EXPERIMENTAL STUDY ON CRACK CURVING PROPAGATION IN BENDING BEAMS UNDER IMPULSIVE LOAD

Dynamic fracture behaviour of crack curving in bent beams has been investigated. In order to understand the propagation mechanism of such cracks under impact, an experimental method is used that combines dynamic photoelasticity with dynamic caustics to study the interaction of the flexural waves and the crack. From the state change of the transient stresses in polymer specimen, the curving fracture in the impulsively loaded beams is analyzed. The dynamic responses of crack tips are evaluated by the stress intensity factors for the cracks running in varying curvature paths under bending stress wave.

Experimental study and stress analysis of rock bolt anchorage performance

A new method was developed to apply pull-and-shear loads to the bolt specimen in order to evaluate theanchorage performance of the rebar bolt and the D-Bolt. In the tests, five displacing angles （0°, 20°, 40°,60°, and 90°）, two joint gaps （0 mm and 30 mm）, and three kinds of host rock materials （weak concrete,strong concrete, and concrete-granite） were considered, and stressestrain measurements were conducted.Results show that the ultimate loads of both the D-Bolt and the rebar bolt remained constantwith any displacing angles. The ultimate displacement of the D-Bolt changed from 140 mm at the0 displacing angle （pure pull） to approximately 70 mm at a displacing angle greater than 40. Thedisplacement capacity of the D-Bolt is approximately 3.5 times that of the rebar bolt under pure pull and50% higher than that of the rebar bolt under pure shear. The compressive stress exists at 50 mm from thebolt head, and the maximum bending moment value rises with the increasing displacing angle. The rebarbolt mobilises greater applied load than the D-Bolt when subjected to the maximum bending. Theyielding length （at 0） of the D-Bolt is longer than that of the rebar bolt. The displacement capacity of thebolts increased with the joint gap. The bolt subjected to joint gap effect yields more quickly with greaterbending moment and smaller applied load. The displacement capacities of the D-Bolt and the rebar boltare greater in the weak host rock than that in the hard host rock. In pure shear condition, the ultimateload of the bolts slightly decreases in the hard rock. The yielding speed in the hard rock is higher thanthat in the weak rock. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Microstructural and Microhardness Variation of Amorphous Fe_(78)Si_9B_(13) Alloy during Bend Stress Relaxation

The amorphous Fe78Si9B13 ribbons were bend stress relaxed at various temperature well below the crystallization temperature （Tx） for different time. The effect of pre-annealing on the subsequent bend stress relaxation was examined. The variation of the microstructure and microhardness during bend stress relaxation process was studied using X-ray diffraction （XRD）, atomic force microscopy （AFM） and Vickers microhardness test,respectively. Curvature radius of the amorphous Fe78Si9B13 ribbons decreased with increase bend stress relaxation temperature and time. The microhardness of the stress relaxed specimens increased with time at 300℃ due to the forming of nanocrystals during bend stress relaxation. The pre-annealing reduced the decrease rate of the curvature radius of stress relaxed specimens.

MEASUREMENT OF INTERNAL STRESSES OF METAL MULTILAYER COMPOSITE COATINGS

The principle, formula and determination of internal stresses of metal multilayer composite coatings by means of the bending strip method were studied. Using this method, internal stresses of ion-plated metal multilayer composite coatings and thick monolayer coating of aluminium bronze, stainless steel and nickel-iron alloy were determined. The reason of decrement in internal stresses of multilayer composite coatings was discussed.

