Average Tensile Stress Research Articles

Effect of porous defects on mechanical behavior of functionally graded materials

Porous defects in functionally graded materials (FGMs) significantly change their mechanical behavior, in particular, affecting the displacement of the neutral plane and stress distribution. Defects such as porosity reduce material bending strength while enhancing compression strength and can lead to significant transverse effects. The purpose of this study is to clarify the influence of porosity on transverse effects based on new kinematic model. This research consider in detail a particular case of this model, that allows take into account two Poisson`s effects separately. This study examines the influence of porosity on FGM, highlighting the critical role of changes in Poisson’s ratio through thickness. The theory used for analytical solution satisfies the nullity of the shear stresses at the upper and lower surfaces of the plate without using the shear correction factor. The network of pores proposed to be empty or filled with low-pressure air and material properties graded by thickness according to power-law and exponential models. Navier solution method is used to solve the governing differential equations of equilibrium. The concentration of porosity at the center of the plate or in separate layers results in a reduction in normal tensile stresses along the longitudinal coordinate, suggesting that strategic placement of porosity can be used to reduce stress concentrations, potentially enhancing the structural integrity and performance of functionally graded materials under mechanical loading.

The thermal responses of composite box girder bridges with corrugated steel webs under solar radiation

Owing to the direct exposure to complex atmospheric environments, the temperature field of composite box girder bridge with corrugated steel webs (CBGB-CSW) is likely non-uniformly distributed. Whereas, the current researches regarding the thermal responses of CBGB-CSW are insufficient, and the thermal responses of CBGB-CSW under solar radiation are still unknown. Therefore, this paper conducted a long-term temperature experiment on a scaled model to explore the temperature distribution characteristics in CBGB-CSW. Meanwhile, a three-dimensional thermal–mechanical coupling Finite Element (FE) model is established to simulate the temperature field in the experiment girder. The accuracy and effectiveness of the developed FE model has been verified by the measured temperature data. Therewith, the thermal responses (i.e., stress and displacement) of a full-scale continuous CBGB-CSW with a span of 150 m are numerically investigated. The results indicate that the maximum stresses always occur at the midspan section (with a depth of 5 m) of the continuous CBGB-CSW, and considerable concentrations of stress are observed in the steel-concrete junction. The maximum longitudinal tensile and compressive normal stresses within 0.4 m of the upper junction can reach 5.55 MPa and −8.46 MPa respectively, and those of the lower junction can reach 6.96 MPa and −7.05 MPa respectively. Besides, owing to the impacts of vertical and horizontal temperature gradients, significant displacements of the whole bridge can also be observed. The maximum vertical displacement (5.33 mm) of the CBGB-CSW is estimated at the top plate in the midspan, while the maximum horizontal displacement (0.74 mm) is estimated at the trough of the southern corrugated steel web in the midspan. Notably, the outcomes of this paper can provide some useful references for engineers and scholars to understand the thermal responses of the CBGB-CSW.

Mechanical evaluation of human cadaveric lumbar soft tissues suggests possible physiological stress shielding within musculoskeletal soft tissues by the thoracolumbar fascia.

This study investigates the potential for stress shielding within musculoskeletal soft tissues through analysis of stress distributions between lumbar fascial and muscle tissues via mechanical testing. Using a custom apparatus, 51 posterior thoracolumbar fascia (TLF) samples and 18 erector spinae (ES) cadaveric samples underwent tensile testing involving three loading-unloading cycles, followed by loading to 6% strain, to mechanically characterize samples. Parallel tensile testing using 20 pairs of two TLF samples, and seven pairs of TLF and ES samples was then conducted for stress distribution analysis between tissues. P<0.05 was deemed significant. The TLF and ES exhibited an average elastic modulus of 150.9MPa and 0.6MPa, respectively. At 6% strain, parallel testing of the TLF pairs yielded an average tensile stress of 8.4MPa and 1.7MPa (p<0.001) exhibited by the stiffer and less stiff TLF samples, respectively. Similarly, TLF-ES parallel testing resulted in average tensile stresses of 7.1MPa and 0.07MPa of the TLF and ES (p<0.002). Results suggest elevated loading towards stiffer TLF samples relative to less stiff TLF and ES samples. In soft tissues affected by LBP, skewed stress distributions may result in the TLF withstanding the majority of stress, yielding cyclical stress shielding that may contribute to and/or promote LBP. This novel study demonstrates a potential load allocation bias towards the TLF, laying the foundation for stress shielding within lumbar musculoskeletal soft tissues affected by degenerative musculoskeletal conditions.

