Assessment of cyclic deformation and critical stress amplitude of jointed rocks via cyclic triaxial testing

Jointed rock specimens with a natural replicated joint surface oriented at a mean dip angle of 60were prepared,and a series of cyclic triaxial tests was performed at different confining pressures and cyclic deviatoric stress amplitudes.The samples were subjected to 10,000 loading-unloading cycles with a frequency of 8 Hz.At each level of confining pressure,the applied cyclic deviatoric stress amplitude was increased incrementally until excessive deformation of the jointed rock specimen was observed.Analysis of the test results indicated that there existed a critical cyclic deviatoric stress amplitude(i.e.critical dynamic deviatoric stress)beyond which the jointed rock specimens yielded.The measured critical dynamic deviatoric stress was less than the corresponding static deviatoric stress.At cyclic deviatoric stress amplitudes less than the critical dynamic deviatoric stress,minor cumulative residual axial strains were observed,resulting in hysteretic damping.However,for cyclic deviatoric stresses beyond the critical dynamic deviatoric stress,the plastic strains increased promptly,and the resilient moduli degraded rapidly during the initial loading cycles.Cyclic triaxial test results showed that at higher confining pressures,the ultimate residual axial strain attained by the jointed rock specimen decreased,the steadystate dissipated energy density and steady-state damping ratio per load cycle decreased,while steadystate resilient moduli increased.

Research on Complexity of Surface Undulating Shapes of Rock Joints

The surface undulating shapes of rock joints have been described qualitatively or experimental quantitatively for a long time. The non determined describing method can not fit quantitative evaluation of mechanical parameters of rock joints in engineering. In this paper, relative amplitude ( R A) is chosen as a quantitative describing index of surface measurement of 1 023 surface undulating curves which conducted by profile curve device(PCD). We discuss the nonuniformity,anisotropy and unhomogeneity of surface undulating shapes of joints. A new method that analyzes the complexity of surface undulating shapes of rock joints directional statistically in various rock joints is also put forward.

Finite element simulation for mechanical response of surface mounted solder joints under different temperature cycling

Nonlinear finite element simulation for mechanical response of surface mounted solder joint under different temperature cycling was carried out. Seven sets of parameters were used in order to evaluate the influence of temperature cycling profile parameters. The results show that temperature cycling history has significant effect on the stress response of the solder joint. Based on the concept of relative damage stress proposed by the authors, it is found that enough high temperature holding time is necessary for designing the temperature cycling profile in accelerated thermal fatigue test.

NORMAL CONTACT STIFFNESS OF THE ELLIPTIC AREA BETWEEN TWO ASPERITIES

A new expression for contact deformation is given, and the normal contact stiff- ness between single asperities is derived according to Hooke＇s law. A contact model between two ellipsoidal asperities is simulated by the FE method, the result compared with the theoretical solution. It is found that the curves of the normal contact stiffness versus the included angle in the principal curvature direction show similar trends and evolve as a cosine feature. The effects of the parameters on normal contact stiffness are found to show that normal contact stiffness increases and reaches the upper limit gradually with an increase in these parameters.

A Modified Elastoplastic Contact Stiffness Model Considering Continuous Smooth Contact Characteristics and Substrate Deformation

The contact stiffness of the joint surface directly affects the static and dynamic mechanical behavior,and accuracy of the machine tool.A new elastoplastic contact stiffness model is proposed by considering continuous and smooth contact characteristics and substrate deformation.First,the interpolation interval of cubic Hermite polynomials is improved to meet the continuous and smooth change of contact parameters during asperity deformation.Then,the micro-contact mechanism considering substrate deformation is explored by establishing an asperity-substrate system model.Furthermore,combined with statistical principles,a new contact stiffness model of the joint surface is established.Finally,the correctness of the built model is verified by comparing with experimental data and different contact models.The simulation results show that the model changes continuously and smoothly in the three deformation regions.The substrate deformation mainly affects the asperities in the elastic contact stage.The smoother is the surface,the more significant is the influence of substrate deformation.

3D-Printed Guide Plate Assisted Osteochondral Transplantation for the Treatment of Large Talar Defect:Case Report and Literature Analysis

Osteochondral lesion of the talus(OLT)is a common cause of ankle pain that often occurs in the talar dome and leads to talar cartilage and subchondral bone damage.Osteochondral autograft transplantation is a logical treatment option.It is known that if the cartilage does not heal properly after injury,it degenerates,and osteoarthritis worsens.A three dimensional(3D)-printed guide plate can be used to find the curved articular surface from the donor site which optimally fits the defect in the talus.Herein,we present the case of a 28-year-old man who had an open injury from the crash of a tricycle in the right ankle at the age of 5.Radiographs revealed a large defect in the medial talar dome that affected nearly half of the talar dome.We performed the debridement of the ankle lesion.An osteochondral autograft was harvested from the medial femoral condyle(MFC)with the help of a personalised 3D-printed guide plate.This 3D-printed guide plate simulated the contour of a specific area in the talar dome,which involved the site of the defect.The autograft was then transplanted into the talus defect.The efficacy of this technique was evaluated at 2,4,and 7 months after surgery and proven to be reliable.