Grinding Crack Research Articles

Research on Crack Mechanism of Surface/Subsurface Based on Grinding Stress Field in Ultrasonic Grinding Nano-Ceramics

The crack nucleation and propagation process in ultrasonic grinding engineering ceramics are studied based on indentation fracture mechanics. The study shows ultrasonic grinding can be considered as continuous loading and unloading process in view of a single grain. The loading makes cracks form and preliminarily propagate; while the unloading makes them propagate further and makes the direction of crack propagation offset to the workpiece surface, not so far as to extend to the material interior. In common grinding cracks have extended to the material interior, resulting in deep subsurface crack in the subsurface layers. In this paper, the ground surface of small crack damage can be obtained with large grinding depth in ultrasonic grinding compared with common grinding under the same conditions.

Grinding force and crack size on through-hole drilling of glass plate used electroplated diamond tool in helical drilling

Grinding force and crack size on through-hole drilling of glass plate used electroplated diamond tool in helical drilling

Study on the Ceramic Grinding Crack Propagation Mechanism under the Ultrasonic Action by Using Nonlocal Theory

This paper presents a research on the attenuation of cyclic stress amplitude and the variation of microstructure under the action of ultrasonic vibration in crack propagation for Al2O3-ZrO2 composite nano-ceramics. To interpret this phenomenon, the nonlocal theory is introduced to establish the constitutive model under the ultrasonic condition based on the specified 2D attenuating function. The mechanics behavior of the ceramics under the action of ultrasonic vibration is analyzed according to the relationship between the internal character length and the external character length (i.e. ultrasonic wave length). In addition, the variation law of the cyclic stress amplitude and microstructure with different ultrasonic frequencies is also studied in this paper. It is shown that the cyclic stress amplitude is attenuated under the action of ultrasonic vibration, and this attenuation phenomenon becomes more and more evident by increasing the ultrasonic frequency. The results of experiment are in accordance with the theoretical conclusions drawn from the nonlocal theory, which verifies that the action of ultrasonic vibration can actually accelerate the ceramic crack propagation.

Tribological Behavior of Nano-Silicate Mineral Powder as Lubrication Oil Additive

The tribological behavior and the mechanism of nano-silicate mineral powder as lubrication oil additive were researched in the article. The tribological behavior of nano-silicate mineral powder with mass ratio 0.6% in lubrication oil 50CC was tested and compared with the lubrication oil 50CC’s by friction wear testing machine. The surface morphologies and elementary compositions of grinding cracks were analyzed by Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS).The results showed that the friction coefficient is decreased 37.5%, and the lost mass of the upper proof sample reduces 68.75%, the down’s reduces 86.7%, after adding nano-silicate mineral as lubrication oil additive, by comparison to lubrication oil 50CC’s. Under the lubrication oil which has been putted nano-silicate mineral as additive, there is a repairing layer whose material is different from basal body material on the grinding cracks; in addition, Si, Mg and other elements are deposited on the repairing layer. These state that nano-silicate mineral as lubrication oil additive possesses superior behavior of wear resistance, antiwear and self-repairing effects.

Cracking in cargo aircraft main landing gear truck beams due to abusive grinding following chromium plating

While a wheel was being replaced on the subject aircraft, a crack was found on the rear axle bore of the left-hand main landing gear truck beam. This part had been overhauled 11 months earlier. One year later, while the subject aircraft was being parked, two loud bangs were heard coming from the right-hand main landing gear. Upon inspection, the right-hand truck beam was found cracked longitudinally at two locations on the rear axle bore. Microscopic examination revealed two crack origins, one on each side of the bore. Both cracks propagated from corrosion pits under the chromium plating in a stable intergranular mechanism. The final overload fracture produced quasi-cleavage features. Nital etch, following removal of the chromium plating, revealed areas of overtempered and untempered martensite indicative of heat damage incurred during abusive grinding. The hardness of the material in the heat-affected areas and in the areas adjacent to the origins was lower than that of the surrounding tempered martensite structure. These heat-affected areas were located in the chromium plating runout plateau adjacent to the counterbore transition radius and exhibited numerous thermally induced secondary cracks. It was concluded that the cause of failure was improper overhaul process, which left grinding burns and cracks beneath the chromium coating. Subsequently, electrolyte that penetrated through these cracks promoted the formation of pits beneath the coating, which served as preferred sites for failure initiation.

Research on materials of piston and cylinder of water hydraulic pump

In this paper, experiments were carried out to study the friction and wear performance for the materials of the piston and cylinder in a water hydraulic axial piston pump. The matching of a 940 stainless steel circle with a F102 engineering plastics block and a 940 stainless steel circle with an Al2O3 ceramic block were also studied. The wearing capacities were calculated by theoretical formulae based on the grinding crack widths. When pure water is used as hydraulic transmission medium, it is better to use ceramic with engineering plastics as matching materials for the piston and cylinder of water hydraulic axial piston pump. The experimental results have provided a theoretical basis for selecting the matching materials of the piston and cylinder.