Study of the Effect Launching System using Airbags on the Hull Structures of Pinisi Ship

Using airbags for ship launching is a technological innovation with promising implications for the shipbuilding industry. Considering the inefficiency and time consumption of the traditional Pinisi ship launching method, an airbags system is considered an alternative technology. This research involves a simulation of applying airbag technology for ship launch on the Pinisi Ship to assess stress concentration and magnitude. The Pinisi ship, airbags, and skates are designed in three dimensions on a real-size scale for analysis and then analysed using Finite Element Analysis (FEA) in ANSYS software. During the launch, the keel of the ship and airbags were subjected to a compressive force with a 3-millisecond analysis time. The stress and stress concentration levels in the Pinisi ship's structure vary between using airbags and the traditional launch method during launch. The ship's engine room bulkhead and the bow collision bulkhead structure underwent considerable tensile and compressive stresses in longitudinal and transverse orientations. The average maximum compressive stress and maximum tensile stress that occur in the longitudinal direction of the ship are around 50.2 MPa and 87.3 MPa, respectively. Compared to the maximum compressive stress, which accounts for 36% of the overall maximum stress encountered, the highest tensile stress experienced by the ship's structure is 64%.

Influence of shielding gas flow on the TIG welding process using stainless steel 304 material

A common issue encountered with main heat exchanger equipment is improper operation, which can lead to the development of cracks in the stainless-steel pipes. The welding process alters the metal microstructure in the heat-affected zone, thereby affecting the mechanical properties of the welded joint. To mitigate this issue, TIG welding with argon shielding gas is employed. This method helps prevent oxidation and ensures the formation of a stable welding arc in 304 stainless steel, which is renowned for its excellent mechanical properties and corrosion resistance. The objective of this study is to evaluate the impact of variations in shielding gas flow on the mechanical properties of 304 stainless steel plates during the TIG welding process. The aim is to determine the optimal settings for producing robust and long-lasting welded joints. To assess the hardness of the welded joints, we employed a Brinell-type Hardness Tester FB-3000LC machine. A Brinell steel ball indenter measuring 5 mm on the HBW scale and applying a load of 125 Kgf was utilized. At a protective gas flow rate of 8 L/min, the average tensile stress was 44.72 N/mm², strain was 0.177, modulus of elasticity was 2518 MPa, and hardness was 99.712 HBW. Increasing the gas flow rate to 13 L/min resulted in an average tensile stress of 47.50 N/mm², strain of 0.189, elastic modulus of 2525 MPa, and hardness of 105.522 HBW. Further increasing the gas flow rate to 18 L/min led to an average tensile stress of 49.69 N/mm², strain of 0.192, modulus of elasticity of 2597 MPa, and hardness of 106.704 HBW. Based on the research findings, it was observed that the weld area exhibited an increase in hardness values due to the heat generated during the welding process. The use of protective gas flow during welding is deemed effective in producing well-formed welded joints, as it prevents fractures from occurring within the weld area during the tensile test process. The choice of protective gas is determined by the dimensions of the material plate.

