369 results about "Fatigue crack propagation" patented technology

The invention discloses a prescription of a wheeltrack lubricant additive, which is characterized by strong bearing capacity, high temperature resistance and long effective time upon one time coating, thereby solving the defect that factigue crack expansion of the wheeltrack is accelerated by traditional grease for the generation of oil wedge effect. The prescription comprises 1 percent-30 percent of metal powder, 3 percent-50 percent of high temperature solid lubricant material and 5 percent-50 percent of fatty acid by weight. The strip solid materials can be produced in virtue of other accessories by the prescription.

The invention provides a dynamic crack length measurement method for a fatigue crack propagation test based on the machine vision technology. The method comprises the following steps: 1, performing machine vision crack measurement system calibration; 2, performing fatigue test, wherein a test piece with precracks begins to generate fatigue cracks along the direction of the precracks, and the fatigue cracks extend; 3, collecting crack images, wherein a mode of collecting single-face images of the test piece and a mode of collecting two-side images of the test piece are used in the fatigue crack propagation test; 4, reinforcing the collected images; 5, identifying the position of the trunk of cracks, as well as peaks and identifying directions of cracks by using the method of image analysis and crack identification; and 6, calculating the actual crack identifying length and crack length. The method has the advantages of simplifying the process and reducing work load; and by the method, the crack identifying process can be visually and accurately observed and recorded, the calculated crack length specified by the international standard can be measured accurately. The method also has the advantages of high measurement accuracy and good system anti-jamming performance.

The invention relates to a camera automatic regulating crack image acquisition system for a fatigue crack propagation test, which comprises a crack image imaging and acquiring system, a camera position regulating system and a computer processing and analysis control system, wherein the crack image imaging and acquiring system comprises a CCD (Charge Coupled Device) camera, a lens, a light source illuminating device, a camera mounting bracket and an image acquiring card; the CCD camera, the lens and the light source illuminating device are arranged on the camera mounting bracket to form a crack image imaging unit; the image acquiring card is connected with a computer; a camera position regulating device comprises a stepping motor, a camera motion positioning cloud deck, a motion controller and a stepping motor driver; and the computer processing and analysis control system comprise the computer and a camera automatic regulating image acquisition module in an ARM motion controller. The invention also provides a camera automatic regulating crack image acquisition method for the fatigue crack propagation test. According to the camera automatic regulating image acquisition device and method for fatigue crack propagation test provided by the invention, the full-automatic operation is adopted; the control accuracy is high; and the real-time performance is excellent; and the labor intensity is reduced.

The invention discloses a method for evaluating the fatigue life of an aged reinforced concrete bridge. The method comprises the following steps of obtaining initial corrosion time of reinforcement in concrete based on the second diffusion law of Fick, and considering the influence of concrete cracking due to corrosion expansion in a corrosion rate model; adopting a small crack growth and near threshold growth analysis and determining relevant parameters of fatigue crack propagation rate of materials by developing a fatigue crack propagation test of reinforced concrete materials; performing a corrosion fatigue test or finite element analysis on corroded reinforcement to obtain stress concentration factors at different corrosion levels, and integrating into a stress intensity factor model to obtain the fatigue crack propagation rate of the reinforcement under the influence of corrosion; comparing the magnitude of a corrosion pit growth rate and the fatigue crack propagation rate and gradually converting into a single growth analysis on fatigue cracks of the reinforcement; meanwhile, combining with vehicle load observing information to realize life evaluation of a bridge at different service stages. The prediction method disclosed by the invention is reasonable and high in popularization, and can provide technical support for evaluating the life of the concrete bridges.

A crack growth rate and crack growth life prediction method for a mechanical structure belongs to a calculation method for fatigue crack growth rate and crack growth length of the mechanical structure. At first, a relationship between S-N and P-S-N curve expressions (power function form) and a crack growth rate curve expression (Paris formula) is built up in the method. A determination method of the crack growth rate under the conditions of block spectrum load, overload hysteresis load and random load is proposed. And a determination method of Paris curve parameters is provided when the S-N and P-S-N curves cannot be expressed in power function form. And a method for improving the prediction precision of the crack growth rate and the crack growth life is proposed. The S-N and P-S-N curves are used by the method to predict the crack growth rate and the crack growth life. Therefore, the method has the advantages of little dependence on tests and high precision and can shorten the product development period and save much manpower, material resources and financial resources.

