Detection of internal crack growth in polyethylene pipe using guided wave ultrasonic testing

Despite the success of guided wave ultrasonic inspection for internal defect detection in steel pipes,its application on polyethylene(PE)pipe remains relatively unexplored.The growth of internal cracks in PE pipe severely affects its pressure-holding capacity,hence the early detection of internal cracks is crucial for effective pipeline maintenance strategies.This study extends the scope of guided wave-based ultrasonic testing to detect the growth of internal cracks in a natural gas distribution PE pipe.Laboratory experiments and a finite element model were planned to study the wave-crack interaction at different stages of axially oriented internal crack growth with a piezoceramic transducer-based setup arranged in a pitch-catch configuration.Mode dispersion analysis supplemented with preliminary experiments was performed to isolate the optimal inspection frequency,leading to the selection of the T(0,1)mode at 50-kHz for the investigation.A transmission index based on the energy of the T(0,1)mode was developed to trace the extent of simulated crack growth.The findings revealed an inverse linear correlation between the transmission index and the crack depth for crack growth beyond 20%crack depth.

Parametric study on single shot peening by dimensional analysis method incorporated with finite element method

Shot peening is a widely used surface treatment method by generating compressive residual stress near the surface of metallic materials to increase fatigue life and re- sistance to corrosion fatigue, cracking, etc. Compressive re- sidual stress and dent profile are important factors to eval- uate the effectiveness of shot peening process. In this pa- per, the influence of dimensionless parameters on maximum compressive residual stress and maximum depth of the dent were investigated. Firstly, dimensionless relations of pro- cessing parameters that affect the maximum compressive residual stress and the maximum depth of the dent were de- duced by dimensional analysis method. Secondly, the in- fluence of each dimensionless parameter on dimensionless variables was investigated by the finite element method. Fur- thermore, related empirical formulas were given for each di- mensionless parameter based on the simulation results. Fi- nally, comparison was made and good agreement was found between the simulation results and the empirical formula, which shows that a useful approach is provided in this pa- per for analyzing the influence of each individual parameter.

A Numerical Study Comparing the Effect on Residual Stresses of Two Different Types of Projectiles During Shot Peening

Shot peening is a widely used technique to improve fatigue life in metallic alloys.This processing technique introduces a subsurface compressive residual stress field through a plastic deformation of the surface caused by the impact of a large number of high-speed projectiles.There are a number of parameters that affect the residual stress field depth and magnitude.The effects of the impact angle,shot speed and shot geometry are currently being researched.In particular,substituting spherical cast shots by cylindrical cut wire shots is an attractive option,especially in terms of cost.The effect of shot geometry on residual stresses,however,needs to be further investigated.Because industrial-scale experimentation is costly and cumbersome,mathematical modeling offers a convenient alternative to carry out this type of research.The present work shows a comparison between the residual stresses generated by the impact of spherical and cylindrical projectiles on a steel substrate.This threedimensional model was developed using ABAQUS finite element commercial software(Release 6.12,Dassault Systémes,France).The results show that cylindrical shots generate residual stress fields t hat a re higher in magnitude than t hose generated by a spherical shot.However,the residual stress field of cylindrical shots impacting the surface at an oblique angle shows an important degree of asymmetry.This effect is not found when spherical shots impact the surface at the same oblique angle.

Experimental and numerical studies of nonlinear ultrasonic responses on plastic deformation in weld joints

The experimental measurements and numerical simulations are performed to study ultrasonic nonlinear responses from the plastic deformation in weld joints. The ultrasonic nonlinear signals are measured in the plastic deformed30Cr2Ni4 Mo V specimens, and the results show that the nonlinear parameter monotonically increases with the plastic strain, and that the variation of nonlinear parameter in the weld region is maximal compared with those in the heat-affected zone and base regions. Microscopic images relating to the microstructure evolution of the weld region are studied to reveal that the change of nonlinear parameter is mainly attributed to dislocation evolutions in the process of plastic deformation loading. Meanwhile, the finite element model is developed to investigate nonlinear behaviors of ultrasonic waves propagating in a plastic deformed material based on the nonlinear stress–strain constitutive relationship in a medium. Moreover, a pinned string model is adopted to simulate dislocation evolution during plastic damages. The simulation and experimental results show that they are in good consistency with each other, and reveal a rising acoustic nonlinearity due to the variations of dislocation length and density and the resulting stress concentration.

