping stress integration algorithm. The simulated stress of the improved model dropped dramatically from 460 MPa to 220 MPa when the temperature rises from 950 °C to 1000 °C, and its decline reached 46.7%, while the J-C model only decreased by 10%. Comparative studies indicate that the stress change of the improved constitutive simulation is closer to the SHPB test results than the J-C constitutive, and the new one is more suitable when it expresses the high temperature and heavy impact in the high-speed milling.
ABSTRACT
With the intelligent tool cutting force measurement model as the engineering background, the selection, design, and optimization of the substrate structure of the tool-embedded thin-film strain sensor are studied. The structure of the thin-film strain sensor is studied, and the substrate structure design is divided into function area structure design and connection area structure design. Establishing the substrate structure library of the sensor, we subdivide the library into six layouts of function area infrastructure and five layouts of connection area infrastructure. Taking the sensitivity, fatigue life, and comprehensive mechanical properties of the substrate structure as the design indexes, based on the statics theory, the functional relationship between the structural parameters and the deflection of the six layouts of the substrate function area is established; based on the dynamics theory, the functional relationship between the parameters and the natural frequency of six layouts of the function area is established; based on the coupling of structural statics design theory and dynamics design theory, the evaluation method for the comprehensive performance of the parameters of six layouts of the function area is established. Based on the function area structure, five connection area structures are designed for comprehensive performance analysis. The structural sensitivity of the substrate function area design and optimization is expanded 1.75 times, and the comprehensive performance is expanded 1.53 times. The sensitivity of the connection area design and optimization is expanded 2.3 times, and the comprehensive performance is expanded 1.72 times. The structure is optimized according to the structural stress characteristics, the design, selection, and optimization process of the substrate structure summarized herein, and five design criteria of the substrate structure are proposed.
ABSTRACT
A thin-film strain micro-sensor is a cutting force sensor that can be integrated with tools. Its elastic substrate is an important intermediate to transfer the strain generated by the tools during cutting to the resistance-grid-sensitive layer. In this paper, 1060 aluminum is selected as the elastic substrate material and aluminum oxide thin film is selected as the transition layer between the aluminum substrate and the silicon nitride insulating layer. The Stoney correction formula applicable to the residual stress of the aluminum oxide film is derived, and the residual stress of the aluminum oxide film on the aluminum substrate is obtained. The influence of Sputtering pressure, argon flow and negative substrate bias process parameters on the surface quality and sputtering power of the aluminum oxide thin film is discussed. The relationship model between process parameters, surface roughness, and sputtering rate of thin films is established. The sputtering process parameters for preparing an aluminum oxide thin film are optimized. The micro-surface quality of the aluminum oxide thin film obtained before and after the optimization of the process parameters and the surface quality of Si3N4 thin film sputtered on alumina thin film before and after the optimization are compared. It is verified that the optimized process parameters of aluminum oxide film as a transition layer can improve the adhesion between the insulating-layer silicon nitride film and the aluminum substrate.
ABSTRACT
The thin-film strain sensor is a cutting-force sensor that can be integrated with cutting tools. The quality of the alloy film strain layer resistance grid plays an important role in the performance of the sensor. In this paper, the two film patterning processes of photolithography magnetron sputtering and photolithography ion beam etching are compared, and the effects of the geometric size of the thin-film resistance grid on the resistance value and resistance strain coefficient of the thin film are compared and analyzed. Through orthogonal experiments of incident angle, argon flow rate, and substrate negative bias in the ion beam etching process parameters, the effects of the process parameters on photoresist stripping quality, etching rate, surface roughness, and resistivity are discussed. The effects of process parameters on etching rate, surface roughness, and resistivity are analyzed by the range method. The effect of substrate temperature on the preparation of Ni Cr alloy films is observed by scanning electron microscope. The surface morphology of the films before and after ion beam etching is observed by atomic force microscope. The influence of the lithography process on the surface quality of the film is discussed, and the etching process parameters are optimized.
ABSTRACT
Thin-film strain sensors are widely used because of their small volume, fast strain response and high measurement accuracy. Among them, the thin-film material and preparation process of thin-film strain sensors for force measurement are important aspects. In this paper, the preparation process parameters of the transition layer, insulating layer and Ni-Cr alloy layer in a thin-film strain sensor are analyzed and optimized, and the influence of each process parameter on the properties of the thin film are discussed. The surface microstructure of the insulating layer with Al2O3 or Si3N4 transition layers and the film without transition layer were observed by atomic force microscopy. It is analyzed that adding a transition layer between the stainless steel substrate and insulation layer can improve the adhesion and flatness of the insulation layer. The effects of process parameters on elastic modulus, nanohardness and strain sensitivity coefficient of the Ni-Cr resistance layer are discussed, and electrical parameters such as the resistance strain coefficient are analyzed and characterized. The static calibration of the thin-film strain sensor is carried out, and the relationship between the strain value and the output voltage is obtained. The results show that the thin-film strain sensor can obtain the strain generated by the cutting tool and transform it into an electrical signal with good linearity through the bridge, accurately measuring the cutting force.