The invention provides a gear bending fatigue life forecast method and a device. The gear bending fatigue life forecast method comprises the steps that a fatigue limit amendment model is built based on the surface roughness, and the fatigue limit of materials is amended according to the amendment model, the fatigue limit after the amendment is obtained; the threshold crack length is determined according to the threshold stress strength factor range and the amended fatigue limit; a fatigue crack size initiation model is created, and gear fatigue crack initiation life is forecasted based on the fatigue crack size initiation model; gear fatigue crack propagation life is forecasted based on the linear elastic fracture mechanics guidelines; according to the gear fatigue crack initiation life and gear fatigue crack propagation life, a gear bending fatigue calculation model is built, to calculate the gear bending fatigue life.

A gamma prime nickel-base superalloy and components formed therefrom that exhibit improved high-temperature dwell capabilities, including creep and dwell fatigue crack growth behavior. The superalloy contains, by weight, 10.00 to 22.0% cobalt, 10.0 to 14.0% chromium, 4.0 to 6.0% tantalum, 2.0 to 4.0% aluminum, 2.0 to 6.0% titanium, 1.5 to 5.0% tungsten, 1.5 to 5.0% molybdenum, 1.0 to 3.5% niobium, 0.05 to 0.6% hafnium, 0.02 to 0.10% carbon, 0.01 to 0.40% boron, 0.02 to 0.10% zirconium, the balance essentially nickel and impurities, wherein the titanium:aluminum weight ratio is 0.7 to 1.5. The superalloy is hot worked and heat treated to contain cellular gamma prime precipitates that distort grain boundaries, creating tortuous grain boundary fracture paths that are believed to promote the fatigue crack growth resistance of the superalloy.

The invention discloses a method for measuring fracture toughness of pipeline steel by using a unilateral notched tensile test. The method is characterized by comprising the steps of preparing a unilateral notched tensile test sample; prefabricating a tensile sample crack by wire-electrode cutting and fatigue crack growth rate test method; calculating crack growth amount according to the tensile sample cracks; and acquiring J integration and stress intensity factor K for characterizing the fracture toughness of the pipeline steel by drawing a J-R curve for characterizing crack resistance of the crack growth. The method measures the fracture toughness of the pipeline steel by using tensile samples (SENT samples), overcomes the defects that the scope of measurement results of tensile samples (SENT samples) by a conventional technology is so small that the fracture toughness of the pipeline steel can not be evaluated; the crack toughness value of the tensile samples (SENT samples) can be more reasonable; waste of test for pipeline steel materials can be prevented; and the method has the advantages of high measurement accuracy.

The invention relates to a test system and a test method for the dynamic bending fatigue property of a small-scale thin film material. The test system comprises an electromagnetic driving part, a sample holding part and a measuring and observing part, and the system provides functions and a test method for dynamic bending fatigue property test for the thin film materials used for various micro/nanoelectronic mechanical systems and supported with matrix or without matrix, the metalized interlinking body foil material used for an integrated circuit and various two-dimensional thin plate type materials and can record in-situ real-time monitoring and analysis to the appearance of the tested sample. The free end of the cantilever beam sample is driven under the electromagnetic force of the electrified coil in the stationary magnetic field to reciprocate relatively to the equilibrium position thereof, thus various types of cyclic fatigue loads can be applied to various material samples, and the precision of the applied fatigue loads can reach the millinewton magnitude. The invention can be used to evaluate the fatigue property and the fatigue crack growth behaviors of various thin film materials.

The invention discloses a method capable of carrying out fatigue crack propagation rate estimation and life prediction. The method comprises the following steps: (1) carrying out a fatigue crack test, and recoding data including crack length, time and the like; (2) processing the data to estimate a propagation rate corresponding to the crack length; (3) taking a Paris formula as a least-squares fit line to determine metal material parameters; (4) establishing a crack propagation perturbation series model to obtain a control equation and a boundary condition; (5) selecting a perturbation parameter asymptotic expansion control equation to form a perturbation parameter asymptotic sequence; (6) combining like terms to obtain differential equations under different powers to determine a coefficient to be determined, and carrying out iterative solving on the differential equations to obtain boundary conditions during next calculation; and (7) utilizing a calculation result to finish crack propagation rate estimation, judging whether the crack length exceeds a critical crack or not, jumping to (5) if the crack length exceeds the critical crack, and finishing fatigue life prediction if the crack length exceeds the critical crack. The method can effectively estimate the crack propagation rate and predict the fatigue life, and improves calculation precision.

The invention relates to a creep deformation-fatigue crack growth testing device and a corresponding testing method. The device comprises a loading system, a temperature control system and a measurement and collection system, wherein the measurement and collection system comprises a load linear displacement measurement system and a crack length measurement system; the upper and lower ends of a test sample are fixedly connected with an upper clamp and a lower clamp respectively; a high temperature furnace is connected with the temperature control system and the measurement and collection system; the test sample is loaded by an alternating current servo motor and a controller. The invention further relates to the corresponding testing method. The testing device provided by the invention is compact in structure and convenient to operate; the testing device adopts an insulating chuck and the insulating chuck ensures that constant-current current passing through the test sample is stable; aiming at the test sample of a creep deformation-fatigue crack growth test, the clamps are designed and machined; the temperature in the furnace is high so that a high-temperature clamping type extensometer is used for introducing load linear displacement out of a heating furnace to be measured. The testing method is simple and convenient to operate; the crack length is measured by using an electric potential method and the continuous test can be carried out for long time.