喷丸工艺参数对718镍基合金表面性能的影响

为全面理解718镍基合金喷丸强化工艺参数的作用,用精确的三维建模对弹丸和基体进行模拟,并结合仿真分析方法考察喷丸尺寸、速度及入射角度对喷丸强化的影响。重点分析了表面粗糙度和残余应力分布,以全面展现喷丸强化的关键特征。结果表明:随弹丸直径和速度的增加,残余应力呈规律性变化,入射角度为0°~10°时对残余应力影响较小,但可轻微降低表面粗糙度。当入射角度从10°增至30°时,喷丸强化效果减弱,同时表面粗糙度增加。这为工艺参数选择提供了重要参考。通过试验验证仿真结果,进一步证实了本研究的准确性和实用性。

基于有限元仿真的钛合金喷丸技术应用综述

喷丸强化工艺作为一种常用的表面强化技术,在钛合金相关零部件的表面强化中起到重要作用,有限元技术在探究喷丸强化工艺机理和强化效果中应用广泛。目前,多数喷丸仿真研究都是以钢和铝合金为材料,以钛合金为材料的喷丸仿真研究相对较少。本文总结了国内外学者关于钛合金传统喷丸仿真技术、钛合金新型喷丸仿真技术以及钛合金传统喷丸技术与新型喷丸仿真技术的联系,并对钛合金喷丸仿真方面的发展趋势进行展望。

薄橡胶层改善喷丸质量机理研究

目的 为了解决喷丸导致的金属表面粗糙度提升问题,方法 提出在金属表面铺设薄层橡胶层,通过薄橡胶层的变形均匀化丸粒的冲击压力,进而抑制丸粒冲击所造成的粗糙度急剧增加的新工艺。为验证新工艺的可行性并揭示其机理,采用有限元软件Abaqus分别建立传统喷丸、黏结橡胶层喷丸和自由铺设橡胶层喷丸的仿真模型;设定丸粒为半径0.5 mm的球形刚体,丸粒初始速度为50 m/s;工件材料为Q235,采用Johnson-Cook本构模型;薄层橡胶采用双参数Mooney-Rivlin本构模型;仿真模型中不同部件之间的摩擦系数均设定为0.2;所有模型均采用显式求解方法。结果 在传统喷丸、黏结薄橡胶层喷丸和自由铺设橡胶喷丸条件下,工件表面丸粒冲击点的残余压应力分别为96,343,252 MPa,工件表层最大残余压应力分别为391,426,373 MPa,工件表面的残余压应力得到显著提升;3种喷丸工艺下冲击压痕分别为56.2,26.1,35.4μm,表面薄层橡胶有效降低了工件表面粗糙度;工件表层残余应力的分布形式与橡胶层的厚度密切相关,当橡胶厚度分别为0.05,0.20 mm时,所得到的最大残余压应力分别为329,373 MPa,距离工件表面分别为256,141μm。结论 在机理上,橡胶的大变形特征增大了丸粒的冲击作用面积,延长了冲击作用时间,是薄橡胶层能够改善喷丸质量的根本原因。

驻波型直线超声波电机接触特性有限元建模与分析

超声波电机接触摩擦是影响电机性能的关键环节,建立超声波电机的接触模型对电机性能优化具有重要作用。现有对驻波型超声波电机接触问题的研究,大多采用解析法,需要采用较多的简化假设,难以准确反映电机实际结构及真实接触情况。针对这一问题,采用有限元法,对驻波型直线超声波电机接触特性进行建模和分析。首先,考虑定子复合结构,建立定子三维有限元模型,分析定子在外加电压作用下的振动响应,得到定子振动位移表达式。在此基础上,考虑定子与动子的结构和接触特点,建立定、动子接触三维有限元模型。基于所建立的模型,分析了定、动子的接触状态、接触压力分布,并研究了驱动电压大小和预压力变化对接触特性和电机性能的影响。最后,搭建试验测试平台,测量了电机的输出特性,并与理论计算值进行对比,对比结果验证了所建立的定、动子三维有限元接触模型。

