scholarly journals Experimental Study on the Creep Behavior of Red Sandstone under Low Temperatures

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Yongjun Song ◽  
Leitao Zhang ◽  
Huimin Yang ◽  
Jianxi Ren ◽  
Yongxin Che
Keyword(s):  
Mechanical Properties ◽  
Low Temperature ◽  
Deformation Characteristics ◽  
Red Sandstone ◽  
Rock Samples ◽  
Uniaxial Creep ◽  
Deformation Properties ◽  
Accelerated Creep ◽  
Different Temperatures

In cold regions, the deformation characteristics and long-term mechanical properties of rocks under low-temperature conditions are considerably different from those in other regions. To study the deformation characteristics and long-term mechanical properties of rocks in a low-temperature environment and the effect of different temperatures, we perform a multilevel loading-unloading uniaxial creep test on red sandstone samples and obtain the creep curves at different temperatures (20°C, −10°C, and −20°C). The results demonstrate that the total strain at each temperature can be divided into instantaneous and creep strains; the instantaneous strain includes instantaneous elastic and plastic strains, and the creep strain includes viscoelastic and viscoplastic strains. Temperature has a significant effect on the deformation properties of red sandstone. A decrease in temperature reduces the instantaneous and creep deformations of the rocks at all levels of stress. In addition, a decrease in temperature exponentially attenuates the total creep and viscoplastic strains of the rocks. 0°C is a critical point for the reduction of the total creep and viscoplastic strains of the rocks. When the temperature is greater than 0°C, the total creep and viscoplastic strains of the rocks decrease rapidly and linearly with decrease in temperature; however, when the temperature is less than 0°C, the decrease in the total creep and viscoplastic strains of the rocks is slow. The steady-state creep rate of the rock samples decreases with decrease in temperature, whereas the creep duration increases with decrease in temperature, especially in the case of the accelerated creep stage. The accelerated creep durations of the rock samples S4 (20°C) and S7 (–10°C) are 0.07 h and 0.23 h, respectively.

Effect of porewater pressure on the mechanical properties of red sandstone with different unloading rates

2020 ◽  
pp. qjegh2019-101
Author(s):  
Jian-Xi Ren ◽  
Xu Chen ◽  
Xing-Zhou Chen ◽  
Meng-Chen Yun ◽  
Xi-TaiLang Cao ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Shear Failure ◽  
Strain Curve ◽  
Shaanxi Province ◽  
Axial Deformation ◽  
Aquifer System ◽  
Red Sandstone ◽  
Rock Samples ◽  
Unloading Rate ◽  
Porewater Pressure

The red sandstone in the Luohe Formation in Shaanxi Province, China, contains a rich aquifer system. The excavation of coal mines and tunnels through the Luohe Formation affects the mechanical properties of the rocks in the surrounding environment, creating the need to determine the effect of the porewater pressure and unloading rate on the mechanical properties of the red sandstone. Using the constant axial pressure unloading method, triaxial unloading tests were performed under different unloading rates (0.1, 0.3 and 0.6 MPa s−1 and porewater pressure conditions (0, 1.0, 1.5 and 2.0 MPa). Based on the results, an unloading statistical damage model of red sandstone was established under the impacts of unloading rate and porewater pressure. During the loading stage, as the porewater pressure increased, the slope of the stress–strain curve and elastic modulus gradually decreased. During the unloading stage, lateral deformation larger than the axial deformation was observed owing to the influence of porewater pressure. The porewater pressure effect became significant as the unloading rate decreased. An increase in porewater pressure or a decrease in the unloading rate increased the confining strain flexibility. Unloading failure of rock samples was dominated by tensile shear failure, thus indicating that a faster unloading rate or larger porewater pressure causes more tensile cracks and severe fracture in the rock samples.

