A review on evaluation of crack resistance of asphalt mixture by semi-circular bending test

Although there are many kinds of fracture tests to choose from in evaluating the crack resistance of asphalt mixture,the semi-circular bending(SCB)test has attracted a lot of attention in the academic road engineering community because of its simplicity,stability,and flexibility in testing and evaluation.The SCB test has become a common method to study the cracking resistance of asphalt mixture in recent years.This paper mainly summarizes the overview of the SCB test,summarizes some research results and common characterization parameters of the SCB test method in monotone test and fatigue test in recent years,and predicts and suggests the research direction of the SCB test in the future.It is found that the research on the monotonic SCB test is more comprehensive,and the research on the SCB fatigue test needs to be further improved in the aspects of loading mode,characterization parameter selection,and so on.Researchers can flexibly adjust the geometric dimensions and the test parameters of semi-cylindrical specimens,and conduct comprehensive analysis combined with the results of numerical simulation.The crack resistance of asphalt mixture can be comprehensively evaluated by fracture energy,fracture toughness,stiffness,flexibility index and other fracture indicators,combined with the crack propagation of the specimen.The analysis of numerical simulation can confirm the test results.In order to standardize the setting of fatigue parameters for future application,it is necessary to standardize the setting of bending performance.

Extending application of asymmetric semi-circular bend specimen to investigate mixed mode Ⅰ/Ⅱ fracture behavior of granite

The asymmetric semi-circular bend(ASCB)specimen has been proposed to investigate the cracking behavior in different geo and construction materials and attracted the attention of researchers due to its advantages.However,there are few studies on the fracture toughness determination of rock materials.In this work,a series of fracture tests were performed with the ASCB specimens made of granite.The onset of fracture,crack initiation angle and crack propagating trajectory was analyzed in detail combined with several mixed mode fracture criteria.The influence of the crack length on the mode Ⅰ/Ⅱ fracture toughness was studied.A comparison between the fracture toughness ratios predicted by varying criteria and experimental results was conducted.The relationship between experimentally determined crack initiation angles and curves of the generalized maximum tangential stress(GMTS)criterion was obtained.The fracture process of the specimen was recorded with the high-speed camera.The shortcomings of the ASCB specimens for the fracture toughness determination of rock materials were discussed.The results may provide a reference for analysis of mixed mode I and II fracture behavior of brittle materials.

Determination of dynamic modeⅠfracture toughness of rock at ambient high temperatures using notched semi-circular bend method

To investigate the influence of loading rate and high temperature on the dynamic fracture toughness of rock,dynamic fracture tests were carried out on notched semi-circular bend specimens under four temperature conditions based on the split Hopkinson pressure bar system.Experimental and analytical methods were applied to investigating the effect of temperature gradient on the stress waves.A high-speed camera was used to check the fracture characteristics of the specimens.The results demonstrate that the temperature gradient on the bars will not significantly distort the shape of the stress wave.The dynamic force balance is achieved even when the specimens are at a temperature of 400°C.The dynamic fracture toughness linearly develops with the increase of loading rate within the temperature range of 25-400°C,and high temperature has a strengthening effect on the dynamic fracture toughness.

Post-Buckling Behavior of Laminated Composite Cylindrical Shells Subjected to Axial, Bending and Torsion Loads

In present work, post-buckling behavior of imperfect (of eigen form) laminated composite cylindrical shells with different L/D and R/t ratios subjected to axial, bending and torsion loads has been investigated by using an equilibrium path approach in the finite element analysis. The Newton-Raphson approach as well as the arc-length approach is used to ensure the correctness of the equilibrium paths up to the limit point load. Post-buckling behavior of imperfect cylindrical shells with different L/D and R/t ratios of interest is obtained and the theoretical knock-down factors are reported for the considered cylindrical shells.