Thermally stressed state of asphalt concrete layer on a metal base

The results of a finite element study of the thermally stressed and deformed states of a fragment of a two-layer bridge structure, consisting of a bearing metal orthotropic slab with a layer of asphalt concrete applied on it, are presented. It is believed that the materials of the layers are characterized by different thermomechanical parameters, which determine the inhomogeneity of the stress and strain fields. An analogue of these phenomena can be the effect of transformation in electric thermal relays of thermal action on a bimetallic plate with different coefficients of thermal linear expansion into its mechanical displacements, which are used to actuate the switch and switches. Using the method of computer modeling, it was found that these factors lead to the concentration of stresses and strains and changes in the stress-strain state in all elements of the bridge structure end are not taken into account in the modern practice of designing and operating bridges, as well as are one of the reasons for the premature destruction of asphalt concrete pavements. To eliminate these shortcomings, on the basis of finite element algorithms, a theoretical analysis of the thermally stressed state of a metal bridge slab with an asphalt concrete pavement at various ratios of their thicknesses is carried out. It is shown that an increase in the thickness of the upper layer can lead to an increase in shear and normal tensile stresses initiated in it. Therefore, when designing bridge structures, these features should be additionally taken into account.

The effect of imperfect bonding on stress distribution in fibrous composites

An attempt was made to map the distribution of stress in fibrous composites with imperfect bonding. Two analytical micro-mechanics models were developed. In the first model, the composite was subjected to axial tensile loading, parallel to the fiber direction, and the assumption of iso-strain was employed to derive the control equations. In the second model, the composite was loaded in the direction transverse to the fiber. An iso-stress condition was employed, and Airy stress function was utilized to articulate the stress and displacement equations. An assumption of how the stress is transferred between the matrix and the fiber was introduced in both models. To investigate and validate the models, specimens were fabricated using a carbon plain weave fabric and a geopolymer matrix. Single fiber pullout and three-point bending tests were carried out. The maximum average tensile stress obtained from the three-point bending tests, as well as the mechanical properties of the fiber and geopolymer, served as input for the models. Results indicate that the effect of the level of bonding is very high in the transverse direction while almost negligible in the axial direction. The difference in the maximum value of the axial tensile stress at the fiber-matrix interface was used to calculate the numerical value of the interfacial shear strength, and the numerical result matched the data obtained from the single fiber pullout test.

Influence of different wet-blasting pressure on the surface integrity and tool cutting performance of hybrid CVD-TiN/TiCN/α-Al2O3/TiN coated tools

This paper investigates the effect of wet-blasting pressure on the surface integrity and tool cutting performance of hybrid CVD-TiN/TiCN/α-Al2O3/TiN coated tools. The hybrid TiN/MT-TiCN/α-Al2O3/TiN multilayer coating was deposited on the surface of the cemented carbide inserts by chemical vapor deposition (CVD) technique. Then the coated inserts were subjected to wet-blasting by aluminum oxide with varying pressure. The coatings were characterized by scanning electron microscopy, white light surface profiler, and X-ray residual stress diffractometer. The results indicate that the average residual tensile stress of the α-Al2O3 layer on the rake face of CVD-coated inserts gradually decreased with the increase of wet-blasting pressure. When the wet-blasting pressure reached 0.24 MPa, the residual tensile stress was transformed into compressive stress. It was accompanied by increased cutting edge roughness and cutting edge radius, reduced cutting edge coating thickness, and a change in rake face surface roughness. To understand the effect of the surface integrity change on the cutting performance of CVD-coated inserts, a case study designed for AISI 4340 steel machining under continuous and intermittent cutting conditions is performed. When the Al2O3 layer on the cutting edge is not peeled off by wet-blasting, the change of residual stress from tensile to compressive in the rake face of CVD-coated inserts can effectively improve the fracture failure resistance of inserts in continuous and intermittent cutting processes. When the Al2O3 layer on the cutting edge is peeled off by wet-blasting, the fracture failure resistance during intermittent cutting will be significantly reduced.