Flip-Chip Ball Grid Array Lead-Free Solder Joint Under Reliability Test

2005 ◽  
Vol 127 (4) ◽  
pp. 446-451 ◽  
Author(s):  
Ming-Hwa R. Jen ◽  
Lee-Cheng Liu ◽  
Jenq-Dah Wu
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Service Time ◽  
Flip Chip ◽  
Failure Modes ◽  
Mechanical Responses ◽  
Operational Life ◽  
Different Temperatures ◽  
Free Solder

The work is aimed to investigate the mechanical responses of bare dies of the combination of pure tin∕Al–NiV–Cu Under bump metallization (UBM) and packages of pure tin∕Al–NiV–Cu UBM/substrate of standard thickness of aurum. The mechanical properties under multiple reflow and long term high temperature storage test (HTST) tests at different temperatures and the operational life were obtained. A scanning electron microscope was used to observe the growth of IMC and the failure modes in order to realize their reaction and connection. From the empirical results of bare dies, the delamination between IMC and die was observed due to the tests at 260 °C multiple reflow. However, their mechanical properties were not affected. Nevertheless, the bump shear strength of bare dies were decreased by HTST tests. In package, all the results of mechanical properties by multiple reflow test and HTST test were significantly lowered. It was shown that the adhesion between bump and die reduced obviously as tests going on. As for high temperature operational life test in the conditions of 150 °C and 320 mA (5040A∕cm2), the average stable service time of the package was 892 h, and the average ultimate service time of the package was 1053 h.

The Effects of Austempering Temperature and Time on Mechanical Properties of Ductile Cast Iron Grade FCD450

2020 ◽  
Vol 856 ◽  
pp. 92-98
Author(s):  
Janthira Chantarach ◽  
Rungsinee Canyook
Keyword(s):  
Mechanical Properties ◽  
Cast Iron ◽  
Low Temperature ◽  
Impact Toughness ◽  
Ductile Cast Iron ◽  
X Ray Diffraction ◽  
X Ray ◽  
Different Temperatures ◽  
Austempering Temperature ◽  
Iron Grade

The purpose of the study was to inspect microstructure, mechanical properties and impact toughness of ductile cast iron grade FCD450 produced by austempering process. The study focused on austempering parameter, which effected impact toughness of material at low temperature. The FCD450 was initially temperature austenized at 885°C (1625˚F) for 2 hours. Austempering was carried out at three different temperatures of 271°C (520˚F), 313°C (560˚F) and 357°C (675˚F). The austempering temperature were varied at 1.5, 2.5 and 3.5 hours. X-ray diffraction was showed that the austempered ductile cast iron (ADI) microstructure consists of austenite and ferrite. The results showed that when austempered at 357°C (675˚F) for 2.5 hours has highest hardness and impact energy at low temperature. The dimple ductile fracture of ADI fracture surfaces was revealed by scanning electron microscope (SEM).

scholarly journals Study on High-Temperature Mechanical Properties of Fe–Mn–C–Al TWIP/TRIP Steel

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 821
Author(s):  
Guangkai Yang ◽  
Changling Zhuang ◽  
Changrong Li ◽  
Fangjie Lan ◽  
Hanjie Yao
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Low Temperature ◽  
Tensile Fracture ◽  
Temperature Range ◽  
High Temperature Mechanical Properties ◽  
Ductility Trough ◽  
Different Temperatures ◽  
Reduction Of Area ◽  
High Temperature Tensile

