scholarly journals Mechanical analysis on cement sheath integrity under asymmetric load

2021 ◽  
Author(s):  
Xiaoyu Zhang ◽  
Lei Wang ◽  
Zhenhui Bi ◽  
Yintong Guo ◽  
Chunhe Yang ◽  
...  
Keyword(s):  
High Temperature ◽  
Cyclic Loading ◽  
Stress Distribution ◽  
Negative Impact ◽  
Plastic Material ◽  
Accumulation Rate ◽  
Triaxial Compression ◽  
External Pressure ◽  
Engineering Practice ◽  
Asymmetric Stress

AbstractIn large-scale multi-section hydraulic fracturing, the stress environment of wellbore is extreme complex, often causing the unbalanced stress distribution around the wellbore. That poses great challenges to the integrity of the sheath. In this paper, firstly, triaxial compression test and triaxial cyclic test are carried out at 130 °C to study the deformation characteristics of the cement under high temperature. Then based on that, an appropriate plastic mechanics model is established. Finally, the shakedown theory is applied to analyze the model and acquires a maximum cyclic loading under asymmetric stress. The result shows that (1) the well cement, with the increase of load, shows the plastic flow characteristics and can be regarded as an ideal elastic–plastic material under high temperature. (2) During the cyclic loading and unloading process, the "hysteresis loop" becomes denser, which indicates that the accumulation rate of plastic deformation is continuously declining. The main plastic strain appears in the phase of the first loading. (3) The external pressure Pz plays a positive role in the deformation control of the sheath. With the growth of Pz, the maximum cyclic loading Pmax will also increase. (4) Asymmetric stress distribution can significantly affect the bearing capacity of the sheath. If stress difference coefficient λ = 0.3, the Pmax tends to decrease nearly by 50%. With the growth of λ, the negative influence of stress asymmetry reduces gradually. High external pressure is beneficial to reduce the negative impact of the asymmetry. With the growth of λ, the benefit tends to enhance. (5) In engineering practice, if the geology around wellhole showcases the strong asymmetry (the value of λ is large), some steps need to be adopted to reduce the stress concentration.

scholarly journals Relationship between monotonic and cyclic behavior of saturated soft clay in undrained triaxial compression tests

2021 ◽  
Author(s):  
Tingyu Wu ◽  
Jie Han ◽  
Yuanqiang Cai ◽  
Lin Guo ◽  
Jun Wang
Keyword(s):  
Cyclic Loading ◽  
Triaxial Compression ◽  
Soft Clay ◽  
Cyclic Behavior ◽  
Triaxial Tests ◽  
Engineering Practice ◽  
Compression Tests ◽  
Cyclic Tests ◽  
Saturated Soft Clay ◽  
Triaxial Compression Tests

Cyclic loading-induced deformation of soil is a common problem in the engineering practice. In the current practice, however, monotonic triaxial tests are more commonly used in the practice, due to the availability of apparatus and ease of operation. Thus, it will be very useful and practical if the monotonic triaxial tests can be used to evaluate the behavior of soil under cyclic loading. This study aims to find an explicit relationship between monotonic and cyclic behavior of saturated soft clay. Six monotonic and nine cyclic triaxial compression tests were conducted on undisturbed saturated soft clay under an undrained condition. The test results showed that the monotonic and cyclic tests shared the same stress-strain surface in a three-dimensional space p^'-q-ε_a. It is also found possible to evaluate the effective stress states of cyclic tests at two specific numbers of cycles, using corresponding monotonic tests. Based on these two findings, a simple procedure was then proposed to predict the peak axial strain for the saturated soft clay under different cyclic loadings based on the monotonic tests and only one cyclic test, which was further verified against more test data from the previous literature.

