Influence of specimen height-to-width ratio on the strainburst characteristics of Tianhu granite under true-triaxial unloading conditions

2015 ◽  
Vol 52 (7) ◽  
pp. 890-902 ◽  
Author(s):  
X.G. Zhao ◽  
M. Cai
Keyword(s):  
High Speed ◽  
Failure Process ◽  
Test System ◽  
Width Ratio ◽  
Underground Structures ◽  
True Triaxial ◽  
Ae Energy ◽  
Specimen Height ◽  
Full Face ◽  
Cumulative Ae Energy

Strainbursts occur frequently near excavation boundaries, posing a significant threat to the safety of workers and stability of underground structures. A better understanding of the strainburst phenomenon is important for safe underground construction and risk management. This paper presents the results of an experimental study on strainburst behaviours of Tianhu granite with four specimen height-to-width (H/W) ratios. A series of tests under unloading conditions were conducted using a true-triaxial strainburst test system that was equipped with an acoustic emission (AE) monitoring system. A high-speed camera was used to capture the instantaneous strainburst process of the specimens on the unloading surface. The experimental results indicate that regardless of the H/W ratio, strainbursts occurred in all specimens but strainburst characteristics depend on the H/W ratio. When the H/W ratio changes from 2.5 to 1.0, the dynamic failure process of the unloading surface transforms from local rock ejection to full-face burst. The strainburst is more violent when the H/W ratio is small. Analysis of the cumulative AE energy revealed that the cumulative AE energy is not sensitive to the H/W ratio for ratios lower than 1.5. When the H/W ratio is greater than 1.5, the cumulative AE energy shows a decreasing trend during rock failure.

scholarly journals Research on Performance Test System of Space Harmonic Reducer in High Vacuum and Low Temperature Environment

Machines ◽  
2020 ◽  
Vol 9 (1) ◽  
pp. 1
Author(s):  
Jing Wang ◽  
Zhihua Wan ◽  
Zhurong Dong ◽  
Zhengguo Li
Keyword(s):  
Low Temperature ◽  
High Speed ◽  
Performance Test ◽  
High Reliability ◽  
High Vacuum ◽  
Test System ◽  
Low Noise ◽  
Speed Ratio ◽  
Space Harmonic ◽  
Temperature Environment

The harmonic reducer, with its advantages of high precision, low noise, light weight, and high speed ratio, has been widely used in aerospace solar wing deployment mechanisms, antenna pointing mechanisms, robot joints, and other precision transmission fields. Accurately predicting the performance of the harmonic reducer under various application conditions is of great significance to the high reliability and long life of the harmonic reducer. In this paper, a set of automatic harmonic reducer performance test systems is designed. By using the CANOpen bus interface to control the servo motor as the drive motor, through accurately controlling the motor speed and rotation angle, collecting the angle, torque, and current in real time, the life cycle test of space harmonic reducer was carried out in high vacuum and low temperature environment on the ground. Then, the collected data were automatically analyzed and calculated. The test data of the transmission accuracy, backlash, and transmission efficiency of the space harmonic reducer were obtained. It is proven by experiments that the performance data of the harmonic reducer in space work can be more accurately obtained by using the test system mentioned in this paper, which is convenient for further research on related lubricating materials.

Contusion, dislocation, and distraction: primary hemorrhage and membrane permeability in distinct mechanisms of spinal cord injury

2007 ◽  
Vol 6 (3) ◽  
pp. 255-266 ◽  
Author(s):  
Anthony M. Choo ◽  
Jie Liu ◽  
Clarrie K. Lam ◽  
Marcel Dvorak ◽  
Wolfram Tetzlaff ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Spinal Cord Injury ◽  
White Matter ◽  
Animal Models ◽  
Membrane Permeability ◽  
High Speed ◽  
Test System ◽  
Fracture Dislocation ◽  
Sprague Dawley ◽  
Cord Injury