ABSTRACT
The measurement of cutting force is an effective method for machining condition monitoring in intelligent manufacturing. Titanium nitride films and silicon nitride films were prepared on 304 stainless steel substrates by DC-reactive magnetron sputtering and plasma-enhanced chemical vapor deposition (PECVD). The effects of substrate negative bias and nitrogen flow on the surface microstructures of TiN film were investigated. The smoothness of the film is optimal when the bias voltage is -60 V. X-ray diffraction (XRD) analysis was performed on the samples with the optimal smoothness, and it was found that when the nitrogen flow rate was higher than 2 sccm, the titanium nitride film had a mixed phase of TiN(111) and (200). It is further revealed that the change of peak intensity of TiN(200) can be enhanced by nitrogen flow. Through atomic force microscopy (AFM), it is found that the stronger the intensity of the TiN (200) peak, the smoother the surface of the film is. Finally, the effect of different film thicknesses on the hardness and toughness of the TiN/Si3N4 film system was studied by nanoindentation experiments. The nanohardness (H) of the TiN/Si3N4 film can reach 39.2 GPa, the elastic modulus (E) is 480.4 GPa, the optimal toughness value (H3/E2) is 0.261 GPa, and the sample has good insulation performance. Linear fitting of the film's toughness to nanohardness shows that TiN/Si3N4 films with higher hardness usually have a higher H3/E2 ratio.
ABSTRACT
Isoflurane is a broadly used inhalation anesthetic that causes cognitive impairment in rodent models as well as humans. Although previous studies suggested an association between isoflurane exposure and neuro-inflammation, apoptosis and mitochondrial dysfunction, the pathogenesis of isoflurane-induced cognitive decline remains elusive. In the present study, 22-month-old male Sprague-Dawley male rats (n=96) were divided into three groups: Control (Cont), isoflurane (ISO) and MS-275 pre-treated groups. The rats were sacrificed following exposure to isoflurane and a cognitive test. The hippocampus of each animal was harvested for quantitative PCR, TUNEL staining and western blot analysis. Histone deacetylases (HDAC)-1, -2 and -3 exhibited a significant increase at the gene and protein expression levels, whereas negligible mRNA expressions were observed for genes HDAC 4-11 (P>0.05; compared with Cont). Pre-treatment with the HDAC inhibitor MS-275 significantly inhibited the increase in TUNEL-positive cells induced by isoflurane exposure (70.72% decrease; P<0.001; compared with ISO). Furthermore, MS-275 significantly decreased caspase-3 and Bax expression levels while increasing Bcl-2 protein expression. The isoflurane-induced changes in the MAPK pathway signaling proteins ERK1/2, JNK and p38 were also reversed with MS-275 pre-treatment. Finally, in a Morris water maze test, the time to find a hidden platform was reduced in MS-275 pre-treated rats, compared with the ISO group. Therefore, the present study provided insight into the effect of isoflurane exposure on neuronal apoptosis pathways, as well as cognitive decline via epigenetic programming of MAPK signaling in aged rats.
ABSTRACT
Adhesion is a major factor in film failure. Based on the basic theory of interfacial toughness, the relationship between film thickness and internal stress and adhesion is qualitatively analyzed. The adhesive properties of silicon nitride deposited on stainless steel substrate by plasma enhanced chemical vapor deposition methods is discussed. The case where nickel, nickel-chromium and alumina films are respectively used as transition layers is compared. After vacuum annealing thermal treatment of these films, the results show that the alumina film has better matching performance with 304 stainless steel, and the interface toughness is improved by 51.2% compared with the silicon nitride film. After the samples are stretched, the silicon nitride film show a large number of cracks when the transition layer is nickel or nickel-chromium, possibly due to the large thermal stress in the film. At the same time, the process parameters of magnetron sputtered alumina are optimized, and the optimal deposition rate of alumina film is determined to be 40.25 nm min-1. Then, the effect of film thickness on adhesion is investigated by theoretical analysis and tape breakage test. As the film thickness ratio of alumina and silicon nitride increases, the adhesion is optimal.
ABSTRACT
This paper proposes a high-strain sensitivity turning dynamometer that combines several thin-film resistor grids into three Wheatstone full-bridge circuits that can measure triaxial cutting forces. This dynamometer can replace different cutter heads using flange connections. In order to improve the strain effect of the dynamometer, the strain film sensor is fixed on the regular octagonal connection plates on both ends of the elastomer by vacuum brazing, and the stepped groove structure is also designed inside the elastomer. The dynamometer model is simplified as a four-segment cantilever beam which has different sections. The measurement mechanism model of the dynamometer system is established by the transformation relationship between deflection and strain, under external force. The standard turning tool of 20 mm square is used as a reference. The influence of the structural dimensions of the dynamometer on its strain sensitivity coefficient K is studied. The applicability of the theoretical model of dynamometer strain is verified by finite element analysis. Finally, the dynamometer with the largest K value is subjected to the bending test and compared with a standard turning tool. The experimental results show that the measurement sensitivity of the dynamometer is 2.32 times greater than that of the standard turning tool. The results also show that this dynamometer can effectively avoid the influence of the pasting process on strain transmission, thus indicating its great potential for measuring cutting force in the future.
