高强钢焊接区“三点弯曲”试验拘束应力的测定

采用“三点弯曲”试验对HQ13 0高强钢焊接熔合区附近的应力状态进行了试验测定。试验结果表明 ,外加载荷增大 ,焊接试样的应力应变值逐渐增大 ,经过近似直线的弹性范围后 ,达到塑变区后应变发生突变。外加载荷增加使产生裂纹的可能性增大。尽管应变的公式计算值和实测值之间存在着一定的偏差 ,但二者的总体趋势是一致的 ,在要求不太严格或只要求获得应力变化规律的情况下 ,仍可用公式法估算。

Influence factors on stress corrosion cracking of P 110 tubing steel under CO2 injection well annulus environment

Stress corrosion cracking （SCC） behavior of P 110 tubing steel in simulated C02 injection well annulus environments was investigated through three-point bent tests, potentiodynamic polarization and EIS measurements. The results demonstrate that SCC of P110 tubing steel could occur in acidulous simulated environment, and the sensitivity of SCC increases with the decrease ofpH, as well as increase of sulfide concentration and total environmental pressure. Both anodic dissolution and hydrogen embrittlement make contributions to the SCC. Adequate concentration of corrosion inhibitor can inhibit the occurrence of SCC on account of the inhibition of localized anodic dissolution and cathodic hydrogen evolution.

Processing and properties of 2D SiC/SiC composites by precursor infiltration and pyrolysis

Two-dimensional plain-weave silicon carbide fiber fabric reinforced silicon carbide(2D-SiC/SiC)composites were molded by stacking method and densified through precursor infiltration and pyrolysis(PIP)process.SiC coating was deposited as the fiber/matrix interphase layer by chemical vapor deposition(CVD)technique.Fiber/matrix debonding and relatively long fiber pullouts were observed on the fracture surfaces.Additionally,the flexural strength and elastic modulus of the composites with and without fiber/matrix interphase layer were investigated using three-point bending test and single-edge notched beam test.The results show that the fiber fraction and the porosity of 2D-SiC/SiC composites with and without coating are 27.2%(volume fraction)and 11.1%,and 40.7%(volume fraction)and 7.5%,respectively.And the flexural strength and elastic modulus of 2D-SiC/SiC composites with and without coating are 363.3 MPa and 127.8 GPa,and 180.2 MPa and 97.2 GPa,respectively.With a proper thickness,the coating can effectively adjust the fiber/matrix interface,thus causing a dramatic increase in the mechanical properties of the composites.

Potential of acoustic emissions from three point bending tests as rock failure precursors

Development of failure in brittle materials is associated with microcracks,which release energy in the form of elastic waves called acoustic emissions. This paper presents results from acoustic emission measurements obtained during three point bending tests on Nestos marble under laboratory conditions.Acoustic emission activity was monitored using piezoelectric acoustic emission sensors,and the potential for accurate prediction of rock damage based on acoustic emission data was investigated. Damage localization was determined based on acoustic emissions generated from the critically stressed region as scattered events at stresses below and close to the strength of the material.

Flexural response of reinforced concrete beams strengthened with post-poured ultra high toughness cementitious composites layer

Four-point bending tests were conducted up to failure on eleven reinforced concrete (RC) beams and strengthening beams to study the effectiveness of externally pouring ultra high toughness cementitious composites (UHTCC) on improving the flexural behavior of existing RC beams.The strengthening materials included UHTCC and high strength grade concrete.The parameters,such as thickness and length of strengthening layer and reinforcement in post-poured layer,were analyzed.The flexural behavior,failure mode and crack propagation of composite beams were investigated.The test results show that the strengthening layer improves the cracking and ultimate load by increasing the cross section area.Introducing UHTCC material into strengthening not only improves the bearing capacity of the original specimens,but also disperses larger cracks in upper concrete into multiple tightly-spaced fine cracks,thus prolonging the appearance of harm surface cracks and increasing the durability of existing structures.Compared with post-poured concrete,UHTCC is more suitable for working together with reinforcement.The load?deflection plots obtained from three-dimensional finite-element model (FEM) analyses are compared with those obtained from the experimental results,and show close correlation.

Experimental Investigation on Springback Performance of Transformation-induced Plasticity Steel Sheet during Cyclic Bending Process

In order to investigate the springback performance of a cold-rolled transformation-induced plasticity （TRIP） steel sheet during cyclic bending, three-points bending experiments were performed. The specimen was firstly forward bended and then reversed bended according to three basic punch strokes, 10 mm, 20 mm and 30 mm, respectively. The outlines of the deformed specimens, punch load and crosshead displacement were obtained. The experimental procedures and the method of determining the springback displacement were reported in detail. The contributi^m of the strain hardening and decrease of elastic modulus to the overall springback was explained. The results demonstrated that springback increases both with the cycles and with the punch stroke during the cyclic bending process. Furthermore, springback in forward bending is larger than that in the corresponding reverse bending. This may be helpful to understand the complex springback behavior of the complicated sheet metal pancls.

Micromechanical characteristics of the asphalt mixture in bending condition

The characteristics of asphalt mixtures are associated with the key features of the mixed material when it is not damaged.Two-dimensional(2D) microstructure images of asphalt mixture bending beam specimen were captured by a CCD camera.After image processing,such as noise elimination,boundary identification,image binarization and vectorization,the images were imported into finite element(FE) software in order to set up the micromechanical finite element(FE) model.The simulation results show that the displacement contours spectrum is not a smooth curve since the mixed material is heterogeneous.Also,the largest strain value exists at the bottom of the specimen between two coarse aggregates,and it is the point where the fracture starts.The stress values of aggregates are larger than those of the asphalt matrix.Different from the strain of asphalt matrix,the strain of aggregates is close to zero because the aggregates have higher capability to resist self-deformation.The difference in deformation between aggregate and asphalt matrix can lead to an interface crack as a final result.All these results can be improved by three-point bending test of asphalt mixture beam.

Interface contact profiles of a novel locking plate and its effect on fracture healing in goat

Objective： To evaluate the interface characteristics of the new-designed locking plate （LP） and limited contact-dynamic compression plate （LC-DCP） and compare the fracture healing between LP and LC-DCP in a goat tibia fracture model. Methods： Eight-hole LP and LC-DCP were applied to fix fresh goat tibiae in a reproducible manner. The average pressure, force and interface contact area were calculated using Fuji prescale pressure sensitive film interposed among the plate and the bone and image analysis system, Eighthole LP and LC-DCP were applied to each tibia in a goat tibia fracture model. The fracture healing was evaluated by X-ray photography at postoperative 8 weeks. The goats were sacrificed at postoperative 12 weeks. Three-point bending test was conducted in the tibiae. Results： The interface contact of LP system was smaller than that ofLC-DCP （P〈0.05）, while interface contact force of LP system was higher than that of LC-DCP （P〈0.05）. Radiographs revealed that the fracture line disappeared in the LP group, while the fracture line was visible in DCP group at postoperative 8 weeks. At postoperative 12 weeks, the bending strength and bending load of fractured tibia were higher in LP group than in DCP group, respectively.