A unifying approach in simulating the shot peening process using a 3D random representative volume finite element model

Using a modified 3D random representative volume（RV）finite element model,the effects of model dimensions（impact region and interval between impact and representative regions）,model shapes（rectangular,square,and circular）,and peening-induced thermal softening on resultant critical quantities（residual stress,Almen intensity,coverage,and arc height）after shot peening are systematically examined.A new quantity,i.e.,the interval between impact and representative regions,is introduced and its optimal value is first determined to eliminate any boundary effect on shot peening results.Then,model dimensions are respectively assessed for all model shapes to reflect the actual shot peening process,based on which shape-independent critical shot peening quantities are obtained.Further,it is found that thermal softening of the target material due to shot peening leads to variances of the surface residual stress and arc height,demonstrating the necessity of considering the thermal effect in a constitutive material model of shot peeing.Our study clarifies some of the finite element modeling aspects and lays the ground for accurate modeling of the SP process.

有限元模拟和神经网络相结合的喷丸处理SAE9254钢疲劳寿命预测

采用ABAQUS有限元软件建立基于Python脚本的随机多弹丸喷丸模型,对不同弹丸直径、不同弹丸速度和不同喷丸覆盖率下喷丸处理后悬架弹簧用SAE9254钢的残余应力分布和表面粗糙度进行预测,并与试验结果进行对比;基于有限元模拟结果结合神经网络模型对试验钢的疲劳寿命进行预测,并进行试验验证。结果表明:模拟得到SAE9254钢的残余应力沿深度方向的变化曲线与试验结果吻合较好,最大残余压应力的相对误差约为14.77%,表面粗糙度的相对误差约为3.18%,建立的随机多弹丸喷丸模型能够准确地预测SAE9254钢喷丸后的残余应力分布及表面粗糙度。采用有限元模拟与神经网络相结合的方法得到的疲劳寿命预测值和试验值的平均相对误差为6.85%,该方法可以准确地预测SAE9254钢的疲劳寿命。

有限元模拟再喷丸参数对Q345B钢残余应力演变规律的影响

对退火态Q345B钢依次进行喷丸、预疲劳、再喷丸处理,采用X射线/剥层法研究了再喷丸对残余应力和疲劳寿命的影响,以预疲劳的残余应力为初始应力,构建了随机弹丸再喷丸有限元模型,研究了覆盖率(100%,200%,300%)、弹丸直径(0.4,0.5,0.6,0.7mm)和弹丸初速度(25,35,40,45m·s^(-1))对残余应力分布及其影响层深度和试样表面粗糙度的影响。结果表明:再喷丸处理可以使预疲劳处理松弛的残余应力基本恢复到单次喷丸后的水平,并进一步延长其疲劳寿命。有限元模拟得到,随着覆盖率增加,再喷丸引入的残余压应力和影响层深度无明显变化,试样表面粗糙度增大;随着弹丸直径和弹丸初速度增加,残余压应力和影响层深度均先增大后趋于稳定,表面粗糙度增大。最优再喷丸参数为弹丸初速度40m·s^(-1),弹丸直径0.6mm,覆盖率100%。

弧齿锥齿轮喷丸表面微观形貌仿真与试验验证

喷丸强化工艺能在弧齿锥齿轮表面及次表面引入残余压应力场,提高其疲劳寿命;但工程应用中经常出现不适当的喷丸参数,导致齿轮表面粗糙度显著增加,影响了齿面制造质量。为了准确预测与调控喷丸后齿轮表面微观形貌及表面粗糙度,基于离散元和有限元耦合的方法,提出了一种弧齿锥齿轮齿面喷丸工艺仿真计算方法,表面粗糙度预测与实测误差在20%以内,表明仿真预测方法具有准确性。基于该方法,以某弧齿锥齿轮为研究对象,研究了不同喷丸工艺参数与喷丸后齿面微观形貌的关联规律。研究结果表明,①随着喷丸时间增加,齿面三维粗糙度Sa先显著增加后缓慢下降;②当喷丸时间为50 s时,在本文的工艺参数下能达到满覆盖率;③弹丸速度与弹丸直径对齿面粗糙度均有较大的影响,但弹丸直径的影响更为显著。研究工作为喷丸后弧齿锥齿轮表面的微观形貌准确数值模拟与预测提供了方法基础,为合理制定喷丸工艺参数提供了技术参考。

