Comparison study on calculation methods of bending behavior of Chinese reinforced concrete beams from 1912 to 1949

In order to study the calculation methods of bending behavior of Chinese reinforced concrete beams from 1912 to 1949, tests on the mechanical performance of 66 rebars from different modem Chinese concrete buildings, the concrete compressive strength of 12 modem Chinese concrete buildings, and the concrete cover thickness of 9 modem Chinese concrete buildings are carried out; and the actual material properties and structural conformations of modem Chinese concrete buildings are obtained. Then, the comparison on calculation methods of bending behavior including the original Chinese calculation method, the present Chinese calculation method, the present American calculation method and the present European calculation method is studied. The results show that the original Chinese calculation method of bending behavior is based on the allowable stress calculation method, and the design safety factors are 3.55 to 4. 0. In term of the calculation area of longitudinal rebars of reinforced concrete beams, without considering earthquake action, the original Chinese structural calculation method is safer than the present Chinese structural calculation method, the present European structural calculation method, and the present American structural calculation method. The results can provide support for the structural safety assessments of modem Chinese reinforced concrete buildings.

Molecular dynamics analysis on bending mechanical behavior of alumina nanowires at different loading rates

The molecular dynamics(MD)model ofα-Al_(2)O_(3) nanowires in bending is established by using LAMMPS to calculate the atomic stress and strain at different loading rates in order to study the effect of loading rate on the bending mechanical behaviors of theα-Al_(2)O_(3) nanowires.Research results show that the maximum surface stress−rotation angle curves ofα-Al_(2)O_(3) nanowires at different loading rates are all divided into three stages of elastic deformation,plastic deformation and failure,where the elastic limit point can be determined by the curve symmetry during loading and unloading cycle.The loading rate has great influence on the plastic deformation but little on the elastic modulus ofα-Al_(2)O_(3) nanowires.When the loading rate is increased,the plastic deformation stage is shortened and the material is easier to fail in brittle fracture.Therefore,the elastic limit and the strength limit(determined by the direct and indirect MD simulation methods)are closer to each other.The MD simulation result ofα-Al_(2)O_(3) nanowires is verified to be valid by the good agreement with the improved loop test results.The direct MD method becomes an effective way to determine the elastic limit and the strength limit of nanoscale whiskers failed in brittle or ductile fracture at arbitrary loading rate.

Shape Memory Polymer Composite Booms with Applications in Reel-Type Solar Arrays

Solar arrays are the primary energy source for spacecraft.Although traditional rigid solar arrays improve power supply,the quality increases proportionally.Hence,it is difficult to satisfy the requirements of high-power and low-cost space applications.In this study,a shape-memory polymer composite(SMPC)boom was designed,fabricated,and characterized for flexible reel-type solar arrays.The SMPC boom was fabricated from a smart material,a shape-memory polymer composite,whose mechanical properties were tested.Additionally,a mathematical model of the bending stiffness of the SMPC boom was developed,and the bending and buckling behaviors of the boom were further analyzed using the ABAQUS software.An SMPC boom was fabricated to demonstrate its shape memory characteristics,and the driving force of the booms with varying geometric parameters was investigated.We also designed and manufactured a reel-type solar array based on an SMPC boom and verified its self-deployment capability.The results indicated that the SMPC boom can be used as a deployable unit to roll out flexible solar arrays.

Effect of extrusion ratio on the microstructure and texture evolution of AZ31 magnesium alloy by the staggered extrusion(SE)

There are many problems with the conventional processes of magnesium alloy bending products,such as long processes and difficulty in controlling the product shape.This paper provides a staggered extrusion(SE)process to solve the above manufacturing bottlenecks.The effects of different extrusion ratios(λ)on the AZ31 magnesium alloy bending products prepared by the SE process was investigated in this paper.The results show that the bending radii of the AZ31 Mg bending products increase with the increase ofλat the same staggered distance(h=16 mm).When A is in creased from 11.11 to 44.44,the average bending radius of bending products is decreased from 14.7 mm to 9 mm,and the average grain size is decreased by 59.43%.After the SE process,the extruded fiber texture of the AZ31 Mg bending products is obvious,and the deformed texture is a mixed texture of{0001}(10-10)deformation texture and{10-11}(11-20)recrystallization texture.The results of XRD and EBSD showed that pyramidal slip is an important mode of crystal slip systems in AZ31 magnesium alloys during the SE process.It provided a scientific basis for forming AZ31 Mg alloy bending products with excellent microstructure by the SE process.

