Experimental study on the shear performance of quasi-NPR steel bolted rock joints

Quasi-NPR(negative Poisson’s ratio)steel is a new type of super bolt material with high strength,high ductility,and a micro-negative Poisson’s effect.This material overcomes the contrasting characteristics of the high strength and high ductility of steel and it has significant energy-absorbing characteristics,which is of high value in deep rock and soil support engineering.However,research on the shear resistance of quasi-NPR steel has not been carried out.To study the shear performance of quasi-NPR steel bolted rock joints,indoor shear tests of bolted rock joints under different normal stress conditions were carried out.Q235 steel and#45 steel,two representative ordinary bolt steels,were set up as a control group for comparative tests to compare and analyze the shear strength,deformation and instability mode,shear energy absorption characteristics,and bolting contribution of different types of bolts.The results show that the jointed rock masses without bolt reinforcement undergo brittle failure under shear load,while the bolted jointed rock masses show obvious ductile failure characteristics.The shear deformation ca-pacity of quasi-NPR steel is more than 3.5 times that of Q235 steel and#45 steel.No fracture occurs in the quasi-NPR steel during large shear deformation and it can provide stable shear resistance.However,the other two types of control bolts become fractured under the same conditions.Quasi-NPR steel has significant energy-absorbing characteristics under shear load and has obvious advantages in terms of absorbing the energy released by shear deformation of jointed rock masses as compared with ordinary steel.In particular,the shear force plays a major role in resisting the shear deformation of Q235 steel and#45 steel,therefore,fracture failure occurs under small bolt deformation.However,the axial force of quasi-NPR steel can be fully exerted when resisting joint shear deformation;the steel itself does not break when large shear deformation occurs,and the supporting effect of the jointed rock mass is effectively guaranteed.

Two-stage revision in periprosthetic knee joint infections

Periprosthetic joint infection(PJI)following total knee arthroplasty is one of the most catastrophic and costly complications that carries significant patient wellness as well as economic burdens.The road to efficiently diagnosing and treating PJI is challenging,as there is still no gold standard method to reach the diagnosis as early as desired.There are also international controversies with respect to the best approach to manage PJI cases.In this review,we highlight recent advances in managing PJI following knee arthroplasty surgery and discuss in depth the two-stage revision method.

Shear behavior of two-order morphology in rock joints

Two-order morphology of rock joints named as waviness and unevenness can be separated by morphology classification method,which plays a decisive role in the evolution of shear stress during the shear test.The joint morphology is obtained by using 3D printing and 3D laser scanning techniques and the joint model samples in two-order morphology are produced by cement mortar.Then,shear tests are performed under different normal loads.Results shows that the waviness is dominant in the total morphology during the shear test,and the shear contribution of unevenness mainly occurs in the climbing phase of shearing process.Comparing the failure modes of two-order morphology,waviness mainly embodies shear dilation characteristics and unevenness mainly shows shear wear characteristics.Based on this,a quantitative parameter is proposed to represent the ratio of the peak shear strength of the two-order morphology to that of total morphology.The functional relationship between the peak shear strength of total and two-order morphologies is determined,providing a theoretical method for further in-depth study on the shear strength of the interaction with two-order morphology of rock joints.