超声冲击对钢桥焊缝耐腐蚀性能的影响

为研究超声冲击对钢桥焊缝部位耐盐雾腐蚀性能的影响,对焊缝试件进行超声冲击并进行盐雾腐蚀试验,通过金相试验分析了焊缝超声冲击后的表面微观形貌.建立焊缝盐雾腐蚀有限元模型,对比了不同冲击时间下试件的腐蚀深度、表面电位和表面电流密度.结果表明:超声冲击细化了表面晶粒尺寸,减少晶界碳化物占比,有效降低试件的腐蚀敏感性.随着超声冲击时间的增加,试件耐盐雾腐蚀性能先升高后降低.当超声冲击时间为180 s及冲击速度为3 mm^(2)/s时,试件耐盐雾腐蚀性能表现出最优.

基于GA-SVM的超声切削力预测模型研究

Nomex蜂窝材料是难加工材料,选择合适的加工方法和加工参数对于控制切削力和提高加工质量非常重要,开展了超声辅助切削Nomex蜂窝材料的三维有限元仿真,对前期的超声切削Nomex蜂窝材料加工试验进行分析,针对影响切削力的加工参数设计正交试验,构建基于支持向量机(SVM)的超声切割切削力预测模型,提出一种遗传算法(GA)优化参数方法,设定该模型的最终真实值与预测值的相对误差在0~3.55%范围内且R^(2)=0.9966,选取4组不同于正交试验表的加工参数进行验证。结果表明,该方法有效可行,对选择合适的加工参数、减小切削力具有积极意义。

7075铝合金喷丸参数影响的数值仿真及实验研究

为探究7075铝合金喷丸加工过程中不同喷丸参数对于喷丸结果的影响,本文基于Abaqus软件对相应的喷丸过程进行了有限元仿真,观察不同喷丸参数对于表面残余应力分布、表面粗糙度以及表面三维形貌的影响,同时基于实验过程对相应的喷丸过程进行研究,并对仿真和实验所得到的结果进行对比,最终发现,虽然在具体数值上两者之间存在一定的差距,但在变化趋势上两者呈现较为明显的一致性。因此,可以认为两者的分析结果是较为可信的,同时得出在单纯调整弹丸尺寸和弹丸速度的条件下,表面残余应力和表面粗糙度两者难以同时兼顾,但是喷丸覆盖率的提高可以用降低生产效率为成本较好的兼顾这两方面。

大尺寸铝合金薄壁零件喷丸校形仿真分析

针对零件的缘条和薄壁板面的局部变形喷丸校形问题,在喷丸成形和校形的理论基础上,建立了大型铝合金框零件喷丸校形仿真方法;并以局部缘条超差喷丸校形为例,利用提出的喷丸校形有限元仿真方法进行了参数化分析与讨论;最后通过理论和试验验证了仿真方法预测的准确性。结果表明,利用提出的仿真方法可以实现大型铝合金框类薄壁变厚度复杂零件局部高缘条喷丸校形效果的预测。以局部缘条边缘中间点校形效果为例,校形效果与缘条厚度和缘条宽度等局部结构因素有关;缘条越厚、宽度越小,同样的喷丸强度下校形效果越不明显;此外,校形量还受到材料初始应力的影响;且在一定范围内,通过增加喷丸强度有利于提高缘条的校形效果,但喷丸校形效果有一定的上限。