Micro arc oxidation and electrophoretic deposition effect on damping and sound transmission characteristics of AZ31B magnesium Alloy

Micro arc oxidation(MAO) and electrophoretic deposition(EPD) process are employed to fabricate a dense coating on magnesium alloy to protect it from corrosion in engineering application. The EPD film changes the damping characteristic of magnesium alloy, and both the MAO and EPD process change the bending stiffness of samples being treated. Damping loss factor(DLF) test and sound transmission experiments were carried out for AZ31 B magnesium alloy with coating fabricated by MAO and EPD processes. The results indicate that DLF is improved in frequency range from 0-850 Hz. Bending stiffness of the samples is improved with MAO and EPD treatment. As a result, the sound transmission loss(LST) is improved in the stiffness control stage of the sound transmission verse frequency curve. To the samples by electrophoresis process, the LST is improved in frequency range from 2500-3200 Hz, because the damping loss factor is improved with EPD process. The results are useful for the surface treatment to enhance the damping loss factor, LST and widespread application of magnesium alloy while improving the corrosion resistance.

线缆掩膜中心线代数化重建弯曲半径计算方法

大型电气设备中线缆起到输送、信号传递重要作用,线缆弯曲半径测量是安装过程质量保证的重要环节。针对测量线缆弯曲半径传统方法存在操作不便、效率较低的问题,提出一种非接触式机器视觉线缆弯曲半径测量方法,基于深度学习RGB-D双模态语义分割网络分割线缆掩膜,从掩膜图像中提取线缆特征中心线,进而构建线缆空间特征点集,对缆空间特征点集用参数曲线代数化重建得线缆空间特征曲线,再利用质点空间曲线运动规律求解线缆弯曲半径。为验证本方法实际应用效果,用半径R=110 mm、125 mm标准圆弧固定线缆,由弦高法人工直尺测量结果与本方法测量结果对比,实验表明:本方法测量弯曲半径较人工直尺测量平均误差分别降低7.2%、2.2%,测量时间分别减少93.8%、92.2%。所提出的非接触式的机器视觉线缆弯曲半径测量方法在掩膜图像基础上代数化重建线缆空间特征曲线,计算其空间弯曲半径,测量结果可靠,较人工手动测量精度高、速度快,能适用于各种场合的线缆弯曲半径测量任务。

大直径螺旋埋弧焊管弯曲变形能力的模拟研究

通过有限元模拟研究了基于应变设计的大直径螺旋埋弧焊管的弯曲变形能力。钢管在弯曲载荷下的主要失效模式是管壁局部屈曲变形,通过数值分析得出弯矩、曲率和椭圆度的变化情况,并与外径1067 mm、D/t分别为67和119的两根钢管获得的试验数据进行比较,还分析了材料的实际性能、初始几何缺欠以及残余应力对螺旋埋弧焊管局部屈曲变形的影响。模拟计算得到的临界弯曲应变和曲率与实物试验结果均与现有的经验公式计算结果一致。

有限元分析法改善齿根磨削凸台应力分布研究

通过齿轮理论模型,针对渗碳淬火热处理引起的变形问题,模拟齿轮齿形在磨齿机上的磨削结果,并进行分类建模;利用UG NX12有限元软件分析齿根弯曲应力,寻找其差异与规律,并与国家标准中相关规定及公式进行对比;建立一种虚拟齿根圆弧模型,综合齿轮开齿齿根圆弧与磨削圆弧的模型与理论,尝试推导与标准中齿根有磨削台阶齿轮的应力修正系数部分的差异,找出齿根圆弧与应力的对应关系及降低齿根应力的方法。