ВЛИЯНИЕ ТОЛЩИНЫ ПОПЕРЕЧНОГО И ПРОДОЛЬНЫХ СЛОЕВ НА ДЕФОРМАЦИИ И НАПРЯЖЕНИЯ В 3-СЛОЙНОЙ ПЛИТЕ ДПК (CLT), СМОДЕЛИРОВАННОЙ КАК СОСТАВНАЯ ПЛАСТИНА

The study examines the effect of the transverse and longitudinal layers thickness of a three-layer CLT panel on the deformations and distribution of the resulting tensile and compressive normal stresses in the layers. Due to the current lack of a unified methodology for the calculation of multilayer materials with orthotropic properties in layers at present, we carried out the study with the SCAD+ computing complex using the finite element method. The studied model was a composite orthotropic plate. The authors obtained, systematized and clearly showed the dependences of the values of the maximum deflection and normal stresses on the thickness variation of transverse and longitudinal lamellae in a three-layer CLT panel under different boundary conditions. As a result of the study, we found that the greatest influence on the deflection and normal stresses along the span was caused by the longitudinal slab layers. The results provide a better insight into the relationship between deformability and stress distributions and the variation of transverse and longitudinal layer thicknesses. The obtained patterns can be used in the design of building structures using CLT panel.

Experimental investigation of axial tensile and fatigue behaviors of HTS round strands

For the development of high-temperature superconducting (HTS) magnet systems of future fusion devices, a novel HTS round strand based on a stacking structure was designed and manufactured using second generation (2G) HTS tapes. Different mechanical loads during operation can result in irreversible degradation of the strand. The axial tension and fatigue loads need particular attention. Therefore, it is important to investigate the electromechanical behavior of the round strand under various axial tension and cyclic loads. In this paper, the axial tensile and fatigue tests were conducted at 77 K, self-field. Taking 95% critical current (Ic) retention as the criterion, the results of the tensile tests revealed that the average tensile stress and strain were as high as 344 MPa and 0.47%, respectively. Fatigue characteristics were also investigated as a function of axial tensile stress. No significant performance degradation was observed up to 100,000 loading cycles with stress amplitudes ranging from 20 MPa to 200 MPa. Ic degradation occurs after 16,000 loading cycles with 380 MPa as the maximum stress. Furthermore, the microscopic defects of the round strand samples due to fabrication imperfections and mechanical loading were investigated using metallographic microscope and scanning electron microscope. These results presented in this paper are useful for comprehending and improving the mechanical behaviors of the strand in high-field and large-scale fusion magnet systems.

Numerical investigation of intra-abdominal pressure and spinal load-sharing upon the application of an abdominal belt

Chronic low back pain patients may experience spinal instability. Abdominal belts (ABs) have been shown to improve spine stability, trunk stiffness, and resiliency to spinal perturbations. However, research on the contributing mechanisms is inconclusive. ABs may increase intra-abdominal pressure (IAP) and reduce paraspinal soft tissue contribution to spine stability without increasing spinal compressive loads. A finite element model (FEM) of the spine inclusive of the T1-S1 vertebrae, intervertebral discs (IVDs), ribcage, pelvis, soft tissues, and abdominal cavity, without active muscle forces was developed. An identical FEM with an AB was developed. Both FEMs underwent trunk flexion. Following validation, the models’ intervertebral rotation (IVR), IAP, IVD pressure, and tensile stress in the multifidus (MF), erector spinae (ES), and thoracolumbar fascia (TLF) were compared. The inclusion of an AB resulted in a 3.8 kPa IAP increase, but a decreased average soft tissue tensile stress of 0.28 kPa. The TLF withstood the majority of tension being transferred across the paraspinal soft tissues (>70 %). The average IVR in the AB model decreased by 10 %, with the lumbar spine experiencing the largest reduction. The lumbar IVDs of the AB model likewise showed a 31 % reduction in average IVD pressure. Using an AB improved trunk bending stiffness, primarily in the lumbar spine. Wearing an AB had minimal effect on reducing tensile stress in theES. The skewed stress distribution towards the TLF suggests its large contribution to spine stability and the potential advantage in unloading the structure when wearing an AB, measured herein at8 %.

