SIMULATION OF VIBRATION STRESS RELIEF AFTER WELDING BASED ON FEM

A finite element model is developed for the simulation of vibration stress relief （VSR） after welding. For the nonresonant vibration, the reduction in stress strongly depends on the amplitude of vibration. For the resonant vibration, the vibration frequency is the key for stress relief. The vibration frequency should be close to the structure natural frequency for the desired vibration mode. Only small vibration amplitude is required, which will be amplified during vibration. Vibration time does not have a major impact on vibration stress relief. When the amplitude of vibration stress relief is large, the treatment will be more effective.

TECHNOLOGY OF QUANTITATIVE ANALYSIS ON VIBRATORY STRESS RELIEF BASED ON ULTRASONIC TIME-OF-ARRIVAL METHOD

The effect of vibratory stress relief （VSR） is usually evaluated with the indirect method of observing the change of amplitude frequency response characteristics of structures. A new kind of evaluating method of VSR based on the ultrasonic time-of-arrival method （UTM）, which can obtain the residual stress directly through measuring the propagation time of ultrasonic wave in the material, is presented. At first, the principle of the measuring method of residual stress based on UTM is analyzed. Then the measuring system of the method is described, which is in virtue of ultrasonic flaw detector and high-sampling-rate digital oscillograph. And a set of calibration system that contains a piece of standard specimen is also introduced. Experimental results prove the relation between the residual stress and the propagation time of ultrasonic in workpieces. Finally, the measuring and calibration systems are applied in evaluating the effect of VSR. The final test results show that the method is effective.

A Numerical Investigation of the Stress Relief Zones Around a Longwall Face in the Lower Seam for Gas Drainage Considerations

Extraction of a protective coal seam (PVCS)-below or above a coal seam to be mined with the potential of coal andgas outburst risk-plays an important role not only in decreasing the stress field in the surrounding rock mass but alsoin increasing the gas desorption capacity and gas flow permeability in the protected coal seam (PTCS). The PVCSis mined to guarantee the safe mining of the PTCS. This study has numerically evaluated the stress redistributioneffects using FLAC3D model for a longwall face in Shanxi Province. The effects of mining depth, mining height andinter-burden rock mass properties were evaluated using the stress relief angle and stress relief coefficient. Verticalstress distribution, stress relief angle and stress relief coefficient in the PTCS were analyzed as the face advancedin the PVCS. The results showed that the stress relief achieved in different locations of the PTCS varied as the faceadvanced. Sensitivity analyses on the pertinent variables indicate that the stress relief in the PTCS is affected mostby the mining depth followed by the inter-burden lithology and the mining height. Furthermore, the elastic moduliof different layers within the inter-burden rock mass are more important than their uniaxial compressive strength(UCS) and Poisson’s ratio. These observations can guide gas drainage borehole design to minimize the accidentsof coal and gas outbursts.

Influence of Cultural Alienation on Happiness of Overseas Students: Mediating Role of Stress Relief and Regulating Role of Cultural Intelligence

When the global outbreak of new coronary pneumonia broke out in 2020,online public opinion events triggered by cultural differences among overseas students had come into the public view.To further explore the relationship between the cultural alienation of overseas students and their own happiness,this study takes visualization and analysis of positive,negative sentiment analysis of Weibo netizens’comment data in the“Xu Kexin Incident”as the starting point,on the basis of introducing cultural alienation,stress relief methods,and cultural intelligence,combining gender and social ability,social relations and other individual attributes,designed a questionnaire to investigate 502 overseas students,through the construction and analysis of the adjusted Cox risk ratio intermedi-ary model,comprehensive single factor interference and multi-factor cross-over comprehensive analysis.The results show that the cultural alienation of overseas students has a significant effect on their own well-being.The study concluded as follows:(1)Netizens hold polarized views on the three dimensions of overseas students’mask,safety,and culture;(2)Stress relief methods play an intermediary role between cultural alienation and the happiness of overseas students,among which Negative stress relief methods play a greater role;(3)The level of cultural intelligence regulates the intermediary process of stress relief methods.The higher the level of cultural intelligence,the stronger the regulatory effect.

Evaluation of residual stress relief of aluminum alloy 7050 by using crack compliance method

High strength aluminum alloys of 7xxx series have unacceptable levels of quenching residual stresses from solution heat treatment. The residual stress not only results in machining distortion and dimensional instability, but also increases the possibility of stress corrosion cracks. Therefore, it is necessary to reduce the residual stress to an acceptable level. The crack compliance method was adopted to study the influences of various stress relief methods on residual stress patterns in 7050 aluminum alloy. The results show that 90% residual stress can be eliminated by the cold stretching(Tx51) method. And a lower level of residual stress can be achieved by the uphill quenching(Tx53) method or the cold compression(Tx52). However, there is a very steep residual stress gradient normal to exterior surfaces.

