The normal stress of each layer of the laminate composite material will undergo complex changes after normal compression, and shear stress will also appear between the layers. In order to explore the ...distribution laws of normal stress and shear stress, this paper uses Hooke's law and the equilibrium condition of force to carry out mathematical derivation, the analytical formulas for normal stress and shear stress are obtained, and their respective maximum values are given. Studies have shown that the maximum normal stress occurs at the center of the laminate, and its value is proportional to the external load, and is also closely related to the length, width, thickness, elastic modulus of the cementing agent, elastic modulus and Poisson’s ratio of the laminate; The maximum shear stress occurs at the four corners of the laminate, and its value is proportional to the external load and the shear modulus of the cementing agent, inversely proportional to the thickness of the cementing agent layer, and its value is also closely related to the length, width, elastic modulus and Poisson's ratio of the laminate. The analytical formulas for normal stress and interlayer shear stress is helpful to deepen the understanding of the internal force distribution law of laminated plates, and the maximum value calculation formula can greatly facilitate the calculation of strength.
A compound-forming method that combines multi-pass stretching and induced electro-pulsing treatment (IEPT) is proposed. The effects of induced current on the microstructure and mechanical properties ...of material were investigated using transmission electron microscopy and electron backscatter diffraction measurements. The samples stretched by 5% each time showed 145% increase in elongation after 4 stretching and IEPT cycles. The IEPT caused “stress drop” in pre-deformed sheets, while the plasticity increased. Meanwhile, the dislocation density decreased, the deformation structure changed to the substructure, and the grain size increased slightly. The material anisotropy was reduced and a new 《111》//TD texture appeared after IEPT. The combination of electrical effect and Joule heating enhanced dislocation mobility and vacancy movement. The temperature distribution, with a maximum temperature reaching 144.7 °C, was simulated using ANSYS software. The theoretical calculation results were consistent with experimental data.
This paper presents a comprehensive numerical study on the combined compression-bending performance of concrete-filled steel tubes (CFSTs) considering the commonly seen localised pitting corrosion ...damage in the marine environment. An advanced finite element modelling technique is utilised to simulate the localised corrosion pits on the outer surface of the steel tube considering its random nature. The differences between the load-moment interaction of CFSTs with uncorroded conditions, uniform corrosion simplification and pitting corrosion are discussed. The analytical results reveal the impact of localised pitting corrosion damage on the combined compression-bending performance of CFSTs can be grouped as the stress concentration around corrosion pits, premature local buckling of steel tubes and the reduction in effective confinement. An extended parametric study illustrates that the confinement factor and the mean pit depth have a considerable impact on the combined compression-bending behaviour of CFSTs with localised pitting corrosion. The feasibility of utilising existing design approaches calculates the load-moment interaction diagrams of locally pitted CFSTs following the DoV-based uniform corrosion simplification is evaluated. On this basis, simplified design methods accounting for the characteristic of pitting corrosion are proposed for estimating the post-corrosion load-bearing capacity of CFSTs under combined compression and bending, and reasonable accuracy is achieved.
•An advanced approach is presented for random localised pitting corrosion modelling of steel tubes.•The prediction of stress concentration and nonlinear variation of material confinement is enabled in the modelling.•The effects of localised pitting corrosion on the combined compression-bending performance are comprehensively studied.•Simplified design methods are proposed for predicting the post-corrosion load-bearing capacity.
•Calculation formula of paste thickness on coated aggregate was established.•Calculation model of compressive strength of RBAC was established.•Mix proportion design method of RBAC was established.