The Issue of Plastic and Microplastic Pollution in Soil

2019 ◽  
Vol 56 (3) ◽  
pp. 484-487 ◽  
Author(s):  
Valentina Constanta Tudor ◽  
Dorina Nicoleta Mocuta ◽  
Ruxandra Florina Teodorescu ◽  
Dragos Ion Smedescu
Keyword(s):  
Water Pollution ◽  
Organic Matter ◽  
Soil Pollution ◽  
Aquatic Environment ◽  
Negative Impact ◽  
Plastic Material ◽  
Soil Biota ◽  
Toxic Substances

Soil pollution with plastics represents a great threat to plants, animals, but especially to humans, as a very small quantity of the plastic which is discarded daily is recycled or incinerated in waste facilities, much of it reaching landfills where their decomposition lasts up to 1000 years and during this time the toxic substances penetrate the soil and the water. If, initially, the pollution with plastics has been identified and recognized in the aquatic environment, recent studies show that plastics residues exist in huge quantities in the soil. The present study focuses on the analysis of factors that pollute soil, so the various studies that have been carried out claim that soil pollution with plastic is much higher and increases in an aggressive manner, being estimated to be 4 to 23 times higher than water pollution with plastics, and the accumulation of microplastics in the soil has a negative impact on soil biota. Thus, once the plastic material accumulates in the soil, it is assimilated to organic matter and the mineral substitutes of the soil and persists for several hundred years.

scholarly journals On the Plastic Strain Accumulation in Notched Bars During High-Temperature Creep Dwell

2020 ◽  
Vol 36 (2) ◽  
pp. 167-176 ◽  
Author(s):  
Daniele Barbera ◽  
Haofeng Chen
Keyword(s):  
High Temperature ◽  
Cyclic Loading ◽  
Plastic Strain ◽  
Kinematic Hardening ◽  
High Temperature Creep ◽  
Strain Accumulation ◽  
Material Models ◽  
Cyclic Loading Condition ◽  
Hardening Material ◽  
Temperature Creep

ABSTRACTStructural integrity plays an important role in any industrial activity, due to its capability of assessing complex systems against sudden and unpredicted failures. The work here presented investigates an unexpected new mechanism occurring in structures subjected to monotonic and cyclic loading at high temperature creep condition. An unexpected accumulation of plastic strain is observed to occur, within the high-temperature creep dwell. This phenomenon has been observed during several full inelastic finite element analyses. In order to understand which parameters make possible such behaviour, an extensive numerical study has been undertaken on two different notched bars. The notched bar has been selected due to its capability of representing a multiaxial stress state, which is a practical situation in real components. Two numerical examples consisting of an axisymmetric v-notch bar and a semi-circular notched bar are considered, in order to investigate different notches severity. Two material models have been considered for the plastic response, which is modelled by both Elastic-Perfectly Plastic and Armstrong-Frederick kinematic hardening material models. The high-temperature creep behaviour is introduced using the time hardening law. To study the problem several results are presented, as the effect of the material model on the plastic strain accumulation, the effect of the notch severity and the mesh element type and sensitivity. All the findings further confirm that the phenomenon observed is not an artefact but a real mechanism, which needs to be considered when assessing off-design condition. Moreover, it might be extremely dangerous if the cyclic loading condition occurs at such a high loading level.

scholarly journals Mechanical Properties of Spruce Wood Extracted from GLT Beams Loaded by Fire

2021 ◽  
Vol 13 (10) ◽  
pp. 5494
Author(s):  
Lucie Kucíková ◽  
Michal Šejnoha ◽  
Tomáš Janda ◽  
Jan Sýkora ◽  
Pavel Padevět ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Cross Section ◽  
Negative Impact ◽  
Tensile Tests ◽  
Thermal Recovery ◽  
Bending Test ◽  
Small Scale ◽  
Spruce Wood ◽  
The Impact