Mechanism of Stress Relief Cracking in a Granular Bainitic Steel

Coarse-grained heat-affected zone（CGHAZ） of a low alloyed,granular bainitic steel T24 was simulated in a Gleeble apparatus.The stress relief of the CGHAZ was analyzed by annealing the samples.The morphology and behavior of the microstructure near the grain boundaries during stress relief were investigated by means of focused ion beam,in situ tensile testing,transmission electron microscopy,scanning electron microscopy and electron back-scatter diffraction.It was observed that there were large martensite/austenite islands distributed along the grain boundaries of CGHAZ.During stress relief at elevated temperature,the retained austenite at the grain boundaries decomposed into M3C carbides and a ferrite forming softening zone.Together with the stress relief,piled up of dislocations occurred within the ferrite in the area adjacent to the ferrite/M3C interface,which resulted in high level of stress accumulation and caused crack initiation along the grain boundaries.These results indicate that the stress relief induced the grain boundary crack is controlled by other mechanisms rather than the creep-like grain boundary sliding.

Principle of in-situ 3D rock stress measurement with borehole wall stress relief method and its preliminary applications to determination of in-situ rock stress orientation and magnitude in Jinping hydropower station

As a main constituent of geological body, the rock masses have distinct differences from other materials, one of which is that rock masses are initially stressed in their natural states. Hence, it is an extremely challenging and significant research project to know the present residual stress of the rock masses in the earth's crust. Although some regularities of distribution of in-situ rock stresses can be deduced, the basic means to study the state of rock stress is in-situ stress measurement. After a brief review of several measuring methods of in-situ 3D rock stress, a new one, borehole wall stress relief method (BWSRM) to determine the in-situ 3D rock stress tensor in a single drilled borehole was proposed. Based on the principle of in-situ rock stress measurement with BWSRM, an original geostress measuring instrument was designed and manufactured. Preliminary experiments for determination of in-situ stress orientation and magnitude were carried out at an experimental tunnel in Jinping Ⅱ hydropower station in China, where the buried depth of overburden was about 2430 m. The results showed that it was feasible to measure the in-situ 3D rock stresses with BWSRM presented in this paper. The BWSRM has a broad prospect for in-situ 3D rock stress measurements in practical rock engineering.

Non-complete relief method for measuring surface stresses in surrounding rocks

The measurement of surface stresses in surrounding rocks with the use of a relief method of annular hole-drilling was studied by numerical analysis. The stress relief process by hole-drilling was then simulated with the use of finite element method. The influences of the borehole diameter(d), the initial stresses and the ratio of the initial principle stresses on the variations of the remained stress and the released stress in function of the relief depth(h) were discussed. The relation between the non-dimensional ratio of the released principle strains and that of the initial principle stresses, and the effect of the elastic modulus and the Poisson ratio of the rock mass on the stress relief curves were studied. The results show that the stress relief behavior formulated with the non-dimensional ratio of the released stress and the ratio of h/d is only sensitive to the ratio of the initial principle stresses and the Poisson ratio. The stresses are completely released when h equals 1.6d, and the tensile stresses take place on the bore core surface in the relief measurement process. Finally, a non-complete relief method of annular hole-drilling for measuring surface stress in surrounding rocks is proposed and the procedure is presented.

首山一矿深部地应力分布规律及影响因素

为探讨平顶山首山一矿深部地应力分布规律及其影响因素,基于矿井实测地应力数据,运用构造物理学、岩石力学和数值模拟方法,研究了测点地应力类型、大小和方向分布规律,反演了地应力场分布特征,分析了埋深、岩性和地质构造对地应力的影响,确定了影响地应力分布的主控因素。研究表明:多元回归反演分析法获得的地应力计算值与实测值吻合,相对误差小于20%,结果可靠。矿井煤岩体处于三维压应力状态,煤层主应力关系为S_(H)>S_(V)>S_(h),地应力由矿井北部向南部呈现先增大后减小再增大的变化趋势,地应力为28~44 MPa,属于高应力水平,地应力方向为NEE向。埋深影响地应力大小和类型,随埋深增加主应力增大,应力场类型向准静水压力场过渡;岩性与地应力密切相关,从泥岩到砂岩或灰岩,地应力增大,弹性模量越大地应力越大,地层岩性的差异造成地应力大小离散分布、应力方向偏转角不超过10°;矿井地应力与埋深、弹性模量的关系可表示为σH=0.0350H+0.4681E−8.5513。地质构造是影响首山一矿地应力分布的主控因素,褶皱形态控制地应力的水平应力分布,向斜内弧应力值大于背斜内弧,且褶皱弯曲程度越大,其内弧地应力越大,应力梯度越大;断层带内应力降低、断层尖灭端应力集中,地应力方向沿着断层走向偏转,与断层走向夹角越大,应力方向偏转角越大;断层切割复式褶皱时,断层与向斜构造组合区应力值大于断层与背斜构造组合区,且断褶构造组合造成地应力方向分布紊乱。