Effect of grinding temperatures on the surface integrity of a nickel-based superalloy

An experimental study was carried out to investigate the influence of temperatures on workpiece surface integrity in the surface grinding of a cast nickel-based superalloy with alumina abrasive wheels. The temperature response at the wheel–workpiece interface was measured using a grindable foil/workpiece thermocouple. Specimens with different grinding temperatures were obtained through changing the grinding conditions, including the depth of cut, the workpiece feed, and the coolant supply. Changes in the surface roughness, residual stress, metallography, ground surface morphology, and micro-hardness of the specimens were then analyzed. Bending fatigue tests were separately conducted at room temperature and at 950 °C in order to evaluate the influence of temperatures on the service life of the ground specimens. A different burning color was found on the ground workpiece surfaces when grinding temperatures are over a critical value. Along with the emergence of a burning color, the roughness of the ground workpiece surface increased greatly compared with the surfaces without burning color, which was attributed to plastically deformed coatings on the workpiece surface occurring with elevated temperatures. Excepting the surface roughness, surface integrity of the ground workpiece was not affected by temperature, provided that grinding temperature is not high enough to cause grinding cracks. Based on the findings in this study, the grinding of nickel-based superalloy can be divided into two stages in order to increase production efficiency, in which case the first stage is to reach high material removal rate without concern for the presence of a burning color, whereas the second stage is to remove the plastically deformed coatings in order to decrease the surface roughness.

Study of the Formation and Propagation Conditions of Grinding Crack for Ceramics

Study of the Formation and Propagation Conditions of Grinding Crack for Ceramics

Analysis of the causes of the appearance of brittle cracks in large stamped preforms from steel 30KhGSNMA-VD

1. Intermediate annealing after stamping large preforms of steel 30KhGSNMA-VD can be accompanied by temper brittleness of kind II, which causes the formation of brittle cracks in subsequent grinding and quenching. 2. In order to prevent the formation of brittle cracks in stamped preforms, they should be subjected to sandblasting after grinding and decelerated heating for quenching in the final treatment.

Near‐Surface Deformation in an Alumina–Silicon Carbide‐Whisker Composite due to Surface Machining

Deformation due to two different surface‐machining conditions—grinding (126 μm diamond) and polishing (3 μm diamond)—in an uniaxial hot‐pressed Al2O3–30%‐SiC‐whisker composite has been investigated. A Warren–Averbach analysis of grazing incidence X‐ray diffractometry data shows that the deformation is localized to the very top surface zone. The cell size and the root mean square of the strain show a gradient in the deformed layer. Transmission electron microscopy studies, in cross‐sectional view, also show a near‐surface deformation zone containing dislocations, twins, and cracks. This is seen for both machining procedures, but the depth of the zone and the degree of deformation, in terms of dislocation density and number of cracks, is much higher in the roughly ground specimen than in the polished one. For comparison, a monolithic Al2O3 sample also has been studied after grinding. The deformation zone is very similar to the Al2O3–SiC sample with the same grinding condition, but cracks and dislocations are present at a slightly larger depth. The deformation depth for the polished Al2O3–SiC sample is ∼50 nm. In the ground Al2O3–SiC sample, the deformation depth is 1–1.5 μm and corresponds to the grain size. The deformation zone in the ground monolithic Al2O3 sample is 1.5–2 μm deep. The observed grain‐boundary cracks are almost parallel to the surface and may originate from nonaccommodated plastic flow between grains.

温式および乾式研削されたジルコニアの曲げ強度

Specimens of tetragonal zirconia containing 3mol% Y2O3 were ground wetly and dryly with a grinding wheel of grain size 200/230. The residual stress and the monoclinic content were measured by the X-ray diffraction method. The monoclinic content on the surface ground wetly with enough coolant was raised to about 7 percent. For wet ground Y-TZP, bending stress was applied in directions parallel and perpendicular to the grinding direction. The bending strength in both directions increased because of compressive residual stress. Fracture did not start from grinding cracks. For Y-TZP ground dryly without coolant, the bending stress was applied in the direction pallaled to the grinding direction. Many grinding cracks were introduced on the ground surface and no compressive residual stress was measured. Since the ground surface was heated to a high temperature, the transformation to the monoclinic phase did not occur. The bending strength of dry-ground Y-TZP was reduced remarkably. The breadth of X-ray line broadening measured on the dry-ground furface was larger than that of the wet-ground surface. The depth of the grinding-affected zone was 10μm for the dry-ground surface and 30μm for the wet-ground surface.

研削割れに与える研削油剤の影響 クリープフィード研削時の研削割れに関する研究

In creep feed grinding, the grinding cracks are generated by heat. It has been known by experience that the grinding fluids influence on grinding cracks. Grinding fluids are generally used for cooling and lubrication. To evaluate the properties of grinding fluids, the temperature at the grinding point, cooling rate of work material and load carrying capacity of grinding fluids were checked. Finally it was clarified that a gentle slope of cooling could relieve the grinding cracks and high load carrying capacity of grinding fluid was not effective.

