An Investigation Into the Effect of Pre-bending on the Tube Hydro-forging Technology

Tube hydro-forging (THFG) combining with the pre-bending is an advanced method to manufacture the complex cross-sectional tubular component with curved axis. However, the effect of pre-bending on the subsequent THFG, especially on the critical internal pressure required to inhibit wrinkling, has not been clarified yet. Therefore, this paper makes a detailed study on it. At first, based on the energy method, the change rule between the critical internal pressure and the hoop strain was established when pre-bending was considered. Subsequently, the mechanics condition difference between single and double curvature differential segment during THFG was analyzed. Via the plastic theory, the distribution of hoop strain could be obtained. Mainly due to the uneven distribution of thickness and cold work-hardening caused by pre-bending, the maximum hoop strain at the outer straight-wall was greater than that at the inner straight-wall during THFG. Substituting the maximum hoop strain at the outer/inner straight-wall into the change rule, then their mathematical model of the critical internal pressure to restrain the wrinkling could be solved respectively. Finally, the critical internal pressure considering pre-bending was determined by that of outer straight-wall, and its value was always greater than the critical internal pressure without considering pre-bending under the same punch stroke. With the increase of bending radius, the critical internal pressure difference between considering and not considering pre-bending also increases. When the bending radius was 250 mm, the critical internal pressure difference was 33%, while it increased to 74% as the bending radius reduced to 100 mm, all of which were verified by experiment. The effect of friction coefficient on the critical internal pressure was also studied. In conclusion, this work provided a new and more accurate prediction model of critical internal pressure to guide practical production for when existing the pre-bending.

Experimental Study on Seepage Characteristics of Fractured Rock Mass under Different Stress Conditions

In order to obtain the mechanical behavior and permeability characteristics of coal under the coupling action of stress and seepage, permeability tests under different confining pressures in the process of deformation and destruction of briquette coal were carried out using the electrohydraulic servo system of rock mechanics. The stress-strain and permeability evolution curves of briquette coal during the whole deformation process were obtained. The mechanical behavior and permeability coefficient evolution response characteristics of briquette coal under stress-seepage coupling are well reflected. Research shows that stress-axial strain curve and the stress-circumferential strain curve have the same change trend, the hoop strain and axial strain effect on the permeability variation law of basic consistent, and the permeability coefficient with the increase of confining pressure and decreases, and the higher the confining pressure, the lower the permeability coefficient, the confining pressure increases rate under the same conditions, and the permeability coefficient corresponding to high confining pressure is far less than that corresponding to low confining pressure. The confining pressure influences the permeability of the briquette by affecting its dilatancy behavior. With the increase of the confining pressure, the permeability of the sample decreases, and the permeability coefficient decreases with the increase of the confining pressure at the initial stage, showing a logarithmic function. After failure, briquette samples show a power function change rule, and the greater the confining pressure is, the more obvious the permeability coefficient decreases.

The Influence Factors of Grain Integrity under the Internal Pressure Condition in SRM

To investigate the influence factors of propellant grain integrity under the internal pressure, the cylindrical grain was equivalent to a thick-wall cylinder and its three-dimension stress-strain problem was solved. Under the internal and external pressure, the strain and displacement equations of the inside thick-wall cylinder were expressed, and then, the stress and strain expressions of grain were obtained. On this basis, the hoop strain equations on the inside surface of the cylindrical grain and case were developed. The hoop strain on the inner surface of the grain can be predicted by the hoop strain of the case cylinder via the strain equations, and therefore, the hoop strain in the inner surface can be indirectly monitored in real time during the working process of the motor. The hoop strain in the inner surface of grain can be effectively reduced by increasing the case stiffness or decreasing the m number of the grain.

Incremental Forming of AA8006 Aluminum Alloys Sheet with Different Step Size

The main objects of this paper are to deal with the new technology of metal sheet forming using the incremental single-point tool to form the sheet metal. However, due to the needed long time to form the metal in incremental so that we used punching and then incremental forming to geometry the final shape of the product. By measuring the thickness and longitudinal strain and evaluating the hoop strain, it was noticed that the less depth in punching with less step size in incremental forming have a better strain effect in metal sheet forming. Keywords: Single point, incremental forming, Strain analysis, step size.

Multiphysics Modeling of Thorium-Based Fuel Performance With Cr-Coated SiC/SiC Composite Under Normal and Accident Conditions

Using the finite element multiphysics modeling method, the performance of the thorium-based fuel with Cr-coated SiC/SiC composite cladding under both normal operating and accident conditions was investigated in this work. First, the material properties of SiC/SiC composite and chromium were reviewed. Then, the implemented model was simulated, and the results were compared with those of the FRAPTRAN code to verify the correctness of the model used in this work. Finally, the fuel performance of the Th0.923U0.077O2 fuel, Th0.923Pu0.077O2 fuel, and UO2 fuel combined with the Cr-coated SiC/SiC composite cladding and Zircaloy cladding, respectively, was investigated and compared under both normal operating and accident conditions. Compared with the UO2 fuel, the Th0.923U0.077O2 and Th0.923Pu0.077O2 fuels were found to increase the fuel centerline temperature under both normal operating and reactivity-initiated accident (RIA) conditions, but decrease the fuel centerline temperature under loss-of-coolant accident (LOCA) condition. Moreover, compared to the UO2 fuel with the Zircaloy cladding, thorium-based fuels with Cr-coated SiC/SiC composite cladding were found to show better mechanical performance such as delaying the failure time by about 3 s of the Cr-coated SiC/SiC composite cladding under LOCA condition, and reducing the plenum pressure by about 0.4 MPa at the peak value in the fuel rod and the hoop strain of the cladding by about 16% under RIA condition.