Object In experimental models of spinal cord injury (SCI) researchers have typically focused on contusion and transection injuries. Clinically, however, other injury mechanisms such as fracture–dislocation and distraction also frequently occur. The objective of the present study was to compare the primary damage in three clinically relevant animal models of SCI. Methods Contusion, fracture–dislocation, and flexion–distraction animal models of SCI were developed. To visualize traumatic increases in cellular membrane permeability, fluorescein–dextran was infused into the cerebrospi-nal fluid prior to injury. High-speed injuries (approaching 100 cm/second) were produced in the cervical spine of deeply anesthetized Sprague–Dawley rats (28 SCI and eight sham treated) with a novel multimechanism SCI test system. The animals were killed immediately thereafter so that the authors could characterize the primary injury in the gray and white matter. Sections stained with H & E showed that contusion and dislocation injuries resulted in similar central damage to the gray matter vasculature whereas no overt hemorrhage was detected following distraction. Contusion resulted in membrane disruption of neuronal somata and axons localized within 1 mm of the lesion epicenter. In contrast, membrane compromise in the dislocation and distraction models was observed to extend rostrally up to 5 mm, particularly in the ventral and lateral white matter tracts. Conclusions Given the pivotal nature of hemorrhagic necrosis and plasma membrane compromise in the initiation of downstream SCI pathomechanisms, the aforementioned differences suggest the presence of mechanism-specific injury regions, which may alter future clinical treatment paradigms.

Numerical and experimental studies on the thermal and static characteristics of multi-leaf foil thrust bearing

2021 ◽  
pp. 135065012110110
Author(s):  
Yu Guo ◽  
Yu Hou ◽  
Qi Zhao ◽  
Xionghao Ren ◽  
Shuangtao Chen ◽  
...  
Keyword(s):  
High Speed ◽  
Thrust Bearing ◽  
Load Capacity ◽  
Failure Process ◽  
Experimental Studies ◽  
Elastic Model ◽  
Static Characteristics ◽  
Bearing Load ◽  
Foil Thrust Bearing ◽  
Cooling Air

Foil bearing is considered to be a promising supporting technology in high-speed centrifugal machinery. Due to the high-speed shearing effect in the viscous lubricant film, heat generation could not be ignored. In this paper, a thermo-elastic model of the multi-leaf foil thrust bearing is proposed to predict its thermal and static characteristics. In the model, modified Reynolds equation, energy equation, and Kirchhoff equation are solved in a coupling way. The contact area between the foil and welding plate is taken into account. Besides, the effect of cooling air on the bearing temperature is investigated. The ultimate load capacity and transient overload failure process of the bearing is analyzed and discussed. The effect of rotation speed on the bearing temperature is more obvious than that of the bearing load. The bearing temperature drops obviously by introducing the cooling air, and the cooling effect is improved with the supply pressure. The transient overload failure of the bearing occurs when the bearing load exceeds the ultimate value.

Rotordynamic Performance of a Rotor Supported on Bump Type Foil Gas Bearings: Experiments and Predictions

2006 ◽  
Vol 129 (3) ◽  
pp. 850-857 ◽  
Author(s):  
Luis San Andrés ◽  
Dario Rubio ◽  
Tae Ho Kim
Keyword(s):  
High Speed ◽  
Critical Speed ◽  
Load Capacity ◽  
Test System ◽  
Foil Bearings ◽  
Rotor Imbalance ◽  
Synchronous Motion ◽  
Damping Characteristics ◽  
Rotor Surface ◽  
Stiffness And Damping

