Effects of Plastic Deformation and Stresses on Dilatation duringthe Martensitic Transformation in a B-bearing Steel

To provide data for improved modelling of the behaviour of steel components in a simultaneous forming and quenching process, the effects of plastic deformation and stresses on dilatation during the martensitic transformation in a B-bearing steel were investigated. It was found that plastic deformation of austenite at high temperatures enhances ferrite formation significantly, and consequently, the dilatation decreases markedly even at a cooling rate of 280'C/s. The created ferritic-martensitic microstructure possesses clearly lower hardness and strength than the martensitic structure. Elastic stresses cause the preferred orientation in martensite to be formed so that diametric dilatation can increase by nearly 200% under axial compression.

Follow-up study on symptom distress in esophageal cancer patients undergoing repeated dilation

BACKGROUND Repeated endoscopic probe dilatation is the most preferred treatment for esophageal stenosis which may cause high levels of symptom distress in the patient’s home rehabilitation stage.AIM To explore the changes in the symptom distress level and its correlation with the dilation effect in patients with esophageal carcinoma undergoing repeated dilations for lumen stenosis.METHODS The difference(R2-R1)between the diameter of the esophageal stenosis opening(R1)of the patients before dilation(R1)and after dilation(R2)was calculated to describe the extent and expansion of the esophageal stenosis before and after dilation.The M.D.Anderson Symptom Inventory was used to describe the symptom distress level of patients with dilation intermittence during their stay at home and to explore the correlation between the dilation effect and symptom distress level.RESULTS The diameter of the esophagus(R1)increased before each dilation in patients undergoing esophageal dilation(P<0.05).The diameter(R2)increased after dilation(P<0.05);the dilation effect(R2-R1)decreased with the number of dilations(P<0.05).The total symptom distress score significantly increased with the number of dilations(P<0.05).The symptom distress scores of the patients were negatively correlated(P<0.05)with the previous dilation effect(R2-R1)and the esophageal diameter(R2)after the previous dilation.After the 1 st to 4 th dilations,the patient’s symptom distress score was negatively correlated with the esophageal diameter(R12)before the next dilation,while there was no significant correlation(P>0.05)with the other dilations.CONCLUSION In patients who have undergone repeated dilations,better effect stands for lower symptom distress level and the increase in symptom distress has a prompt effect on the severity of the next occurrence of restenosis.

Shear strength criteria for rock,rock joints,rockfill and rock masses:Problems and some solutions

Although many intact rock types can be very strong,a critical confining pressure can eventually be reached in triaxial testing,such that the Mohr shear strength envelope becomes horizontal.This critical state has recently been better defined,and correct curvature or correct deviation from linear Mohr-Coulomb（MC） has finally been found.Standard shear testing procedures for rock joints,using multiple testing of the same sample,in case of insufficient samples,can be shown to exaggerate apparent cohesion.Even rough joints do not have any cohesion,but instead have very high friction angles at low stress,due to strong dilation.Rock masses,implying problems of large-scale interaction with engineering structures,may have both cohesive and frictional strength components.However,it is not correct to add these,following linear M-C or nonlinear Hoek-Brown（H-B） standard routines.Cohesion is broken at small strain,while friction is mobilized at larger strain and remains to the end of the shear deformation.The criterion ＇c then σn tan φ＇ should replace ＇c plus σn tan φ＇ for improved fit to reality.Transformation of principal stresses to a shear plane seems to ignore mobilized dilation,and caused great experimental difficulties until understood.There seems to be plenty of room for continued research,so that errors of judgement of the last 50 years can be corrected.

Hardening-Softening Constitutive Model of Hard Brittle Rocks Considering Dilatant Effects and Safety Evaluation Index

The damage and even failure of hard brittle rocks has been the most important challenge facing the safety of construction of deep engineering works,so the key to solving this problem is the recognition of the strength characteristics and description of the mechanical behavior of hard brittle rocks.Therefore,in view of this problem,in this study,we first analyzed the strength and mechanical response characteristics revealed in tests of,and site excavation in,hard brittle rocks.Second,by analyzing rock-strength envelopes on meridional and deviatoric planes,the generalized polyaxial strain energy(GPSE)strength criterion was applied.This allows description of the effects of the minimum principal stress,intermediate principal stress,hydrostatic pressure,and Lode’s angle of stress on the strength of hard rocks.By establishing evolutionary relationships of strength parameters and dilation parameters with plastic volumetric strain in rock failure,we established an elasto-plastic mechanical constitutive model for hard brittle rocks based on the GPSE criterion.In addition,through use of the failure approach index theory and the dilatancy safety factor,an evaluation index for degree of damage considering dilatant effects of rocks was proposed.Finally,the constitutive model established in this study and the proposed evaluation index were integrated into the numerical simulation method to simulate triaxial tests on rocks and numerical simulation of deformation and fracture of the rocks surrounding the deep-buried auxiliary tunnels in China’s Jinping II Hydropower Station.In this way,the reasonableness of the model and the index was verified.The strength theory and the constitutive model established in this research are applicable to the analysis of high-stress deformation and fracture of hard brittle rock masses,which supports the theoretical work related to deep engineering operations.