Experimental study of erosion behavior under fluctuating tensile loads

When studying the erosion behavior of fracturing pipelines, it is inevitable to consider the exacerbating effect of fluctuating internal pressure on pipeline erosion damage. Therefore, an erosion experimental apparatus capable of applying fluctuating tensile loads to specimens was developed to investigate the erosion rate of 35CrMo steel at different average tensile stresses (0–500 MPa), impact angles (15–90°), flow velocity (7.5–20 m/s), and experimental times (10–60 min), and to analyze the erosion damage mechanism under fluctuating loads by observing the microstructure within the erosion scars using scanning electron microscope. The results indicated that erosion rate increased up to 36.84% compared to that without loading under the same erosion condition. Erosion rate increased up to 822.00% when velocity increased from minimum to maximum. Under fluctuating loads, the deepest part of the erosion scar cracked first and the specimen eventually fractured completely along with its entire width, demonstrating that the newly established experimental conditions can well reproduce the sudden bursting phenomenon common to high-pressure pipelines that erode under harsh conditions. The fracture of the specimen shows laminar structure, which is a typical damage feature resulting from the combined effect of a great number of tensile stress cycles and erosion wear.

Study of The Potential of Palm Oil Empty Core Fiber As Composite Materials for Ship Hull

Palm oil is the largest commodity in Indonesia. Pprocessing of oil palm, leaving 20% to 23% empty palm fruit bunches (EFB). Oil palm empty fruit bunches (EFB) is a collection of fiber left behind after separating the fruit from fresh fruit bunches that have been sterilized. Some researchers use natural fibers as an alternative for making composites. This study aims 1. To determine the tensile strength of the alternative material of palm empty fruit bunch fiber. 2. To determine the buckling or bending strength of the alternative fiber material for empty palm oil bunches. The method used is the tensile and bending test method in the process of mixing the fiber material of empty palm oil bunches in the manufacture of composites. The test results obtained were compared with the BKI composite standard. The volume fraction used in this study was 30% polyester resin and 70% EFB fiber, 40% polyester resin and 60% EFB fiber and 50% polyester resin and 50% EFB fiber with NaOH alkaline treatment for 2 hours. The average tensile stress values obtained for each fraction were 27.372 MPa, 24.168 MPa and 25.875 MPa respectively. The values for the bending stress of each fraction are 144.836 Mpa, 149.059 Mpa and 164.682 Mpa respectively.

Tensile and Flexural Behaviors of Basalt Textile Reinforced Sprayed Glass Fiber Mortar Composites.

The proposed study combines sprayed glass fiber-reinforced mortar and basalt textile-reinforcement to harness the favorable properties of each component to obtain a composite material that can be used for strengthening of existing structures. This includes crack resistance and a bridging effect of glass fiber-reinforced mortar and the strength provided by the basalt mesh. In terms of weight, mortars containing two different glass fiber ratios (3.5% and 5%) were designed, and tensile and flexural tests were conducted on these mortar configurations. Moreover, the tensile and flexural tests were performed on the composite configurations containing one, two, and three layers of basalt fiber textile reinforcement in addition to 3.5% glass fiber. Maximum stress, cracked and uncracked modulus of elasticity, failure mode, and average tensile stress curve results were compared to determine each system's mechanical parameters. When the glass fiber content increased from 3.5% to 5%, the composite system without basalt textiles' tensile behavior slightly improved. The increase in tensile strength of composite configurations with one, two, and three layers of basalt textile reinforcement was 28%, 21%, and 49%, respectively. As the number of basalt textile reinforcements increased, the slope of the hardening part of the curve after cracking clearly increased. Parallel to the tensile tests, four-point bending tests showed that the composite's flexural strength and deformation capacities increase as the number of basalt textile reinforcement layers increase from one to two.