...Due to the specific gravity of recycled brick aggregate (RBA) is less than that of natural aggregate (NA), the traditional mix proportion design of concrete can not be used. The purpose of this study is to propose a new mix proportion design method, which is suitable for recycled brick aggregate concrete (RBAC) or lightweight aggregate concrete. In this test, RBA volume fraction, sand volume fraction and water/cement ratio were considered; calculation formula of paste thickness on coated aggregate was established; calculation model of RBAC compressive strength was established, in which RBA volume fraction, the compressive strength of cement mortar and water/cement ratio were considered; mix proportion design method of RBAC based on aggregate skeleton theory was established. The results show that: when the volume fraction of RBA is between 44% and 47%, and the total volume fraction of RBA and sand is about 70%, the compressive strength of RBAC reaches the maximum; when the volume fraction of RBA is between 40% and 50%, the skeleton contribution strength of RBA is greater than that of cement mortar. When sand/cement ratio is about between 0.35 and 2.1, the sand skeleton contribution strength is higher. When the volume fraction of RBA is between 40% and 50%, the actual average paste thickness on coated coarse aggregate (APTCCA) is between 10.04 mm and 5.86 mm and the APTCCA simulated by PFC3D software is between 9.21 mm and 5.75 mm. In the compressive strength calculation model of RBAC, the relative errors of the predicted values are concentrated within 10%, the average relative error is 0.53%, and the correlation coefficient between the predicted values and the test values is 0.96; Compared with ACI 211.2 and ACI 211.6, the mix proportion design method proposed in this paper is to mix more RBA and less sand and cement in concrete mix proportion under the condition of ensuring concrete strength and slump, which is beneficial to protect the environment.
The influence of various Fe contents (5, 10, 20, and 40 wt.%) on the microstructure and properties of powder metallurgy Cu–Fe alloy by spark plasma sintering, subjected to cold rolling and aging ...treatments, was explored. The results showed that, with increasing Fe content from 5 wt.% to 40 wt.%, the distribution of Fe phase evolved from the discrete spheroid to the continuous stagger, accompanying with its size increasing from 0.29 to 1.20 μm. Accordingly, the yield strength of the aged alloy increased from 411.5 to 788.8 MPa, whilst the electrical conductivity decreased from 62.5% (IACS) to 42.0% (IACS). Moreover, a rule of mixture was proposed to calculate the contribution of Cu matrix, primary Fe phase and secondary Fe phase to the yield strength of the alloy, which works well in the prediction of mechanical properties for Cu–Fe alloys with Fe content higher than10 wt.%.
•Effect of fiber reinforcement on bond behavior of FRCAC and GFRP bar was studied.•Adding fibers changed the failure mode and bond hehavior of specimens.•Reinforcing effect on mechanical properties ...was greater than on bond properties.•Basalt and steel fibers showed the most significant improvement in bond properties.•The calculation method of bond strength of FRCAC-GFRP bar was developed.
The increasing construction activities on islands make FRP reinforced coral aggregate concrete (CAC) more and more promising. However, the poor mechanical performance of CAC reduces the bond properties between CAC and GFRP bars, which poses a threat to engineering safety and long-term service. Therefore, fibers were added as reinforcement in CAC to improve the bond properties. In the present study, the effect of fiber reinforcement on the bond behavior between CAC and GFRP bars was studied by pull-out tests. The mechanical properties of fiber reinforced coral aggregate concrete (FRCAC) were also investigated as a comparison to the bond properties. The microstructure and failure characteristics of the interface between FRCAC and GFRP bars were observed through scanning electron microscopy. The results showed that adding fibers as reinforcement can inhibit the development of cracks in FRCAC and even change the failure mode of bonding specimens from concrete splitting to bar pull-out. The mechanical and bond properties of CAC reinforced by fibers were all improved, although the improvement was not as significant as that observed in traditional normal aggregate concrete. The reinforcing effect was more significant on mechanical properties than on bond properties as the fiber content increased. Among polypropylene fiber, basalt fiber, and copper-surfaced steel fiber, basalt fiber and copper-surfaced steel fiber demonstrated a more significant reinforcing effect on the bond properties between FRCAC and GFRP bar than polypropylene fiber. A calculation method for determining the bond strength between FRCAC and GFRP bar was proposed.