In this study, high-temperature tensile tests were carried out on a Gleeble-3500 thermal simulator under a strain rate of ε = 1 × 10−3 s−1 in the temperature range of 600–1310 °C. The hot deformation process of Fe–15.3Mn–0.58C–2.3Al TWIP/TRIP at different temperatures was studied. In the whole tested temperature range, the reduction of area ranged from 47.3 to 89.4% and reached the maximum value of 89.4% at 1275 °C. Assuming that 60% reduction of area is relative ductility trough, the high-temperature ductility trough was from 1275 °C to the melting point temperature, the medium-temperature ductility trough was 1000–1250 °C, and the low-temperature ductility trough was around 600 °C. The phase transformation process of the steel was analyzed by Thermo-Calc thermodynamics software. It was found that ferrite transformation occurred at 646 °C, and the austenite was softened by a small amount of ferrite, resulting in the reduction of thermoplastic and formation of the low-temperature ductility trough. However, the small difference in thermoplasticity in the low-temperature ductility trough was attributed to the small amount of ferrite and the low transformation temperature of ferrite. The tensile fracture at different temperatures was characterized by means of optical microscopy and scanning electron microscopy. It was found that there were Al2O3, AlN, MnO, and MnS(Se) impurities in the fracture. The abnormal points of thermoplasticity showed that the inclusions had a significant effect on the high-temperature mechanical properties. The results of EBSD local orientation difference analysis showed that the temperature range with good plasticity was around 1275 °C. Under large deformation extent, the phase difference in the internal position of the grain was larger than that in the grain boundary. The defect density in the grain was large, and the high dislocation density was the main deformation mechanism in the high-temperature tensile process.

Rapid Lifetime Evaluation of Hybrid Composite Rods by Creep Behavior

2013 ◽  
Vol 873 ◽  
pp. 373-378
Author(s):  
Feng Tao Lan ◽  
Ye Wen Cao ◽  
Ying Nan Wang ◽  
Xin Chen ◽  
Chong Zhang
Keyword(s):  
Hybrid Composite ◽  
Superposition Principle ◽  
Mechanical Analysis ◽  
Widespread Application ◽  
Accelerated Creep ◽  
Different Temperatures ◽  
Time Temperature Superposition Principle ◽  
Term Creep ◽  
Short Term Creep

Hybrid composite rods, comprised of unidirectional reinforcing carbon/glass-fiber and adhesive epoxy matrix, are viewed as promising candidates to be used in high-voltage overhead conductors. However, before widespread application, their long-term durability needs to be clarified. In this study, accelerated creep testing for hybrid composite rods, is presented by taking dynamic mechanical analysis tests at different temperatures. Using the time-temperature superposition principle and thermal activation energy theory, the short-term creep data are combined to generate creep long-term compliance master curves. Through the master curve, predictions can be made concerning the creep levels that will occur during the design lifetime of hybrid composite rods (i.e., 30 years). It is found that after 30-year service at 120 °C, fully-cured hybrid composite rods only exhibit a slight increase in compliance (about 5%), indicating a satisfactory creep resistance at this temperature.

Microstuctural and Mechanical Properties of Zirconia-Silica-Hydroxyapatite Composite for Biomedical Applications

2014 ◽  
Vol 631 ◽  
pp. 156-159
Author(s):  
Aliye Arabaci ◽  
Nazlican Yüksel ◽  
Nermin Demirkol
Keyword(s):  
Mechanical Properties ◽  
Composite Material ◽  
Biomedical Applications ◽  
Sintering Behavior ◽  
Microstructural Characteristics ◽  
Calcium Phosphate Ceramic ◽  
Hydroxyapatite Composite ◽  
Different Temperatures ◽  
Zirconia Powders

Hydroxyapatite is a calcium phosphate ceramic that is used as a biomaterial. It has been studied extensively as a candidate biomaterial for prosthetic applications. Hydroxyapatite (HA) does not have the mechanical strength to enable it to succeed in long term load bearing applications. Therefore, Its mechanical properties may be improved with addition of zirconia powders. The aim of this study is to improve the mechanical properties of the hydroxyapatite by producing composite material including zirconia and silica powders. Therefore, hydroxyapatite was mixed with 5 wt% zirconia, 5 wt% silica powders and then this pressed mixture were sintered at different temperatures (1100-1300°C). The sintering behavior, microstructural characteristics and mechanical properties were investigated.