The invention discloses a fatigue life prediction method for a friction stir welded component based on small crack propagation, and belongs to the technical field of fatigue diagnosis and analysis ofmechanical structures. The method comprises the steps that a bone-shaped flat plate sample is prepared, fatigue small crack propagation replica tests under different stress loads and different stressratios are conducted on different areas of a joint, and a secant method is adopted for calculating the propagation rate of small cracks; a New-Raju model is adopted for calculating the stress intensity factor range of the small cracks of the joint; c values in the depth direction and a/2 values in the vertical direction of semi-arc shapes of fatigue crack propagation zones in fracture shapes of different areas of the joint, and the depth-to-length ratio 2c/a of the cracks is calculated; a curve of the propagation rate of the cracks along with the change of the stress intensity factor range isdrawn; an effective stress intensity factor is calculated; a formula of the propagation rate of the small cracks is determined; an initial crack size a0 and a critical crack size ac are determined; the formula of the propagation rate of the small cracks is integrated to obtain the fatigue life of the welded component. By means of the scheme, the fatigue life of the friction stir welded component can be more easily and accurately predicted.

The invention relates to a method for analyzing the residual life of a storage tank through ANSYS software. The method mainly comprises the following steps that (1) a computer supporting ANSYS is used, collected storage tank data are input to the computer in the form of a database or a text, a finite element model of the corroded storage tank is established through the ANSYS software, and corresponding boundary conditions and an external load are applied to the finite element model according to the actual stress condition of the storage tank; (2) regression processing is conducted on experimental data points through a fatigue crack propagation law Paris formula, and a corrosion fatigue rate equation under the corresponding conditions is obtained; (3) the critical invalid wall thickness when the storage tank loses efficacy is determined according to a predicted value of the corrosion rate; (4) according to the critical invalid wall thickness when the storage tank loses efficacy due to corrosion, a storage tank residual life prediction model is established, and the approximate analysis method is used for calculating the residual life of the storage tank under the condition of uniform corrosion.

The invention relates to a method for predicting the high-low-cycle composite fatigue crack growth life of a turbine joggle structure, and the method comprises the steps: (1), building a crack growth model giving consideration to a crack closure effect; (2), determining a high-cycle load stress intensity factor model; (3), determining a low-cycle load stress intensity factor model; (4), judging whether a current cycle is a high-cycle load or not: executing step (5) if the current cycle is the high-cycle load, or else executing step (6); (5), calculating a composite fatigue lower crack increment, judging whether a next cycle is a low-cycle fatigue load or not: obtaining the maximum crack tip opening displacement of the current cycle if the next cycle is the low-cycle fatigue load, and executing step (7), or else executing step (8); (6), calculating the variance of the low-cycle load lower crack tip opening displacement; (7), calculating the residual crack tip opening displacement and crack increment according to the results inputted at steps (5) and (6); (8), updating the crack length, repeatedly carrying out the steps (4)-(7) if the maximum stress intensity factor is less than the fracture toughness, or else completing the calculation, and obtaining the crack growth life.

The invention relates to a test analysis method for lug connecting piece fatigue crack expanding, which is technically characterized by installing a test lug on a testing machine; then loading and producing fatigue crack on the lug; adopting a stress intensity factor comprising a straight lug pulled and loaded lengthwise, the straight lug loaded obliquely smaller than 45 degrees, a symmetrical oblique lug pulled and loaded lengthwise, the symmetrical oblique lug loaded obliquely smaller than 45 degrees, an asymmetrical oblique lug pulled and loaded lengthwise and the asymmetrical oblique lug loaded obliquely smaller than 45 degrees to the corresponding delta K; taking a slope factor of 1g(da / dN)-1g(delta K) line as a constant n in the Paris formula, an intercept of a straight line and axis y as a constant C in the Paris formula, and obtaining the Paris formula when the stress ratio is R; and the lug fatigue crack expanding life NC is estimated according to the obtained Paris formula. The invention has the advantages that the applicability is wide, and the test analytical method plays a directive role in researching the lug hole edge fatigue crack expanding properties under various pulling and loading conditions.