联合GNSS与GRACE/GRACE-FO数据反演中国西南地区陆地水储量变化

GNSS和重力恢复与气候试验(GRACE)及其后续任务(GRACE-FO)给陆地水储量变化(TWSC)研究带来了技术革新,但这两种技术估计的区域TWSC具有不同的时空尺度和精度特性。因此,有必要融合两种观测数据,以获得同一尺度且高精度的TWSC。本文基于GNSS独立反演模型,使用求和算子对喷气推进实验室(JPL)的GRACE/GRACE-FO Mascon数据进行求和运算来构建约束,通过赤池贝叶斯准则选择最优模型参数,构建了一种联合GNSS与GRACE/GRACE-FO数据的区域TWSC反演模型。随后,本文设计数值模拟试验,以验证利用该模型反演中国西南地区TWSC的可行性。结果显示,1000次试验中联合反演估算的均方根误差均值为10 mm,比GNSS独立反演结果低47%。基于此方法,本文联合GNSS与JPL Mascon数据反演了中国西南地区2011年1月—2022年6月的时变TWSC。对比联合反演、GNSS独立反演、GRACE/GRACE-FO和高分辨率全球陆地数据同化系统(GLDAS)的结果,发现联合反演与GLDAS的TWSC周年振幅空间分布特征最吻合,表明联合反演估计的TWSC空间分辨率优于GNSS独立反演和GRACE的结果。最后,结合水平衡方程估算的区域水文收支情况,并通过广义三角帽方法评估陆地水储量等效水柱高的变化率(d(EWH)/d t)的不确定性。结果显示,联合反演估计的d(EWH)/d t不确定性为8 mm/月,较GRACE/GRACE-FO、GNSS独立反演和水平衡方程结果分别低33%、68%和62%。研究结果表明,与GNSS和GRACE/GRACE-FO独立反演方法相比,联合反演能够改善TWSC估值的精度,可为水资源管理决策及水文气候学研究提供更可靠的数据支撑。

基于T-S模糊建模的气动肌肉拮抗关节预测角度控制

目的:为了提升气动肌肉拮抗关节的控制精度。方法:提出了一种用于气动肌肉拮抗关节角度跟踪的T-S模糊模型预测控制方法。建立了拮抗关节的T-S模糊模型,并对模型进行了离散化处理;基于离散后的T-S模糊模型,设计了拮抗关节的模型预测控制器,通过特征值法验证了系统的稳定性。结果:仿真实验表明,T-S模糊模型预测控制器跟踪±15°和±10°的角度时,相对于传统模型预测控制,平均绝对误差分别降低了29.05%和44.11%。结论:设计的T-S模糊模型预测控制器提高了气动肌肉拮抗关节的控制精度。

Design and Analysis of Tapered Stress Joint for Top Tensioned Riser System

Stress Joint （SJ） plays a key role in the Top Tensioned Riser （TTR） system for deep water engineering. A preliminary design method of tapered SJ is proposed in the paper, which could help designers obtain accurate design data. After a further sensitive analysis is carried out, the related parameters choice and control methods are recommended in the engineering practice. By taking the extreme environment conditions into consideration, the effects of bending stress reduction and curve control are analyzed, and the 3-D FE models are established by ABQOUS for numerical evaluation to verify the correctness of design results. At last, dynamic analysis and fatigue analysis, based on actual project, are carried out with designed stress joint. The analysis results prove the feasibility and guidance of this method in the practical engineering applications.

Bennett's fracture associated with fracture of Trapezium——A rare injury of first carpo-metacarpal joint

Association of fracture of trapezium with Bennett'sfracture is very rare and makes reduction and stabilisation more difficult. We are reporting a rare case of Bennett's fracture with fracture of the trapezium and subluxation of the carpo-metacarpal joint(CMC) joint. The patient was a 47-year-old school teacher who fell from his motorbike on his outstretched right dominant hand. Radiographs and computed tomography showed fracture of the trapezium with subluxation of the CMC joint, associated with Bennett's fracture. Open reduction and internal fixation was carried out. Trapezium was reduced first and secured with a 2 mm diameter screw. Bennett's fracture was then reduced and fixed with two per-cutaneously placed Kirchner's wires. CMC was stabilised with percutaneous Kirchner's wires. Latest follow up at 12 mo showed a healed fracture with good reduction of the CMC joint. Clinically patient had no pain and normal extension, abduction and opposition of the thumb. QuickD ASH score was 3.9/100. Thus, fracture of trapezium associated with a Bennett's fracture is a rare injury and if ignored it may lead to poor results. This injury is more challenging to manage than an isolated Bennett's fracture as anatomical reduction of the trapezium with reduction of the first CMC is needed. Fracture of the trapezium should be fixed first as this will provide a stable base for reduction of the Bennett's fracture.