基于有限元法的超声辅助线锯单晶硅表面粗糙度影响规律

为研究超声振动辅助切割单晶硅对硅片的表面粗糙度的影响,利用ABAQUS软件建立单颗磨粒切割单晶硅的二维仿真模型,通过响应面法(RSM)分析仿真数据,获得单晶硅表面粗糙度与设定的线切割工艺参数之间的交互关系,研究单颗磨粒在不同工艺参数下对单晶硅表面粗糙度的影响。研究结果表明,通过建立评价表面粗糙度与工艺参数之间的回归模型,并对模型进行目标优化,得到最佳的工艺参数为:超声频率f=31 kHz,超声振幅A=10μm,磨粒速度vl=28 m/s,磨粒倾角θ=-15°,磨粒半锥角φ=60°。

Process-based deep learning model:3D prediction method for shot peen forming of an aircraft panel

Shot peen-forming is a more precise method of forming aircraft panels than conventional methods.The traditional method of acquiring the process parameters relies mainly on prior theoretical knowledge and trial-and-error.Despite the finite element method’s ability to replace some experimentation,it still cannot realize the design of shot peen forming processes parameters of an aircraft panel based on a known contour.This study uses an innovative model-based deep learning approach to predict aircraft panel deformation and active design the shot peening parameters.The prediction time is less than 1 second,resulting in a significant reduction in computational time.The shot peen forming process parameters and the geometric structure characteristics of the aircraft panel are divided into independent channels to establish a high-dimensional feature map,which are used to train the deep learning model.The forming contours of the 2024-T351 high-strength aluminum alloy panel are predicted under different shot peening processes.In addition,the process parameters are designed according to the known contour of the forming process.To verify the precision of the proposed method,the designed shot peen forming process is used to manufacture a single curvature aircraft panel with a curvature radius of 3500 mm.There is good agreement between the forming contour and the theoretical design contour.The maximum deformation error is less than 1 mm and its mean error is 7.8%.The mean curvature radius error is 5.668%.The proposed method provides a new and practical reference to the precise design of the shot peen-forming process.

20Cr2Ni4齿轮钢激光喷丸和机械喷丸残余应力场有限元模拟

使用有限元软件建立了20Cr2Ni4齿轮钢喷丸强化的三维数值分析模型,探究了激光喷丸(LSP)与机械喷丸(SP)在不同工艺参数下的残余应力场,分析了网格尺寸对模拟结果的影响,建立了复合喷丸的有限元网格模型,研究了不同复合方式的喷丸对残余应力场的影响。结果表明,激光喷丸有限元分析中,网格尺寸一般控制在0.1 mm以下,相较于激光喷丸,机械喷丸对网格密度的要求比较高。当弹丸直径为Φ0.5 mm,且冲击区域最小单元网格尺寸为0.03 mm以下时,模拟结果有效。相较于激光喷丸,LSP-SP复合喷丸在表面产生的残余压应力略有提升,应力在靶材表面没有被严重的削弱。复合喷丸的残余压应力层深可以达到机械喷丸的2~3倍;在深度方向的最大残余压应力可以达到材料屈服强度的1.5倍。

9310钢螺旋锥齿轮喷丸强化残余应力场计算仿真研究

喷丸加工诱导零件表面产生残余压应力场以提高零件疲劳寿命,是螺旋锥齿轮的关键强化工艺。为准确计算喷丸后齿面残余应力场,基于离散元与有限元耦合的方法提出一种螺旋锥齿轮喷丸工艺计算仿真模型。模型计算结果与试验结果误差在10%以内,表明模型可准确预测齿面残余应力分布。基于该模型,以AISI 9310材料螺旋锥齿轮为研究对象,探讨了喷丸工艺参数与残余应力场特征参数的关联规律。研究发现,本文所用工艺参数加工:(1)喷丸工艺主要影响轮齿表层50μm内的残余应力场;(2)喷丸覆盖率为200%时,弹丸直径和速度的改变,对表面残余压应力影响较小;(3)当弹丸速度和直径提高时,靶板表层最大残余压应力值和最大残余压应力深度都得到明显提高,其中最大残余压应力值可提高到–1251.5 MPa,最大残余压应力深度可提高到40μm。本文建立的残余应力计算模型为螺旋锥齿轮的喷丸工艺参数优选提供了计算工具与方法,把依赖试错迭代的工艺方法上升到可计算、可预测的层面。