Evaluation of fracture properties of epoxy asphalt mixtures by SCB test

The fracture properties of epoxy asphalt mixtures （EAM） are evaluated based on J-integral and ultimate strength. Totally 60 semi-circular bending （SCB）specimens cored from superpave gyratory compactor （SGC）with three groups of notch depths are tested at the temperature of - 10 and 20 ℃. The experimental results reveal good repeatability in EAM characterization. The tensile strength ratio of SCB to the indirect tensile test （IDT） is at a range of 1.4 to 1.7, and the ultimate strength of EAM is exponentially dependent on the notch depths. At the test temperatures, the critical J-integral value of EAM is much higher than that of hot mix asphalt（ HMA） with thermoplastic asphalt binder. The response mode of EAM changes from ductile mode to brittle mode and the fracture energy increases 30% when temperature decreases from 20 to - 10℃, while its critical J-integral value decreases only 15%. It is concluded that EAM has better fracture resistance than thermo-plastic HMA; more fracture energy is needed to initiate cracks in EAM at low temperature, and the cracks propagate more rapidly than at room temperature.

三种Cu基自蔓延焊接材料焊接接头性能的研究

将自蔓延高温合成技术应用于焊接上,开发了几种可焊不同厚度的新型Cu基自蔓延焊接材料,对其焊缝的组织形貌及性能进行了研究。结果表明,自蔓延反应后形成熔焊连接,焊缝与基体之间存在明显的过渡区,焊缝的拉伸强度均大于200MPa,弯曲强度最高接近600MPa,表面硬度可达120HRB,满足了金属间快速焊接的需要。

中厚板轧制过程头部弯曲成因分析及其控制

针对国内中厚板轧机普遍存在的头部弯曲问题,通过对轧制过程进行分析,得出轧件上下表面温差和上下辊辊径比对轧件头部弯曲的影响规律,建立轧件头部弯曲曲率、轧机上下辊辊径比和轧件上下表面温差之间的关系模型.利用该模型可以根据轧制参数预测轧件弯曲曲率,为现场配辊提供理论依据.提出一种采用CCD摄像机测量轧件弯曲曲率的测量方法.

大型直缝焊管多点弯曲一次性矫直新工艺原理

由于大型直缝焊管的特殊性,多采用三点弯曲多次矫直的方法修正其直线度。基于平面弯曲弹复理论及过弯矫直等价原理,给出基于管件初始挠度曲线分布的理论矫直弯矩,施加该理论弯矩可将管件一次性完全矫直。为方便工业应用,将该弯矩离散线性化,提出多点弯曲一次性矫直控制策略,并给出相应的工艺参数的确定方法。通过实测大型管件挠度分布,建立大型管件多点弯曲一次性矫直的数值仿真模型,并以小尺寸管件的物理模拟试验验证仿真模型的可靠性。对实际管件的仿真模拟结果验证多点弯曲一次性矫直控制策略的可行性,为全自动矫直机的设计和应用提供理论基础。

薄壁管数控弯曲成形中芯轴参数的确定

在薄壁管数控弯曲成形中,诸多错综复杂且相互耦合的物理因素严重影响弯管成形质量,其中芯轴是一个极为重要的因素,选取芯轴伸出量和球头节个数是实际生产中关键,且是难题所在。基于薄壁管绕弯成形原理,提出芯轴球头节个数和芯轴伸出量的计算公式。建立精确有限元模型对薄壁管数控弯曲成形进行力学仿真,得出芯轴参数对壁厚变化率和椭圆畸变率的影响规律,验证了芯轴伸出量计算公式。

基于ANSYS的双圆弧齿轮弯曲应力有限元分析

利用ANSYS的参数化设计语言(APDL)建立双圆弧齿轮的三维实体,形成相应有限元模型,对轮齿弯曲应力进行了分析。总结了名义压力角和齿形工艺角对轮齿弯曲应力的影响规律,并得出跑合前最大弯曲应力发生在齿腰处的结论,为双圆弧齿轮的设计和使用提供理论依据。

