Influence of stresses on deformation process under the irradiation creep and swelling

Approaches for describing the deformation of structural elements made from the material, in which radiation creep and swelling strains develop simultaneously, are discussed. The technique for description of irradiation swelling strains, which is used for calculational analysis of stress-strain state arising in structural elements under the joint action of irradiation and thermal-stress fields, is regarded. A complete system of equations of the boundary –initial value problem is presented, in which elastic and thermal strains, strains of radiation creep and swelling are taken into account. Numerical modelling was carried out using the specialized software FEM Creep, in which the boundary value problem is solved by the Finite Element Method, and the initial one is integrated in time by the difference predictor-corrector method. Two forms are given for the equation of state describing the radiation swelling strains: first is for the components of the strain tensor as well as second is prepared for their rates. The hypothesis about the linear correspondence of the received radiation dose and the deformation time, during which radiation swelling strains develop, are analyzed. A number of questions that require answers when using equations with a complex stress state in which the radiation swelling strains are directly depend on stresses, are discussed. Based on the processing of experimental data on the swelling of tubes made of steel 316Ti in the temperature range of 450-460 °С, a form of the equation for the radiation swelling strain rate is proposed, and the constants included in it are determined. Using the example of numerical modelling of the deformation of tubes were made of steel 316Ti and loaded by inner pressure, the applicability of the classical approach for the analysis of the stress-strain state in the presence of radiation swelling strains is shown.

The Effect of Temperature on Dynamic Characteristics of Frozen Clay under Principal Stress Rotation

The foundation soil is always subjected to complex stress, including continuous rotation of the principal stress caused by traffic and earthquake loads. To comprehend the dynamic characteristics of frozen clay under complex stress sate, including continuous rotation of the principal stress, this study investigates the effect of temperature on the dynamic characteristics of frozen clay under principal stress rotation using a frozen hollow cylinder apparatus (FHCA-300). The test results reveal that the cumulative plastic strain of frozen clay samples exponentially increases with the rising of temperature under principal stress rotation. The influence of temperature is more profound with a high cyclic stress ratio (CSR). A decrease in temperature can improve the stiffness of the frozen clay, reduces its energy dissipation, and enhances its ability to resist dynamic loading. However, the principal stress rotation phenomenon may aggravate the damage of frozen clay and increase the energy dissipation and reduces its ability to resist dynamic loading. Based on the experimental data, an empirical expression was proposed to describe the coupling influence of CSRs and temperature on the axial resilient modulus of frozen clay, which can predict the development of axial resilient modulus under different thermal-mechanical conditions.

Young and Old Leaves Physiological and Metabolite Profiles Analysis on Amino Acids and Organic Acids in Wild Soybean Seedlings Under Nitrogen Deficiency

Background As an important germplasm resource, wild soybean has good tolerance to complex stress environment stress. This study described the differences of physiological and metabolomic changes between common wild soybean (GS1) and the barren tolerance wild soybean (GS2) under low nitrogen (LN) stress. Results The result showed the barren tolerance wild soybean young leaves can maintain relatively stable chlorophyll content and increased the contents of Car;Photosynthetic rate and transpiration rate decreased significantly in in the barren tolerance wild soybean old leaves, but there was no significant change in young leaves; the barren tolerance wild soybean enhanced the enrichment of beneficial ion pairs such as zinc, calcium and phosphorus. The metabolism of amino acids and organic acids in the barren tolerance wild soybean old leaves was vigorous, a large number of beneficial amino acids such as GABA, asparagine and proline were enriched, and the metabolites related to TCA cycle were significantly increased. Conclusion the barren tolerance wild soybean can ensure the nitrogen supply of young leaves by inhibiting the photosynthetic response of old leaves; the relatively stable growth of young leaves also benefits from the effective transport and reuse of beneficial ions from old leaves; More importantly, the enhanced metabolism of specific amino acids and organic acids in GS2 old leaves seemed to play an important role in resisting LN stress. GABA and Asparagine played substantial roles in N storage, C/N balance, antioxidant defense and act as signaling molecule to help GS2 to resist LN stress. Difference organic acids in the old leaves of GS2 increased which could improve the utilization rate of N in the soil. In addition, the strength of fatty acids catabolism and TCA cycle in GS2 old leaves provided energy base for substance transport. The analysis of physiological and metabolite may provide a new perspective for revealing the importance of substance transport and reuse in different plant parts to resist abiotic stress.

Investigation of the Energy Evolution of Tectonic Coal under Triaxial Cyclic Loading with Different Loading Rates and the Underlying Mechanism

It is of great significance to ascertain the mechanical characteristics and deformation laws of tectonic coal that is under complex stress conditions for safe production, but the targeted research in this area is still insufficient at present. This paper performed triaxial tests under cyclic multi-level loading at different rates by using an MTS-815 Rock Mechanics Testing System. The strain characteristics, elastic modulus and energy evolution were obtained in order to explore the effects of the mechanism of loading rate on the evolution of deformation and energy parameters of tectonic coal. The results showed that the irreversible strain and plastic energy increased exponentially with the increase in the deviatoric stress, but the growth rate decreased with the increase in loading rate. Furthermore, the elastic strain increased linearly and the growth rate was essentially unaffected by the loading rate. During the compaction stage, the variation of each parameter was not sensitive to the loading rate; during the elastic and damage stage, the rate increase inhibited secondary defect propagation and improved rock strength. In addition, the stepwise and cumulative energy ratio was defined in order to describe the energy distribution during cyclic loading and unloading. It was found that the decrease in the loading rate was beneficial to the transformation of the total energy into plastic energy. The elastic modulus was the most sensitive to sample damage, but the energy density evolution was able to be used to describe the deformation damage process of tectonic coal in more detail. These findings provide important theoretical support for the tectonic coal deformation law and action mechanism in the damage process that occurs under complex stress conditions.

Reliability Analysis of CFRP-Packaged FBG Sensors Using FMEA and FTA Techniques

Carbon fiber-reinforced plastics (CFRP)-packaged fiber Bragg grating (FBG) sensors are widely used in full-scale structural testing of wind turbine blades (WTBs). However, the specific process to make CFRP-packaged FBG sensors, such as packaging, bonding, welding, etc., are mainly manually operated, and no unified standard or rule has been formed yet. Non-standard specific processes, coupled with complex stress distribution, unstable working environments, etc., result in the CFRP-packaged FBG sensors having various failures with time, resulting in inaccurate measurements. Thus, the need to carry out related failure analysis is urgent. This paper therefore performed a reliability analysis for CFRP-packaged FBG sensors using failure mode and effects analysis (FMEA) and fault tree analysis (FTA) techniques. The results provide an important basis towards analyzing performance degradation and functional failures for CFRP-packaged FBG sensors.