Gas fracturing behavior and breakdown pressure prediction model for granite under different confining pressure and injection rate

Conventional hydraulic fracturing techniques are often found problematic for extracting geothermal energy in hot dry rock (HDR). As an alternative, employing the less viscous gas to replace water as the fracturing fluid showed great potential for more effective fracturing of HDR. In this work, the failure behavior and mechanism of granite during gas fracturing under different confining pressures and gas injection rates are comprehensively examined. It is shown that the breakdown pressure increases with the increase of confining pressure, whereas higher gas injection rate can result in evident decrease of the breakdown pressure. As the confining pressure grows, the acoustic emission (AE) event increases rapidly, with much higher AE counts observed at high gas injection rates than at low injection rates. Comparatively, the AE energy decreases under high confining pressure, due probably to granite transitioning from brittle to ductile. It is interesting that the b-value of AE varies dramatically as the gas injection rate becomes higher with significant fluctuations, indicating the ratio of large fracture and small fracture changes drastically during gas fracturing. In addition, the length of the induced fractures decreases with the increase of confining pressure during gas fracturing, and the length and width of vertical fractures are evidently larger when at high gas injection rate. Last, a novel theoretical predictive model is proposed for estimating breakdown pressure during gas fracturing based on the average tensile stress criteria, which is featured by considering the effect of confining pressure and gas flow behaviors. The theoretical prediction agrees with the experimental results. The present study can provide valuable results for theoretical analysis and engineering applications of gas fracturing in stimulating the HDR reservoirs.

STUDY OF THE ROLLING PROCESS WITH TECHNOLOGICAL LUBRICANT AT SINGLE-ZONE SLIPPING METAL IN THE ZONE OF DEFORMATION

One of the controversial provisions the rolling theory is the question of the possibility the stable process of cold rolling with lubrication at a complete lag of the strip’s metal in the deformation zone, i.e. in conditions of negative advancing.&#x0D; The equilibrium state in the zone of deformation with negative advance can be maintained due to the change in the thickness of the lubricating film. This is evidenced by experimental data from the study of the dependence of the advancing and the thickness of the lubricant layer on the grip angle during cold rolling with castor oil the copper samples in sizes 5x60 mm. Rolling was carried out on a duo 180 laboratory mill in steel rolls with a diameter of 190 mm. The rolling speed was 0.35 m/s.&#x0D; Then stress state modeling is used to theoretically substantiate the possibility of a stable process with single-zone sliding of metal in rolls during cold rolling with effective technological lubricants. According to Newton's law, the frictional forces acting in the zone of deformation depend on the sliding speed of the metal on the rolls and on the thickness of the lubricating film.&#x0D; Substituting the chooses model of specific friction forces into T. Karman's differential equation of equilibrium and solving it under known boundary conditions, expressions for the distribution of contact stresses were obtained.&#x0D; The results of calculations in the conditions of contact-hydrodynamic friction prove that the maximum of normal pressure shifts closer to the entrance to the deformation zone. In the case of rolling with a negative advancing, the longitudinal normal tensile stresses occur near the cross-section at the exit of the metal from the rolls. The average pressure in the deformation zone is always greater than the forced yield strength for the rolling strip.&#x0D; With an increase in the lag of the metal from the rolls at the exit from the zone of deformation, the average pressure decreases. Rolling with single-zone strip sliding is an energy-efficient process.

Regularities of Changing the Limiting Values of Stress and Strain Invariants in Microinhomogeneous Media

By using nonlinear equations of constraints between macro- and micro-states, the regularities of changes in the limiting values of stress and strain invariants in microinhomogeneous media are studied. It is shown that the extreme relative moduli of stress tensor deviators in polycrystals with a cubic lattice are invariant with respect to external conditions of reversible force and depend only on the crystal anisotropy factor. In the irreversible region of deformation, analytical relations are obtained for bulk and tensile normal stresses. The effect of cyclic change in bulk and tensile stresses in some subelements under external monotonic loading has been established. It is shown that, on the basis of nonlinear equations of constraints, a complex pattern of material failure can be described using the theory of maximum normal stresses at the local level.