基于高弯曲强度的齿轮过渡曲线分析

齿根过渡曲线是影响齿轮弯曲强度的重要因素。为了提高齿轮弯曲强度,延长齿轮的工作寿命,从齿轮根部过渡曲线的加工刀具设计入手,分别考虑圆角刀顶、单圆弧刀顶、双圆弧刀顶,建立齿轮过渡曲线成形方程,确定齿轮根部强度敏感部位和应力集中系数的关系模型,探究齿轮不同过渡曲线对齿轮弯曲强度的影响,用有限元法对理论分析计算的结果进行验证。研究表明:使用双圆弧刀顶的刀具加工出的齿轮,其齿根弯曲强度比普通齿轮的齿根弯曲强度有很大提高,为高弯曲强度齿轮设计提供理论依据。

大型直缝焊管四点弯曲JCO成形及其弹复解析

提出了一种大型直缝焊管生产的新工艺——四点弯曲JCO成形,采用该工艺最终成形的管坯径向截面的几何形状为曲率一致的圆,且成形道次少,生产效率高。通过宽板四点弯曲试验,验证了理论解析的正确性,为将来实际生产中通过调整凸模行程控制成形管坯曲率提供了理论依据。理论和试验数据均表明弹复前后的曲率为线性关系,这为四点弯曲JCO成形过程智能化控制提供了便捷。基于上述理论进行了管坯四点弯曲JCO成形试验,获得了理想成形管坯,且成形道次仅13道次,相对传统工艺25道次,生产效率得到显著提高。

东营凹陷中央背斜隆起带形成机制分析

重建了东营凹陷构造演化过程 ,提出在盆地古近纪同裂陷期充填序列中 ,沙三段底界面S6′界面具有构造变格意义 ,过该界面盆地的构造应力场发生了由近南北向拉伸到NW—SE向拉伸的转换。在此基础上重新解析了盆地中央背斜隆起带 ,并指出中央背斜带是一个复合的构造系统。其东段的辛镇背斜的性质为受控于陈南铲式断层的大型伸展断弯褶皱 ,主要的活动期为Ek—Es下3 时期 ;而其西段为东营—梁家楼—现河弧形生长滑脱断裂系统的组成部分 ,主要形成于Es上3 —Es2 沉积时期。上述认识对于中央背斜隆起带油气勘探具有重要的意义。

双圆弧齿轮齿根弯曲应力的研究

用三维边界元素法对 GB- 12 75 9- 91双圆弧齿轮的轮齿弯曲应力进行了分析计算。并在此基础上得出齿根应力沿齿长的分布。

EH36钢埋弧焊接头CTOD试验中的突跃效应及评价

根据BS 74 4 8试验标准 ,在对海洋石油平台用钢EH36单、双丝埋弧焊接头的焊缝和热影响区 (HAZ)进行低温下 (- 15℃ )裂纹尖端张开位移 (CTOD)测试时 ,多个试样出现了”突跃”(F -V曲线上瞬间载荷下降、位移增加变慢 ) ,亦称”POP -IN”现象。针对这一问题 ,依据BS 74 4 8-Ⅰ中的有关评定标准 ,对存在POP -IN现象的试样进行了F-V曲线上载荷 -位移变化的测量、计算 ,并在光学显微镜 (× 10 0 0 )下观察了断裂面上脆性起裂点处的微观组织 ,从而合理取舍了焊接接头这一非均质结构中出现的POP -IN效应。

电弧螺柱焊中实现螺柱的低速送进

螺柱送进速度是电弧螺柱焊中的一个重要参数。基于对工程中广泛应用的电磁式螺柱焊枪工作原理的深入分析,提出螺柱低速送进的同时提供足够的挤压力可以实现电弧螺柱焊接,研制开发了步进式电弧螺柱焊枪及其控制系统。作为实现螺柱低速送进的焊枪,其动力机构为步进电机,螺旋传动装置为运动机构主体,保证螺柱低速送进时对接头处金属具有足够的挤压力。试验结果表明,采用步进式电弧螺柱焊枪,螺柱低速送进可以完成电弧螺柱焊过程;弯曲试验结果表明螺柱焊接头能满足使用要求。