A simplified method for investigating the bending behavior of piles supporting embankments on soft ground

In recent years,concrete and reinforced concrete piles have been widely used to stabilize soft ground under embankments.Previous research has shown that bending failure,particularly during rapid filling on soft ground,is the critical failure mode for pile-supported embankments.Here,we propose an efficient two-stage method that combines a test-verified soil deformation mechanism and Poulos’solution for pile–soil interaction to investigate the bending behavior of piles supporting embankments on soft ground.The results reveal that there are three possible bending failure scenarios for such piles:at the interface between the soft and firm ground layers,at mid-depths of the fan zone,and at the boundary of the soil deformation mechanism.The location of the bending failure depends on the position and relative stiffness of the given pile.Furthermore,the effect of embedding a pile into a firm ground layer on the bending behavior was investigated.When the embedded length of a pile exceeded a critical value,the bending moment at the interface between the soft and firm ground layers reached a limiting value.In addition,floating piles that are not embedded exhibit an overturning pattern of movement in the soft ground layer,and a potential failure is located in the upper part of these piles.

Experimental and numerical investigation of mechanical behavior of plain woven CFRP composites subjected to three-point bending

The mechanical behavior of plain woven Carbon Fiber-Reinforced Polymer(CFRP)composites under Three-Point Bending(TPB)is investigated via experimental and numerical approaches.Multiscale models,including microscale,mesoscale and macroscale models,have been developed to characterize the TPB strength and damages.Thereinto,Representative Volume Elements(RVEs)of the microscale and mesoscale structures are established to determine the effective properties of carbon-fiber yarn and CFRP composites,respectively.Aimed at accurately and efficiently predicting the TPB behavior,an Equivalent Cross-Ply Laminate(ECPL)cell is proposed to simplify the inherent woven architecture,and the effective properties of the subcell are computed using a local homogenization approach.The macroscale model of the TPB specimen is constructed by a topology structure of ECPL cells to predict the mechanical behavior.The TPB experiments have been performed to validate the multiscale models.Both the experimental and numerical results reveal that delamination mainly appears in the top and bottom interfaces of the CFRP laminates.And matrix cracking and delamination are identified as the significant damage modes during the TPB process.Finally,the quasi-static and dynamic behaviors of plain woven composites are discussed by comparing the results of Low-Velocity Impact(LVI)and TPB simulations.

Deformation behavior of laser bending of circular sheet metal

The application of a thermal source in non-contact forming of sheet metal has long been used. However, the replacement of this thermal source with a laser beam promises much greater controllability of the process. This yields a process with strong potential for application in aerospace, shipbuilding, automobile, and manufacturing industries, as well as the rapid manufacturing of prototypes and adjustment of misaligned components. Forming is made possible through laser-induced non-uniform thermal stresses. In this letter, we use the geometrical transition from rectangular to circle-shaped specimen and ring-shaped specimen to observe the effect of geometry on deformation in laser forming. We conduct a series of experiments on a wide range of specimen geometries. The reasons for this behavior are also analyzed. Experimental results are compared with simulated values using the software ABAQUS. The utilization of line energy is found to be higher in the case of laser forming along linear irradiation than along curved ones. We also analyze the effect of strain hindrance. The findings of the study may be useful for the inverse problem, which involves acquiring the process parameters for a known target shape of a wide range of complex shape geometries.

Mechanical Properties and Fracture Behavior of Mg-Al/AlN Composites with Different Particle Contents

In this study, magnesium matrix composites reinforced with different loading of AlN particles were fabricated by the powder metallurgy technique. The microstructure, bending strength and fracture behavior of the resulting Mg-Al/Al N composites were investigated. It showed that the 5 wt% AlN reinforcements led to the highest densification and bending strength. The total strengthening effect of AlN particles was predicted by considering the contributions of CTE mismatch between the matrix and the particles,load bearing and Hall-Petch mechanism. The results revealed that the increase of dislocation density,the change of Mg17Al12 phase morphology, and the effective load transfer were the major strengthening contributors to the composites. The fracture of the composites altered from plastic to brittle mode with increasing reinforcement content. The regions of clustered particles in the composites were easy to be damaged under external load, and the fracture occurred mainly along grain boundaries.