Basic Characteristics of a New Flexible Pneumatic Bending Joint

Several typical flexible pneumatic actuators （FPA） and different mechanical models describing their behaviors have been proposed, however, it is difficult to balance compliance and load capacity in conventional designs, and these models still have limitations in predicting behavior of FPAs. A new flexible pneumatic bending joint （FPBJ） with special anisotropic rigidity structure is proposed. The FPBJ is developed as an improvement with regard to existing types of FPA, and its principal characteristic is derived from the special anisotropic rigidity structure. With this structure, the load capacity in the direction perpendicular to bending plane is strengthened. The structure of the new FPBJ is explained and a mathematical model is derived based on Euler-Bernoulli beam model and Hook’s law. To obtain optimum design and usage, some key structure parameters and input-output characteristics are simulated. The simulation results reveal that the relationship between the structure parameters and FPBJ’s bending angle is nonlinear. At last, according to the simulation results, the FPBJ is manufactured with optional parameters and tested. The experimental results show that the joint’s statics characteristics are reflected by the mathematical model accurately when the FPBJ is deflated. The maximum relative error between simulation and experimental results is less than 6%. However, the model still has limitations. When the joint is inflated, the maximum relative error reaches 20%. This paper proposes a new flexible pneumatic bending joint which has sufficient load capacity and compliance, and the mathematical model provides theoretical guidance for the FPBJ’s structure design.

Determining relative block structure rating for rock erodibility evaluation in the case of non-orthogonal joint sets

The most commonly used method for assessing the hydraulic erodibility of rock is Annandale's method.This method is based on a correlation between the erosive force of flowing water and the capacity of rock resistance. This capacity is evaluated using Kirsten's index, which was initially developed to evaluate the excavatability of earth materials. For rocky material, this index is determined according to certain geomechanical factors related to intact rock and rock mass, such as compressive strength of intact rock, rock block size, discontinuity shear strength and relative block structure. To quantify the relative block structure, Kirsten(1982) developed a mathematical expression that accounts for the shape and orientation of the blocks relative to the direction of flow. Kirsten's initial concept for assessing the relative block structure considers that the geological formation is mainly fractured by two joint sets forming an orthogonally fractured system. An adjusted concept is proposed to determine the relative block structure when the fractured system is non-orthogonal where the angle between the planes of the two joint sets is greater or less than 90°. An analysis of the proposed relative block structure rating shows that considering a non-orthogonally fractured system has a significant effect on Kirsten's index and, as a consequence, on the assessment of the hydraulic erodibility of rock.

Fatigue Reliability Assessment of Correlated Welded Web-frame Joints

The objective of this work is to analyze the fatigue reliability of complex welded structures composed of multiple web-frame joints, accounting for correlation effects. A three-dimensional finite element model using the 20-node solid elements is generated. A linear elastic finite element analysis was performed, hotspot stresses in a web-frame joint were analyzed and fatigue damage was quantified employing the S-N approach. The statistical descriptors of the fatigue life of a non-correlated web-frame joint containing several critical hotspots were estimated. The fatigue reliability of a web-frame joint wasmodeled as a series system of correlated components using the Ditlevsen bounds. The fatigue reliability of the entire welded structure with multiple web-frame joints, modeled as a parallel system of non-correlated web-frame joints was also calculated.

Parametric Equation of Stress Concentration Factor for Circular X-Joints Under Axial Loads

In engineering practice, tubular X-joints have been widely used in offshore structures. The fatigue failure of tubular X-joints in offshore engineering is mainly caused by axial tensile stress. In this study, the stress concentration factor distribution along the weld toe in the hot spot stress region for tubular X-joints subject to axial loads have been analyzed by use of finite element method. Through numerical analysis, it has been found that the peak stress concentration factor is located at the saddle position. Thereafter, 80 models have been analyzed, and the effect of the geometric parameters of a tubular X-joint on the stress concentration factor has been investigated. Based on the experimental values of the numerical stress concentration factor, a parametric equation to calculate the stress concentration factor of tubular X-joints has been proposed. The accuracy of this equation has been verified against the requirement of the Fatigue Guidance Review Panel, and the proposed equation is found capable of producing reasonably accurate stress concentration factor values for tubular X-joints subject to axial loads.