Gas foil bearings (GFBs) satisfy the requirements for oil-free turbomachinery, i.e., simple construction and ensuring low drag friction and reliable high speed operation. However, GFBs have a limited load capacity and minimal damping, as well as frequency and amplitude dependent stiffness and damping characteristics. This paper provides experimental results of the rotordynamic performance of a small rotor supported on two bump-type GFBs of length and diameter equal to 38.10mm. Coast down rotor responses from 25krpm to rest are recorded for various imbalance conditions and increasing air feed pressures. The peak amplitudes of rotor synchronous motion at the system critical speed are not proportional to the imbalance introduced. Furthermore, for the largest imbalance, the test system shows subsynchronous motions from 20.5krpm to 15krpm with a whirl frequency at ∼50% of shaft speed. Rotor imbalance exacerbates the severity of subsynchronous motions, thus denoting a forced nonlinearity in the GFBs. The rotor dynamic analysis with calculated GFB force coefficients predicts a critical speed at 8.5krpm, as in the experiments; and importantly enough, unstable operation in the same speed range as the test results for the largest imbalance. Predicted imbalance responses do not agree with the rotor measurements while crossing the critical speed, except for the lowest imbalance case. Gas pressurization through the bearings’ side ameliorates rotor subsynchronous motions and reduces the peak amplitudes at the critical speed. Posttest inspection reveal wear spots on the top foils and rotor surface.

Design of an Intelligent Multi-Gyro Measurement Device

2005 ◽  
Vol 295-296 ◽  
pp. 589-594
Author(s):  
J.P. Wang ◽  
W. Zhou ◽  
W.F. Tian ◽  
Z.H. Jin
Keyword(s):  
High Speed ◽  
Dynamic Balance ◽  
Control Unit ◽  
Calibration Method ◽  
Test System ◽  
Measurement Device ◽  
Logic Control ◽  
Hardware Description ◽  
Thermal Resistors ◽  
Inertial Unit

This paper describes the design of an intelligent multi-gyro measurement device to measure and monitor an inertial unit composed of three dynamically tuned gyros (DTGs). A 16-bit microprogrammed control unit is programmed to fulfill the functions of signal processing, logic control and serial communication with a master computer. An FPGA, designed by using Verilog Hardware Description Language, is used to realize high speed 16-bit reversible counters for output pulses of the DTG digital dynamic balance circuits. The count values represent the angular motion of the inertial unit. A stepping electric bridge is employed to measure the resistance of thermal resistors within the gyros in a wide temperature environment. The resistance represents the working temperature of the gyros. An effective calibration method for the bridge is developed to eliminate the resistance measurement error. A test system is established to examine whether the device meets the user requirements. Results of the tests show that the device has a good performance. A trial use has proved that the device is stable and reliable and that it satisfies the demand of the user.

Failure Process of Rock Sample Observed by AE Source Locating Technique under Uniaxial Compression

2006 ◽  
Vol 324-325 ◽  
pp. 567-570
Author(s):  
Yuan Hui Li ◽  
Rui Fu Yuan ◽  
Xing Dong Zhao
Keyword(s):  
Uniaxial Compression ◽  
High Speed ◽  
Failure Process ◽  
Compression Tests ◽  
Temporal And Spatial Distribution ◽  
Primary Stage ◽  
Brewing Process ◽  
Ae Signal ◽  
Failure Location ◽  
Low Amplitude

A series of uniaxial-compression tests were conducted on some representative brittle rock specimens, such as granite, marble and dolerite. A multi-channel, high-speed AE signal acquiring and analyzing system was employed to acquire and record the characteristics of AE events and demonstrate the temporal and spatial distribution of these events during the rupture-brewing process. The test result showed that in the primary stage, many low amplitude AE events were developed rapidly and distributed randomly throughout the entire specimens. In the second stage, the number of AE increased much slower than that in the first stage, while the amplitude of most AE events became greater. Contrarily to the primary stage, AE events clustered in the middle area of the specimen and distributed vertically conformed to the orientation of compression. The most distinct characteristic of this stage was a vacant gap formed approximately in the central part of the specimen. In the last stage, the number of AE events increased sharply and their magnitude increased accordingly. The final failure location coincidently inhabited the aforementioned gap. The main conclusion is that most macrocracks are developed from the surrounding microcracks existed earlier and their positions occupy the earlier formed gaps, and the AE activity usually becomes quite acute before the main rupture occurs.

