7 results about "Constant stress" patented technology

The invention belongs to the technical field of aircraft fatigue life design, and particularly relates to an equal stress amplitude vibration fatigue S-N curve determination method and device. The method comprises the following steps: carrying out random vibration response analysis on a structural dynamic finite element model of a cantilever beam with one end clamped and supported, and obtaining a vibration stress power spectral density function and a vibration stress root-mean-square; determining a k-order moment of the vibration stress power spectrum density function; determining a coefficient value of a vibration stress amplitude probability density function formula according to the k-order moment; determining a constant C of the equal stress amplitude vibration fatigue S-N curve; determining a stress amplitude S corresponding to the specified cycle index N according to the constant C; and determining a vibration fatigue SRMS-N curve parallel to the random stress amplitude and a curve passing through the corresponding coordinate points of the cycle index N and the stress amplitude S as an equal stress amplitude vibration fatigue S-N curve. The equal stress amplitude vibration fatigue S-N curve constructed by the invention improves the efficiency of evaluating the vibration fatigue life of the structure.

This invention relates to the field of fatigue performance enhancement technology for metallic materials, and more particularly to a method for improving the fatigue performance of notched components in high-temperature metallic structural materials. Addressing the problem of fatigue failure in notched components of high-temperature metallic structural materials under alternating loads, this invention proposes a method to improve their fatigue performance through pre-creep treatment. This invention applies a controlled constant load or constant stress to the notched component at high temperature and maintains it for a certain period, causing controllable creep at the notch root. This achieves stress relaxation and redistribution, forming a favorable residual stress state and / or microstructure, weakening the notch effect and improving fatigue life. This method has good versatility and can be applied to different types of metallic structural materials, especially suitable for high-temperature fatigue-related components under complex service environments.

The invention discloses a fatigue loading frequency sensitivity testing method for a bimetal composite pipe welded joint in a corrosion environment, and relates to the field of fatigue performance testing of the welded joint in the corrosion environment. The method comprises the following steps: preparing a bimetal composite pipe welding joint CT sample and prefabricating a fatigue crack; coating the non-notched surface of the sample with an anti-corrosion coating, and immersing the sample into a corrosion solution which is subjected to oxygen removal and is introduced with test gas for pre-soaking; a fatigue crack growth rate test is carried out in a corrosion environment and a constant stress intensity factor K control mode, and the loading frequency is gradually reduced along with crack growth; processing the crack propagation data under each frequency, and calculating da / dN of the crack in a stable propagation stage; d / d < N > under different frequencies are compared, when the variation amplitude of adjacent frequencies is smaller than a preset threshold value, it is judged that an environment-insensitive platform area is reached, and the larger value is the optimal loading frequency. According to the method, through step-by-step frequency reduction loading of a single sample, the test cost is remarkably reduced and the test period is remarkably shortened while the accuracy of a test result is ensured.

The invention provides a device and a method for testing a long-time mechanical property degradation process under a dry-wet cycle. The device comprises a triaxial pressure chamber, a loading system, a gas-liquid reactor, an inlet dew point sensor, an outlet dew point sensor, a vacuum pump and a tail liquid pump. The gas-liquid reactor is used for preparing gas-liquid mixtures with different humidity by adjusting the temperature and the gas-liquid ratio and conveying the gas-liquid mixtures to the triaxial pressure chamber; the double-path dew-point sensor is used for monitoring the humidity of a sample inlet and a sample outlet in real time so as to judge the internal humidity balance. During testing, the system is firstly vacuumized, sample humidity balance pretreatment is performed, and then a graded loading creep test under constant humidity is selected, or a dry-wet cycle creep test is performed by regulating and controlling a gas-liquid reactor under constant stress. According to the device and the method, synchronous coupling of stress loading and an accurate and controllable dry-wet cycle environment is realized, the dynamic degradation rule of mechanical parameters of a geotechnical material under the combined action of long-term loading and dry-wet alternation can be accurately revealed, and an effective test and analysis means is provided for long-term stability evaluation of geotechnical engineering.

The utility model relates to a fiber and composite material creep deformation and stress relaxation experiment device which comprises a machine frame, a fixed pulley block is arranged on the machine frame, a traction rope is wound on the fixed pulley block, and a balance module is connected to the traction end, located on one side of the fixed pulley block, of the traction rope. The traction end, located on the other side of the fixed pulley block, of the traction rope is connected with a load module, a force measuring module is connected between the load module and the rack, and a distance measuring module downwards aligned with the load module is arranged beside the force measuring module. The experimental device has the advantages of high measurement precision, visualization, convenience in operation and the like, can be used for testing creep strain evolution and recovery behaviors of fibers or composite materials under the action of constant stress and stress relaxation behaviors of the fibers or the composite materials under constant strain, can also realize synchronous measurement of the stress relaxation behaviors of the materials after creep, and has a wide application prospect. The problem that material viscoelastic creep and stress relaxation experimental devices are incompatible is solved.

The invention discloses a material life loss test method under small-amplitude cyclic load. The method comprises the following steps: preparing a plurality of groups of test samples; keeping the temperature of the test sample within the test temperature range; respectively applying constant stresses with different numerical values to the plurality of groups of test samples to carry out a creep test to obtain fracture stresses of the test samples; taking the fracture stress as high stress, and obtaining low stress according to the high stress; applying a high stress and low stress alternating cycle to the test sample to form a load spectrum of a fatigue waveform, and carrying out a fatigue test; a plurality of creep-fatigue waveform load spectrums are respectively applied to the plurality of groups of test samples to carry out a creep-fatigue alternating test, high stress is changed into low stress, or low stress is changed into high stress to form a diagonal waveform load spectrum; in a high-stress state and / or a low-stress state, corresponding load holding duration is maintained to form a load spectrum of a horizontal line waveform, and the creep-fatigue waveform is a mixed waveform of circulation of an oblique line waveform and the horizontal line waveform.

The invention discloses a method for evaluating the period failure risk and the service life of a high-temperature alloy part by using HEXRD, which comprises the following steps: (1) setting a creep experiment in a synchrotron radiation device, applying constant stress and constant temperature to a high-temperature alloy part sample, starting HEXRD real-time monitoring at the same time, and collecting two-dimensional diffraction ring data at a preset sampling interval; and (2) software is used for processing data, the two-dimensional diffraction ring data is converted into a lattice strain and FWHM evolution curve along with time, peak splitting fitting is conducted on mixed peaks, a fitting result is obtained, and the high-temperature alloy can be Ni-based high-temperature alloy. According to the method, real-time and quantitative monitoring of the initial creep internal stress of the high-temperature alloy is achieved through the in-situ synchrotron radiation technology, the bottleneck that internal stress evolution cannot be dynamically tracked through a traditional method is solved, and direct technical support is provided for service safety evaluation.