Very high cycle fatigue behavior of bridge steel welded joint

Very high cycle fatigue（VHCF） behaviors of bridge steel（Q345） welded joints were investigated using an ultrasonic fatigue test system at room temperature with a stress ratio R = -1. The results show that the fatigue strength of welded joints is dropped by an average of 60% comparing to the base metal and the fatigue failure still occurred beyond 10~7 cycles.The fatigue fracture of welded joints in the low cycle regime generally occurred at the solder while at the heat-affected zone（HAZ） in the very high cycle regime.The fatigue fracture surface was analyzed with scanning electron microscopy（SEM）,showing welding defects such as pore,micro-crack and inclusion were the main factors on decreasing the fatigue properties of welded joints.The effect of welding defects on the fatigue behaviors of welded joints was discussed in terms of experimental results and finite element simulations.

China's First Joint Venture Making NdFeB Magnets——Beijing Century New Magnets Co. Ltd

AFast quenching NdFeB permanent magnet—a high-tech product filling in the domestic gaps—has been put into mass production by the Beijing Century New Magnetics Co. Ltd. Previously, only the United States of America had patent rights for production and sale of fast quenching NdFeB Magnets, and only General Motor Company could produce such high-tech products.

Wall's Beijing Corporation——A Large,Modern Sino-Foreign Ice Cream Joint Venture

Although it was reported that the title of 5000th Sino-foreign joint venture in Beijing had been conferred on Wall’s, it nevertheless remained a strange name to most Beijingers. However, on one of the hottest days last summer, the name Wall’s was seen in the Beijing streets and lanes, the ice-cream kept in small glass refrigerated cases standing under red and blue umbrellas with the trademark of Wall’s on them. This

Iatrogenic atlantoaxial rotatory subluxation after thyroidectomy in a pediatric patient:A case report

BACKGROUND Atlantoaxial rotatory subluxation(AARS)is an uncommon disease with a greater prevalence among children than adults,and it is mostly associated with trauma.Iatrogenic spinal injury accounts for a low percentage of injuries.However,in AARS,20%-40%of cases are associated with surgery,and 48%are caused by infection.Here,we describe our experience with a case of iatrogenic AARS after general anesthesia.CASE SUMMARY A 12-year-old girl presented with right-sided torticollis and cervical motion limit.The patient had undergone thyroidectomy 2 mo ago.Computed tomography revealed AARS with bilateral locked facets.Following the failure of repeated external reduction under general anesthesia,the patient underwent an open surgical reduction.The patient gained atlantoaxial alignment without any complications.Follow-up radiographs showed a normal appearance without instability.The cervical spine of children is more predisposed to injury due to anatomical and biomechanical differences.AARS secondary to infection and surgery is known as Grisel’s syndrome,which involves non-traumatic AARS.Several cases of AARS after surgery and other procedures with no evidence of inflammation have been reported.Our experience shows that surgery requiring hyperextension of the neck after general anesthesia should also be included as a risk factor.CONCLUSION Surgeons and anesthesiologists should be careful not to excessively extend the neck during pediatric surgery.Moreover,clinicians caring for pediatric patients with recent head and neck procedures must be aware of common AARS presentations.

Effect of weld reinforcement on fatigue properties of A6N01 aluminum alloy welded joint

Fatigue properties of smooth and reinforcement A6N01 aluminum alloy welded joints were characterized in this paper. Based on measured S-lgN curves and fatigue fracture morphologies, effect of weld reinforcement on the fatigue property of the welded joint was studied. Results show that the weld toe is the weakness region of the reinforcement welded joint due to the stress concentration in this area, thus the fatigue fracture occurred at the weld toe for all the reinforcement welded joints; while the fatigue property of the smooth welded joint was improved due to remove of the weld reinforcement, and the welding defect was the key factor of the fatigue fracture, thus its fracture zones mainly located at welding zone and fusion line.