•Although there are many studies on fretting wear at present, they are limited to phenomena and mechanisms. Their calculation is very complex and not suitable for engineering design. To solve this ...engineering problem, this article firstly proposes a calculation method for the fretting contact fatigue strength. This method has never been published. There is absolutely no plagiarism in this paper.•The calculation method for the fretting contact fatigue strength has never been published in any international literature. This is the first submission in your journal.•Previously published papers focused on strength failure, but not on micro motion. This time it's about the fretting contact fatigue strength calculation.
Fretting wear and gear contact fatigue belong to adhesive wear. They have similar causes, failure mechanisms, and failure appearance. Drawing inspiration from the gear contact fatigue strength theory, this article creatively proposes a calculation method for the fretting contact fatigue strength. The safety factor of fretting fatigue is calculated to be 0.34. Due to the singularity of the contact point at the edge of the oil groove, the mesh size near this point needs to be sufficiently fine to 0.025 mm. The contact pressure at the edge contact point of the oil groove is calculated by finite element method (FEM) to be 1034 MPa, which is 6.8 times the Lame theoretical value of 152 MPa. The stress concentration is very severe. The fretting contact fatigue strength at the edge of the oil groove is severely insufficient. The friction torque of the interference connection is calculated to be 3.1 times the overload torque of the motor. The fundamental cause of fretting wear is excessive interference and unreasonable design.
The ever-increasing generation of construction and demolition (C&D) waste caused by the frequent occurrence of building fires has posed a threat to environmental protection and waste management over ...the last few decades. The shortage of natural resources provides an impetus for the utilization of C&D waste after fire. Aiming to provide a cleaner option for waste concrete after fire, the viability of using waste concrete after fire as a substitute for coarse aggregate in the production of recycled aggregate concrete (RAC) was investigated and analyzed in detail. The failure mode, stress–strain behavior, mechanical properties and microstructure of the RAC was evaluated with the variation of four different replacement ratios (0%, 25%, 50%, and 100%) and five different treatment temperatures (20 °C, 200 °C, 400 °C, 600 °C, and 800 °C). The experimental results showed despite the failure mode of RAC being similar to that of natural concrete (NC), an increase in the recycled coarse aggregate (RCA) replacement ratio would decrease the slope of curves and strength, and the fcu and fc with 25% replacement ratio for RAC decrease by about 15% and 10% respectively as compared to those for NC. Nevertheless, treatment of elevated temperature for waste concrete can eliminate the damage of replacement ratio to mechanical properties, and the fcu and fc with 25% replacement ratio after 400 °C increased by approximately 12% and 8% respectively as compared with untreated RAC. Against the test result, a series of calculation formulas is proposed to predict the mechanical properties of the RAC whilst a constitutive model is modified with the existing standard to describe the stress–strain behavior of that with the consideration of replacement ratio and treatment temperature. The microstructure analysis indicated that the increase in the RCA replacement ratio would result in the increasing content of adhered mortar characterized by numerous poles and less bond on RCA, whereas treatment of high temperature for waste concrete can decrease the content of adhered mortar on RCA, which makes the microstructure of the RAC more densified.
•Recycled aggregates prepared from waste concrete treated at different temperatures were used for fabricating recycled aggregate concrete.•A series of tests were performed on recycled aggregate concrete under different replacement ratios and treatment temperatures.•The strength calculation model was established by considering the replacement ratio and treatment temperature.•The expressions of stress–strain curves for recycled aggregate concrete were proposed.•Microstructural analysis was conducted to reveal the damage mechanism.
An analysis has been made of the behavior of flange joint components under initial stress loading (pre-clamping) and in service. There have been highlighted the drawbacks in calculating flange joints ...to be found in currently acknowledged methods that do not take into account: - the influence of the bending moment produced by the total hydrostatic end force on bolt strength and flange rotation; - the presence of cracks in the welding or in its thermal influence zone; - the residual stresses; the relaxation of the sealing gasket over time. The calculation method proposed in the paper takes into account all these particularities of loading. Furthermore, alongside the strength calculation of bolts and flanges, a proposal has been put forth for the calculation of the flange joint leak-tightness.