Vortex-Induced Vibrations of A Free-Spanning Pipe Based on A Nonlinear Hysteretic Soil Model at the Shoulders

The pipe-soil interactions at shoulders can significantly affect the vortex-induced vibrations (VIV) of free-spanning pipes in the subsea. In this paper, the seabed soil reacting force on the pipe is directly calculated with a nonlinear hysteretic soil model. For the VIV in the middle span, a classic van der Pol wake oscillator is adopted. Based on the Euler-Bernoulli beam theory, the vibration equations of the pipe are obtained which are different in the middle span and at the two end shoulders. The static configuration of the pipe is firstly calculated and then the VIV is simulated.The present model is validated with the comparisons of VIV experiment, pipe-soil interaction experiment and the simulation results of VIV of free-spanning pipes in which the seabed soil is modelled with spring-dashpots. With the present model, the influence of seabed soil on the VIV of a free-spanning pipe is analyzed. The parametric studies show that when the seabed soil has a larger suction area, the pipe vibrates with smaller bending stresses and is safer.While with the increase of the shear strength of the seabed soil, the bending stresses increase and the pipe faces more danger.

Bending properties of green forage maize in field

Stalk lodging is prone to occur during the harvesting of green forage maize due to the header and root anchorage,resulting in loss of harvest.In particular,the fallen stalk wraps around the header,causing a blockage and increasing the energy cost.To address this problem,the deflection model was analyzed and established and a novel method to explore the field bend characteristics of green forage maize was proposed.The effects of stalk diameter,bending angle,and cutting height on bending stress and Young’s modulus were explored by using the method of in-situ measurement.Additionally,the bending deflection,axial displacement and measuring point displacement were obtained.Experimental results indicate that the stalk diameter and bending angle have a significant influence on bending stress.The bending stress has a positive correlation with bending angle and cutting height,while there is a negative correlation with stalk diameter.On the other hand,the bending angle,stalk diameter,and cutting height are closely related to the Young’s modulus.The mean values of the Young’s modulus decrease as a quadratic function with the increasing diameter and bending angle,while the cutting height has the opposite effect on it.Besides,the average values of bending deflection,axial displacement,and measuring point displacement exhibit an increasing trend when the bending angle and cutting height increase.This study results can provide a reference for studying the failure mechanism of green forage maize stalk harvesting,and the design of green forage maize harvesting machinery.

Stress and Springback Analyses of API X70 Pipeline Steel Under 3-Roller Bending via Finite Element Method

3-Roller bending is a widely applied manufacturing process, particularly in structural steel pipe industry.However, due to the difficulty and high cost of measuring stress distribution inside sheet material via traditional method,internal stress/strain response during forming is largely unexplored. The focuses of this study are two：（1） to map the radii of curvature as well as the stress inside the work piece during forming by utilizing the meshing mechanism of finite element method, and（2） to further provide some numeric guidelines for the configuration of the rolling system in order to improve production efficiency and product quality. The results of this study indicate that：（1） it is crucial to properly choose forming parameter in order to produce product with desired radii;（2） much like a gradual springback process, the radii of curvature gradually increase from the top roller to the exit-side bottom roller;（3） under the assumptions made in this study, to produce pipes with a specified diameter with varying configurations of the 3-roller system will not significantly change the final residual stress; and（4） finally, shifting of the neutral axis up to 2.0% of the thickness toward the compressing side during the forming process is observed.

CURVED OPEN CHANNEL FLOW ON VEGETATION ROUGHENED INNER BANK

A RNG numerical model together with a laboratory measurement with Micro ADV are adopted to investigate the flow through a 180o curved open channel（a 4 m straight inflow section,a 180o curved section,and a 4m straight outflow section）partially covered with rigid vegetations on its inner bank.Under the combined action of the vegetation and the bend flow,the flow structure is complex.The stream-wise velocities in the vegetation region are much smaller than those in the non-vegetation region due to the retardation caused by the vegetation.For the same reason,no clear circulation is found in the vegetated region,while in the non-vegetation region,a slight counter-rotating circulation is found near the outer bank at both 90o and downstream curved cross-sections.A comparison between the numerical prediction and the laboratory measurement shows that the RNG model can well predict the flow structure of the bend flow with vegetation.Furthermore,the shear stress is analyzed based on the numerical prediction.The much smaller value in the inner vegetated region indicates that the vegetation can effectively protect the river bank from scouring and erosion,in other words,the sediment is more likely to be deposited in the vegetation region.