scholarly journals Experimental Study on Mechanical Properties of Prefabricated Single-Cracked Red Sandstone under Uniaxial Compression

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Yue Yuan ◽  
Jinlei Fu ◽  
Xiaolei Wang ◽  
Xi Shang
Keyword(s):  
Mechanical Properties ◽  
Crack Propagation ◽  
Failure Mode ◽  
Uniaxial Compression ◽  
Contact Force ◽  
Rock Sample ◽  
Unstable Fracture ◽  
Red Sandstone ◽  
Rock Samples ◽  
Dip Angle

This paper aims at the phenomenon of the fractured rock column in underground engineering which is prone to collapse when subjected to ground pressure. Uniaxial compression test and particle flow code (PFC2D) are used to analyze the influence of crack dip angle on the mechanical properties, crack propagation, and the failure mode of red sandstone. From the results, it is observed that the stress–strain curve of the precracked red sandstone can be divided into five stages, and there is a critical stress value in the stage of accelerated crack propagation and unstable fracture of the rock sample. Further, the peak strength, maximum strain, and the elastic modulus of the precracked red sandstone increase with the increase of crack dip angle, and the ultimate failure mode of rock sample changes from the “ladder” type failure to slope uneven failure. Furthermore, from PFC2D simulation, it is found that the tensile microcracks contribute more towards the failure of rock samples than the shear cracks. The contact force chain is very weak at the places where the precracks and macroshear planes are formed. This indicates that the original contact force is weakened due to particle fracture. Therefore, the bearing capacity of the precracked rock samples decreases with the increase in load. From the simulation results, it is found that the displacement at the shear plane of the rock sample is large, and the shear dilatation occurs. With the increase in load, the specimen falls off and is ejected. This is due to the weakening of the contact force between the internal particles. Thereafter, it fractures to produce microcracks, which gradually converge, thus providing a prerequisite for the transformation of elastic strain energy into kinetic energy.

The Rehbinder effect in tests of superalloys in contact with molten salts

2021 ◽  
Vol 87 (10) ◽  
pp. 54-62
Author(s):  
L. B. Getsov ◽  
M. Yu. Balandina ◽  
A. I. Grishchenko ◽  
A. B. Laptev ◽  
A. I. Puzanov
Keyword(s):  
Mechanical Properties ◽  
Single Crystal ◽  
Molten Salts ◽  
Term Strength ◽  
Initial State ◽  
Rehbinder Effect ◽  
Corrosive Media ◽  
Term Operation ◽  
Different Temperatures

The results of the Rehbinder effect manifestation during testing of superalloys in contact with corrosive media containing Na2SO4 + NaCl are discussed. We present the experimental study of the effect of salts containing chlorine and sulfur on the mechanical properties and long-term strength of single crystal and powder nickel-based superalloys at high temperatures. The practical value of the work is associated with the possible operation of gas turbine parts in conditions of ingress of the particles containing chlorine, sulfur and sodium into the flow path. A simplified (compared to a previously used) procedure of testing wrought alloys for long-term strength in molten salts is developed. A comparative study of the mechanical properties and long-term strength of a single crystal superalloy in the initial state (previously damaged by corrosion of different duration) and being in contact with salts during testing is carried out. Due to the large scatter of experimental data, the method of lower envelopes has been proposed and implemented to determine the guaranteed values of the long-term strength. It is shown that the guaranteed values of the long-term strength at different temperatures and test durations can decrease by 2.5 – 5.0 times in the presence of salts. Metallographic studies of the nature of damage and destruction of samples are carried out. The revealed decrease in the long-term strength of heat-resistant alloys in contact with salts is interpreted as the Rehbinder effect and not as a manifestation of the effect of stress corrosion cracking. A methodology for using the obtained test results with a duration of up to several thousand hours in highly aggressive environments is proposed to predict the long-term strength in relation to long-term operation (tens of thousands of hours) under conditions of relatively low salt loads.

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