Heating wood to high temperature changes either temporarily or permanently its physical properties. This issue is addressed in the present contribution by examining the effect of high temperature on residual mechanical properties of spruce wood, grounding on the results of full-scale fire tests performed on GLT beams. Given these tests, a computational model was developed to provide through-thickness temperature profiles allowing for the estimation of a charring depth on the one hand and on the other hand assigning a particular temperature to each specimen used subsequently in small-scale tensile tests. The measured Young’s moduli and tensile strengths were accompanied by the results from three-point bending test carried out on two groups of beams exposed to fire of a variable duration and differing in the width of the cross-section, b=100 mm (Group 1) and b=160 mm (Group 2). As expected, increasing the fire duration and reducing the initial beam cross-section reduces the residual bending strength. A negative impact of high temperature on residual strength has also been observed from simple tensile tests, although limited to a very narrow layer adjacent to the charring front not even exceeding a typically adopted value of the zero-strength layer d0=7 mm. On the contrary, the impact on stiffness is relatively mild supporting the thermal recovery property of wood.

A Method for Predicting the Behavior of Plastics at Different Temperatures

2014 ◽  
Vol 1039 ◽  
pp. 107-111
Author(s):  
Yang Chen ◽  
Gui Qin Li ◽  
Bin Ruan ◽  
Xiao Yuan ◽  
Hong Bo Li
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Constitutive Model ◽  
Research And Development ◽  
Mechanical Behavior ◽  
Plastic Material ◽  
Different Temperatures ◽  
Plastic Parts

The mechanical behavior of plastic material is dramatically sensitive to temperature. An method is proposed to predict the mechanical behavior of plastics for cars, ranging from low-temperature low temperature ≤-40°C to high temperature ≥80°C. It dominates the behavior of plastic material based on improved constitutive model in which the parameters adjusted by a series of tests under different temperatures. The method is validated with test and establishes the basis for research and development of plastic parts for automobile as well.

Effect of Damping Constants and Stress Distribution on the Resonance Response of Members

1953 ◽  
Vol 20 (2) ◽  
pp. 201-209
Author(s):  
B. J. Lazan
Keyword(s):  
Stress Distribution ◽  
Amplification Factor ◽  
Engineering Practice ◽  
Distribution Factor ◽  
Mathematical Relationship ◽  
Cross Sectional ◽  
Resonance Response ◽  
Properties Of Materials ◽  
Material Factor ◽  
Sectional Shape

Abstract The amplitude of vibration of a member at resonance, as defined by its resonance amplification factor, is analyzed in relationship to the damping properties of materials. Data are presented on damping energy to indicate the effect of stress magnitude, stress history, and temperature. Based on the mathematical relationship found to exist between damping and stress magnitude the resonance amplification factors are determined for a variety of direct stress members and beams. It is shown that the amplification in vibration caused by resonance may be considered to be the product of three basic factors, i.e., (a) the material factor, (b) the cross-sectional shape factor, and (c) the longitudinal stress-distribution factor. The first of these factors may be calculated from the damping and dynamic modulus properties of the material and the last two from the shape and loading characteristics of the member. Diagrams are presented to show these basic factors as functions of the damping exponent and other variables for members commonly encountered in engineering practice. Experimental data are presented to confirm the equations derived for resonance amplification factor of members having various shapes and stress distribution.

scholarly journals Superalloy Technology - A Perspective on Critical Innovations for Turbine Engines

2008 ◽  
Vol 380 ◽  
pp. 113-134 ◽  
Author(s):  
Robert Schafrik ◽  
Robert Sprague
Keyword(s):  
High Temperature ◽  
Customer Value ◽  
Oil And Gas ◽  
Driving Forces ◽  
Ceramic Materials ◽  
Nickel Superalloy ◽  
Engineering Practice ◽  
Jet Engines ◽  
Societal Benefit ◽  
Development Paradigm