A Study of Residual Stresses in Steel Plates Obtained by Laser Deposition Directly on a Rigid Substrate

A neutron diffraction method has been used to study residual stresses in corrosion-resistant martensitic steel AISI 410 plates of the composition (wt %): 0.15 С, 13 Cr, 1 Mn, 1 Si, and Fe for balance obtained by direct laser deposition. The plates are deposited on rigid substrates, which are commonly used in practice in the production of large parts. It has been shown that in plates of different thicknesses (2.2 and 7.4 mm) and the same length and width (70 × 30 mm), the patterns of the stress distribution curves are very close, however, the stresses in a 7.4-mm-thick plate are lower than in a 2.2-mm-thick plate. In both plates (2.2/7.4 mm), the maximum normal tensile stresses (~450/350 MPa) are induced near lateral edges of the substrate. The maximum tensile longitudinal stresses (~400/250 MPa) are induced in the middle section of the plate near the upper edge. In the middle section of a 7.4-mm-thick plate, a stress distribution over the thickness is observed: the stresses near the side surfaces are higher than in the middle section. The thickness distribution becomes more uniform by approaching the plate edges. The stress distribution pattern in plates obtained by direct laser deposition strongly depends on the rigidity of the substrate and, to a lesser extent, on the material and deposition technology.

Chloride penetration resistance of engineered cementitious composite (ECC) subjected to sustained flexural loading

This paper presents a research on the chloride penetration behavior of engineered cementitious composites (ECC) under sustained flexural loads. Three load levels, i.e. 30 %, 60 % and 75 % of the ultimate flexural load were used. Chloride diffusion depth and concentration profile were measured 30, 60 and 150 days after the specimen was exposed to NaCl solution and compared with pre-loaded specimens. Influence of the sustained local bending stress and microcracks were investigated. It shows that under sustained loads, the relationship between the surface chloride content and maximum normal tensile stress can be described using an exponential equation. A binary model was developed to explain the correlation among the chloride ion diffusion coefficient, maximum normal tensile stress and exposure time. Changes of capillary pore structure and phase compositions were measured using mercury intrusion porosimeter and X-ray diffraction, respectively. Unlike mortar, the fiber bridging of ECC helps with limiting crack width and thus the diffusion process, and the measured results were used to explain the observed penetration behavior of ECC. It is believed that the current study provides theoretical foundation for the durable design of the ECC/concrete composite structure.

Numerical analysis on the thermal mismatch stress of quasi-isotropic strand with square cross section during cool-down

The quasi-isotropic strands (Q-IS) with high current-carrying capacity can effectively improve the anisotropy of the critical current in the magnetic field. However, when a quasi-isotropic strand is cooled from room temperature (300 K) to the liquid helium temperature (4.2 K), it may cause the irreversible degradation of the critical current, the plastic deformation, and even mechanical damage. In order to achieve the safe and stable operation of quasi-isotropic strands, it is important to analyze the thermal mismatch stress during cool-down. In this study, two mechanical models (i.e. a bulk model and a contact model) were developed by considering different material elastoplastic characteristics to study the mechanical behaviors of quasi-isotropic strands with square cross section in the cooling process. Compared with the bulk model, the contact model can simulate the contact and separation between adjacent REBCO conductors in quasi-isotropic strands. Therefore, the contact model should be chosen to estimate the thermal mismatch stress of quasi-isotropic strands during cool-down. In addition, plastic deformation was clearly observed in the Cu and Ag layers with peak equivalent plastic strains of 0.016% and 0.171%, respectively. When the stainless steel sheath is replaced by the copper sheath to encase a quasi-isotropic strand, the interlaminar normal tensile stress between the superconducting layer and Hastelloy substrate was decreased from 101 MPa to 16.2 MPa. Therefore, a quasi-isotropic strand encased in a copper sheath could reduce the risk of delamination during cool-down.