In process detection of grinding cracks in fine ceramics by the use of acoustic emissions.

A method of detecting grinding cracks during the grinding process has not yet been developed in fine ceramics. The objective of this study is to example whether grinding cracks, which are generated during the grinding process, can be detected in-process by monitoring the acoustic emission AE. AE signals, which were detected during grinding, have been analyzed and compared with the signal before grinding cracks are generated. AE between 1.0 - 1.2 MHz are detected when grinding cracks are generated, while they are not detected when grinding cracks are not generated in fine ceramics. By utilizing this relationship. it becomes possible to detect grinding cracks in-process.

Effect of one Pass Grinding on the Initiation of Fatigue Crack

The effect of one pass grinding on the initiation of fatigue cracks was studied using a low carbon steel. It was found that the so-called grinding cracks (caused by the thermal stress) and the cracks initiated by abrasive grains imbedded into the steel can be the origin of the fatigue cracks. More-over, there is a strong possibility that a piling up of dislocations against an obstacle like a grain boundary gave birth to the fatigue cracks. These two processes may cause cracking during the grinding. It was also found that, besides the usual grinding conditions, the grinding direction to the specimen axis affected the mode of fatigue crack initiation.

THREE-DIMENSIONAL THERMAL DEFORMATION AND THERMAL STRESS IN WORKPIECES UNDER SURFACE GRINDING

The three-dimensional distribution of temperature, thermal deformation, and thermal stress in a workpiece during table traverse cross-feed surface grinding is computed numerically, and the effects on the dimensional accuracy, the holding force of the magnetic chuck, and the grinding cracks in the workpiece are discussed. The temperature distribution is calculated by a finite-difference method, and the distribution of thermal deformation and thermal stress is determined by a numerical method developed from the relaxation method. From the results of the analysis, it is clear that the deformation of workpieces cannot be disregarded when considering dimensional accuracy, and that the magnetic chuck is not sufficient to counteract the thermal bending of the workpiece.

マルテンサイト鋼の研削き裂の生成機構(第2報)

マルテンサイト鋼の研削き裂の生成機構(第2報)

研削き裂起源に対するマルテンサイト晶の衝突き裂とひずみの存在意義

The grinding cracks are frequently found in the medium and high carbon martensite steels such as Fe-C steels, bearing steels, Mo steels, Mn steels, Ni steels and Cr steels. We are decided to go back to the metal structure in the origin of the workpiece to observe the grinding cracks from metallographical standpoint. In this report, the first step of study is investigated the kern and origin of the grinding cracks in the martensite structure. The next step deals with the significance of existence for the grinding cracks of martensite impingement cracks and the shape or size of the minimum unit of it. A summary of the main results are shown below.(1) The impingement cracks of martensite were observed the lenticular martensite in the many shape of it. And the impingement cracks were become frequently kern of grinding cracks.(2) The combination of martensite's impingement cracks and grinding cracks were observed in many kinds of the workpiece.(3) The generation of minimum unit size of grinding cracks are observed in the martensite crystal. And the length of it was shown very high frequency in the range of 4.0-5.0μm.(4) The stain and impingement cracks of martensite is very high sensitivity of the notch effect or stress concentration.(5) The generation of microcrack in γ-phase was not observed in the transformation from fcc to bct.

鋼材の研削焼けおよび研削割れ

On the grinding work we have previously seen a few investigations, but all of them was limited to inspect only from the side of steel under the grinding. The present authors recognized that failures of grinding work were caused (induced) from mutual relations of the condition of grinding work and steel under the grinding, and, therefore, inspected from both sides of them, and chiefly on bearing steel. On the experiment has been carried out several inspections by the conditions determined previously from the grinding work and obtained experimentally from the limit depth of cut to which the grinding burn on grinding crack occurred on the surface of steel. We could recognize that the formation of failure was dependent on grinding heat which is affected by conditions of the grinding work or the properties of steel under the grinding. The results were as follows: (1) On the grinding burn of various steels, the limit depth of cut of quenched steels is smaller than that of annealed one. (2) Thermal diffusion in the steel under the grinding is smaller, the more sensible grinding burn or grinding crack is. (3) Tempering temperature of the steel after quenching is higher, the less the formation of grinding burn or crack occurs. (4) In case of low tempering treatment, grinding crack precedes to grinding burn, but in case of high tempering treatment, this aspect becomes opposite. (5) Against several phenomena mentioned above, we carried out theoretical investigation from both sides of the grinding work and of the steel.

熱間圧延せる硬質条鋼の側面中心部の裂疵および研磨割れならびに焼割れの生因について

熱間圧延せる硬質条鋼の側面中心部の裂疵および研磨割れならびに焼割れの生因について