High temperature structural materials, such as nickel-based superalloys, have contributed immensely to societal benefit. These materials provide the backbone for many applications within key industries that include chemical and metallurgical processing, oil and gas extraction and refining, energy generation, and aerospace propulsion. Within this broad application space, the best known challenges tackled by these materials have arisen from the demand for large, efficient land-based power turbines and light-weight, highly durable aeronautical jet engines. So impressive has the success of these materials been that some have described the last half of the 20th century as the Superalloy Age. Many challenges, technical and otherwise, were overcome to achieve successful applications. This paper highlights some of the key developments in nickel superalloy technology, principally from the perspective of aeronautical applications. In the past, it was not unusual for development programs to stretch out 10 to 20 years as the materials technology was developed, followed by the development of engineering practice, and lengthy production scaleup. And many developments fell by the wayside. Today, there continue to be many demands for improved high temperature materials. New classes of materials, such as intermetallics and ceramic materials, are challenging superalloys for key applications, given the conventional wisdom that superalloys are reaching their natural entitlement level. Therefore, multiple driving forces are converging that motivate improvements in the superalloy development process. This paper concludes with a description of a new development paradigm that emphasizes creativity, development speed, and customer value that can provide superalloys that meet new needs.

Identification of Failure Modes Under Design Extension Conditions

2015 ◽  
Author(s):  
Naoto Kasahara ◽  
Izumi Nakamura ◽  
Hideo Machida ◽  
Hitoshi Nakamura ◽  
Koji Okamoto
Keyword(s):  
High Temperature ◽  
Nuclear Power ◽  
Failure Modes ◽  
Low Cycle Fatigue ◽  
External Pressure ◽  
Lessons Learned ◽  
Local Failure ◽  
Severe Accident ◽  
Mitigation Measures ◽  
Loading Mode

As the important lessons learned from the Fukushima-nuclear power plant accident, mitigation of failure consequences and prevention of catastrophic failure became essential against severe accident and excessive earthquake conditions. To improve mitigation measures and accident management, clarification of failure behaviors with locations is premise under design extension conditions such as severe accidents and earthquakes. Design extension conditions induce some different failure modes from design conditions. Furthermore, best estimation for these failure modes are required for preparing countermeasures and management. Therefore, this study focused on identification of failure modes under design extension conditions. To observe ultimate failure behaviors of structures under extreme loadings, new experimental techniques were adopted with simulation materials such as lead and lead-antimony alloy, which has very small yield stress. Postulated failure modes of main components under design extension conditions were investigated according three categories of loading modes. The first loading mode is high temperature and internal pressure. Under this mode, ductile fracture and local failure were investigated. At the structural discontinuities, local failure may become dominant. The second is high temperature and external pressure loading mode. Buckling and fracture were investigated. Buckling occurs however hardly break without additional loads or constraints. The last loading is excessive earthquake. Ratchet deformation, collapse, and fatigue were investigated. Among them, low-cycle fatigue is dominant.

scholarly journals Bond Fatigue of TRC with Epoxy Impregnated Carbon Textiles

2019 ◽  
Vol 9 (10) ◽  
pp. 1980 ◽  
Author(s):  
Juliane Wagner ◽  
Manfred Curbach
Keyword(s):  
Cyclic Loading ◽  
Residual Strength ◽  
Negative Impact ◽  
Fatigue Behavior ◽  
Tensile Load ◽  
Textile Reinforced Concrete ◽  
Anchorage Length ◽  
Static Tests ◽  
Number Of Cycles ◽  
Bearing Behavior

For the economical construction of fatigue loaded structures with textile reinforced concrete (TRC), it is necessary to investigate the fatigue behavior of the materials. Since next to the tensile load-bearing behavior, the bond behavior of a material is crucial as well, the present paper deals with the bond fatigue of TRC with epoxy-impregnated carbon textiles. First, static tests are carried out to determine the sufficient anchorage length of the investigated material combination. Afterwards, the influence of cyclic loading on the necessary anchorage length, deformation, stiffness, and residual strength is investigated. The results of the cyclic tests are summarized in stress-number of cycles to failure (S-N) diagrams. In the end, it can be said that the cyclic loading has no negative impact on the necessary anchorage length. If specimens withstand the cyclic loading, there is no difference between their residual strength and the reference strength. The failure of specimens occurs only at high load levels, provided that the anchorage length is sufficient.

Sign in / Sign up

Export Citation Format

Share Document