Electron-beam test system for high-speed devices

Scanning ◽  
1987 ◽  
Vol 9 (5) ◽  
pp. 201-204 ◽  
Author(s):  
M. Brunner ◽  
D. Winkler ◽  
R. Schmitt ◽  
B. Lischke
Keyword(s):  
Electron Beam ◽  
High Speed ◽  
Test System ◽  
Beam Test

Effects of Geometry, Temperature, and Test Procedure on Reported Failure Strains From Simulated Wide Plate Tests

2006 ◽  
Author(s):  
Yong-Yi Wang ◽  
Ming Liu ◽  
Yaoshan Chen ◽  
David Horsley
Keyword(s):  
Test Data ◽  
Failure Process ◽  
Test Procedure ◽  
Gage Length ◽  
Tensile Failure ◽  
Temperature Fields ◽  
Weld Strength ◽  
Width Ratio ◽  
Local Cooling ◽  
Linear Variable Displacement Transducer

Wide plate test is a valuable tool in the assessment of pipeline girth weld integrity. It has been used for welding procedure qualification and for the validation of theoretically based defect assessment procedures. Although the general form of the test has remained largely unchanged over the years, the size of the test specimen, strain measurement, and test procedure, has had some variations. The influence of these variables has not been adequately examined. While this might be acceptable for tests targeted for stress-based design in which a general pass/no-pass answer is desired, the requirements for data accuracy and consistency for strain-based design are much higher. Understanding the variability of the test data is critical for high strain applications. This paper examines the effects of test geometry, mainly the length to width ratio, on the reported failure strains, assuming material’s failure process remains the same. The influence of different strain measdurement procedures, such as the location and gage length of LVDTs (Linear Variable Displacement Transducer), is assessed for different materials and weld strength mismatch levels. The other consideration is the influence of temperature fields on the cold test data. The postulated cold tests use either local cooling at the location of the weld defect or uniform cooling. In the case of local cooling, the gage length of the LVDTs covers materials of different temperatures. Consequently the reported failure strains are affected by the distribution of the temperature fields. The effects of the temperature fields on the reported tensile failure strains are examined.

Damage Observation and Analysis of a Rock Brazilian Disc Using High-Speed DIC Method

2011 ◽  
Vol 70 ◽  
pp. 87-92 ◽  
Author(s):  
Shao Peng Ma ◽  
Dong Yan ◽  
Xian Wang ◽  
Yan Yan Cao
Keyword(s):  
Strain Field ◽  
Damage Evolution ◽  
High Speed ◽  
Failure Process ◽  
Tensile Load ◽  
Brazilian Test ◽  
Elastic Model ◽  
Strain Fields ◽  
Brazilian Disc ◽  
Damage And Failure

Observation of damage evolution is of great importance to the understanding of the failure process of rock materials. High-speed DIC system is constructed and used to observe the strain field evolution of the granodiorite disc in Brazilian test. The strain fields at different load levels are analyzed based on the stain abnormality indicator (SAI) which is the ratio of the strain measured in experiment to the strain from theoretical solution in an isotropy and elastic model. SAI could be used to indicate the damage in the specimen. The process of damage and failure of the specimen in Brazilian disc test is quantitatively analyzed and deeply discussed according to the strain fields and the statistics of SAI. Experimental results in this paper show that the failure process of the disc specimen in Brazilian test is not simple crack propagation under tensile load, but a complicated damage evolution procedure.

Test System for Mechanical Property of Geotextile Material Based on PCI-1714

2012 ◽  
Vol 455-456 ◽  
pp. 217-221
Author(s):  
Zhi Gang Liu ◽  
Qi Xiao Sun
Keyword(s):  
Mechanical Property ◽  
Data Acquisition ◽  
High Speed ◽  
Test System ◽  
Overall Design ◽  
Data Acquisition Software ◽  
Mechanics Performance ◽  
Data Acquisition Card ◽  
High Speed Data Acquisition ◽  
High Speed Data

A solution of intelligent test system for mechanical property of geotextile material which based on high speed data acquisition card PCI-1714 is introduced in this paper. Microprocessor and drive card PCI-1240 are also used to control and drive the test equipment. The article discussed in detail the system’s overall design, the hardware structure, software design, and process of data acquisition. Software is designed by Visual Basic 6.0. This paper research and implement on accurate measurement of mechanics performance of geotextile material.

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