The invention relates to a novel mechanical structure design scheme, which is used for testing test pieces made of various metal and alloy materials at room temperature and bearing tension fatigue characteristic, fatigue life and fatigue crack expansion test of mechanical parts (such as various mechanical connecting pieces). According to the scheme, a motor drives a speed reducer to rotate, the spring is subjected to energy storage by an eccentric shaft coupler and a crank connecting rod mechanism, the spring is controlled by four guide wheels to do vertical reciprocating motion, the potential energy of the spring is converted into moment through a lever, and extension and compression of the spring are reinforced by a lever mechanism, so that tension bars are separated vertically and the stretching effect is achieved; and force amplitude is changed through connecting points at different positions of the lever, so that fatigue tension tests of different frequency and different amplitude are realized. The invention is simple in structure and low in manufacturing cost, adopts a mechanical structure, can meet the basic performance requirement of the fatigue tension test, and can be applied to the tensile fatigue test under the lab environment.

The invention discloses a fatigue crack propagation rate testing method of a steel box girder. The fatigue crack propagation rate obtained by structure solid tests of the method is truer and more reliable than that obtained by the Paris equation obtained by present material tests for fatigue crack propagation. The Paris equation of the method is more instructive when being used for predicating residual life in a service period of a structure. When being used for measuring crack lengths, the method is different from conventional methods that shut down and measure with a vernier caliper. According to the method, a COD clip gauge is mounted to the front end of a mechanical gap of a steel box girder test piece, the linear relation between the COD clip gauge and the crack length a measured by the vernier caliper is calibrated through static load tests, the linear relation is applied to dynamic tests for the fatigue crack propagation rate and the real crack length a is measured directly through reading of the COD clip gauge, and therefore influences on accuracy of fatigue test results, which are caused by crack-tip plastic blunting caused by middle shutdown in dynamic fatigue tests, are avoided, time of shutting down tests and testing crack lengths is saved, and the test efficiency is increased.

A system for testing fatigue crack propagation in a corrosion environment comprises a fatigue testing machine, a medium box, a solution circulating pump, a filter, a flow control valve, a solution tank, a clamp, a crack observing system and a test sample, wherein the test sample is mounted on the clamp, the clamp is connected with the fatigue testing machine, the medium box is arranged on the test sample in a sleeving manner, so that the liquid level of the solution is higher than the to-be-observed part of the test sample, the solution circulating pump conveys an etchant solution filtered by the filter to the medium box from the solution tank, the solution in the medium flows back to the solution tank after the flow speed of the solution is controlled by the flow control valve, and the crack observing system with a microscope records the crack propagation condition through a computer. The system for testing the fatigue crack propagation in the corrosion environment is scientific in conception, simple in structure and convenient in operation and can be used to test the fatigue crack propagation property in the corrosion environment, and the test result has a great important engineering application value for assessing the damage tolerance of a material and a structure in the corrosion environment.

The invention discloses a method for characterizing a steel fatigue crack propagation behavior for casing drilling. The method comprises the steps of: firstly, sampling casing drilling steel, preparing a sample and cleaning; secondly, carrying out low-frequency noise testing on the sample before fatigue; thirdly, carrying out fatigue testing on the sample; fourthly, carrying out low-frequency noise testing on the sample after fatigue; and fifthly, analyzing, extracting and processing low-frequency noise data before and after the fatigue testing according to low-frequency l/f noise information before and after the fatigue, and characterizing a fatigue crack propagation behavior of the sample. Through two times of low-frequency l/f noise testing before and after the fatigue propagation, the influence of background noise of the sample is eliminated, more complex formula derivation and mathematical calculation in common characterizing methods are avoided, no strict requirements are required for the shape of the sample, the fatigue testing quantity is favorably reduced, the testing cost is lowered, and the fatigue crack propagation behaviors of various samples can be conveniently subjected to sampling and fatigue service life estimation; and the method has the characteristics of convenience in use, low cost and convenience in popularization.

The invention relates to a testing system for a fatigue crack propagation test under a high/low temperature environment. The system comprises a fatigue tester, a conversion joint, a sample fixture, a high/low temperature environmental box, a liquid nitrogen tank, positioning pins, a crack observation system and a sample, wherein the sample fixture is mounted on the fatigue tester through the conversion joint; the sample is connected with the sample fixture and is positioned through the positioning pins passing through the positioning holes of the sample fixture and the sample; the sample fixture and the sample are wrapped in the high/low temperature environmental box; the liquid nitrogen tank and the high/low temperature environmental box are communicated so as to realize the low-temperature environment; the crack observation system is used for recording the propagation of cracks by a computer through a microscope; the fatigue tester, the conversion joint, the sample fixture, the positioning pins and the sample are connected in series. The system provided by the invention is simple in structure and convenient to operate, and is used for testing the fatigue crack propagation property test under the high/low temperature environment. A testing result has an important engineering application value for the tolerance evaluation of structural damages.