Ratcheting assessment of corroded elbow pipes subjected to internal pressure and cyclic bending moment

The present study aimed to study ratcheting strains of corroded stainless steel 304LN elbow pipes subjected to internal pressure and cyclic bending moment. To this aim, spherical and cubical shapes corrosion are applied at two depths of 1 mm and 2 mm in the critical points of elbow pipe such as symmetry sites at intrados, extrados, and crown positions. Then, a Duplex 2205 stainless steel elbow pipe is considered as an alternative to studying the impact of the pipe materials, due to its high corrosion resistance and strength, toughness, and most importantly, the high fatigue strength and other mechanical properties than stainless steel 304LN. In order to perform numerical analyzes, the hardening coefficients of the materials were calculated. The results highlight a significant relationship between the destructive effects of corrosion and the depth and shape of corrosion, so that as corrosion increases, the resulting destructive effects increases as well, also, the ratcheting strains in cubic corrosions have a higher growth rate than spherical corrosions. In addition, the growth rate of the ratcheting strains in the hoop direction is much higher across the studied sample than the axial direction. The highest growth rate of hoop strain was observed at crown and the highest growth rate of axial strains occurred at intrados position. Altogether, Duplex 2205 material has a better performance than SS 304LN.

Experimental investigation of fiber Bragg grating hoop strain sensor–based method for sudden leakage monitoring of gas pipeline

Pipeline, serving as one of the most important gas transportation methods, can cause serious consequences in the event of leakage, so leakage monitoring is particularly important. In our previous study, a fiber Bragg grating hoop strain sensor was developed to detect pipeline leakage by measuring circumferential strain, and this sensor was utilized in a liquid pipeline leakage test to verify its performance. In this article, we established a full-scale gas pipeline model and investigated the performance of this fiber Bragg grating hoop strain sensor in leakage monitoring. On the basis of circumferential strain variation characteristic before and after negative pressure wave arrival at a fiber Bragg grating hoop strain sensor, a linear fitting algorithm combined with threshold detection was proposed to capture the knee point of circumferential strain. Test results illustrated that the proposed approach has good performance in knee point detection, and fiber Bragg grating hoop strain sensor is suitable for gas pipeline leakage monitoring.

Toward a Mechanistic Model of Stress Corrosion Cracking in PHWR Fuel Sheaths

This work builds on the iodine-induced stress corrosion cracking (ISCC) model of Lewis and Kleczek by integrating the fuel performance model fuel and sheath modeling tool (FAST) to provide thermal and mechanical analysis of the fuel sheath, which was previously required as input parameters. The iodine transport methodology of the Lewis–Kleczek model has been modified to utilize the more mechanistic diffusion model in FAST, and an empirical surface multiplier term has been derived to predict iodine release rates under normal operating conditions based on measured release rates from in-reactor sweep gas tests. A fracture mechanics analysis is implemented using threshold stress intensity values and crack growth rates reported in literature. A correlation to predict crack initiation has been derived by analysis of a database of power histories with known ISCC defects. This correlation is based on the change in sheath hoop strain during a power ramp and is shown to be more accurate at discerning failure versus nonfailure than the correlations used in the previous Lewis–Kleczek model and FUELOGRAMS. Failure time prediction of the model is compared against power ramp test FFO-104 performed at the National Research Experimental (NRX) reactor. Fuel failure is predicted to occur 27% faster than experimentally measured; failure time is explored in a series of sensitivity studies to suggest areas for further development. The model improvements represent a step forward in the mechanistic modeling of stress corrosion cracking (SCC) in pressurized heavy water reactor (PHWR) nuclear fuel.

Microwave Chipless Resonator Strain Sensor for Pipeline Safety Monitoring

Real-time hoop strain monitoring is known as an important parameter for the evaluation of pipeline safety and integrity. Internal corrosion and consequently variation of wall thickness directly reflects in hoop strain variation. In addition, leakage causes a pressure drop and strain reduction due to negative pressure wave. Due to their promising features such as extremely low cost, relatively high sensitivity, compatibility with harsh environmental conditions, distant and non-contact sensing with negligible power consumption, microwave resonator-based sensors achieved great deals of interest during the last decade. In this work, a chipless flexible microwave sensor for pipeline hoop strain real-time monitoring is presented. The sensor structure comprises a flexible chipless split ring microwave tag resonator attached to the pipeline and electromagnetically coupled to a pair of gap coupled transmission lines form the reader located at a certain distance from the tag strain sensor. Strain variations as the results of the mentioned pipeline defects change the overall length of the attached tag sensor which consequently causes a shift in its resonance frequency. For assuring the tag sensor to mechanically follow the strain variation of the pipeline, the Young modulus of its structural material should be much lower than that of the pipeline. This condition also important for the integrity of the sensor-pipe system because their connection will be accomplished by an adhesive. Since copper as the standard microwave conductive material is relatively highly stiff, it is not an appropriate candidate for such an important application. For addressing this issue, the chipless tag structure is fabricated by a conductive rubber layer in this work with extremely low Young modulus guaranteeing the length of the tag strain sensor to exactly follow the strain variation of the pipeline and forms a reliable and precise pipeline strain sensor. The spectrum of the tag sensor is reflected on the reader structure spectrum which could be measured to monitor the resonance frequency shift of the tag resulted from length variation of the tag sensor directly related to the pipeline strain fluctuation.