底板动压巷道压裂弱结构体应力转移控制技术

为了满足煤矿安全生产的需要,许多巷道都会布置在煤层底板中,如部分运输大巷、排水巷道、瓦斯抽采巷道等。采动应力容易造成底板巷道围岩应力升高,加剧底板巷道围岩变形,造成支护永久失效、顶板下沉、巷道底鼓、两帮收敛等破坏。针对此,提出了在应力传递路径上实施水力压裂,在指定的区域制造出一定空间形态的水压裂缝网,形成压裂弱结构体,实现区域范围内的应力转移,从而降低巷道区域范围内的应力,控制巷道的围岩稳定性的控制技术,并通过理论分析及现场工程验证等方式,揭示了底板动压巷道压裂弱结构体应力转移的力学机制,建立了相应的力学模型,对压裂弱结构体的合理位置、范围等影响因素进行了求解。得出:(1)压裂弱结构体使局部应力场发生明显变化,出现应力升高区和应力降低区,应力降低区主要分布在弱结构体与采动应力连线的方向上,主要集中在一个拱形的范围内;由于膨胀效应,在与应力来源垂直的方向上产生应力集中,出现应力升高区。(2)最大主应力变化幅度与压裂弱结构体的长轴长L、短轴长H、到巷道的距离P、与巷道连线的水平夹角β、压裂层的强度C及内摩擦角α、压裂的损伤变量D等有关。其中到巷道的距离P对卸压效果影响最大,损伤变量D对卸压效果影响最小。(3)采用提出的计算方法设计了淮北矿业集团袁店一矿的103运输集中巷的卸压方案,工程应用结果表明,底板动压巷道变形速率明显减缓,验证了底板强动压巷道压裂弱结构体应力转移模型的合理性。

飞机结构梁多轴铣削加工程序与工艺优化研究

为解决飞机结构梁铣削加工过程中容易产生变形的问题。针对飞机结构梁类的薄壁腔体难加工零件进行了加工工艺分析和流程设计,此类零件的毛坯残余应力是影响零件加工变形的重要因素,有效的应力释放可以提高零件的加工质量。对此利用UGNX软件进行了数控编程,并利用VERICUT软件进行仿真,以最大切削厚度为目标进行了切削参数优化,优化后的程序能够有效的提高加工效率,并且探讨了以保证加工质量目标的刀轨编程策略和方法,有效的解决了飞机结构梁铣削加工过程中产生变形的问题。

薄壁结构件毛坯去应力分析与铣削加工变形有限元模拟研究

薄壁件在航空航天领域应用广泛,其制造精度直接决定了装备的服役性能。然而,由于热处理的影响,导致薄壁件在加工之前存在残余应力。如果控制不当极易导致零件超差。因此,本文以7075铝合金板材为研究对象,分析了残余应力在板料淬火与预拉伸时产生的原理。进一步,采用有限元方法作为工具,对7075毛坯在淬火和预拉伸法过程中残余应力的产生进行了模拟。通过模拟发现,当毛坯件被拉伸约3%,塑性应变量约为2.4%时,淬火残余应力消除可达91.2%。在降低残余应力的基础上,本文建立了薄壁结构件铣削加工仿真模型,模拟了多因素耦合作用下的铣削加工变形,并通过铣削实验验证了仿真结果的正确性。

涡轮盘封严齿裂纹返修后的荧光渗透检测

某型航空发动机高压涡轮盘新件在第一次整机试验后的荧光渗透检测过程中,多次发现在其封严齿第二、三齿上存在多条裂纹迹痕显示。通过理化检验、测试试验、过程复查等方法准确确定了裂纹产生的原因和机理,为制定故障排除方案及改进裂纹返修后的荧光渗透检测工艺提供了理论依据,最终优化了该盘件荧光渗透检测复检的工艺流程。

倾斜工作面面向断层开采煤柱失稳机制及稳定性控制

以某矿面向断层开采的5302工作面为工程背景,模拟了工作面回采过程中断层及断层周围煤岩体垂直应力、塑性区及断层滑移演化规律,提出了断层煤柱的合理尺寸,并制定了卸压方案。研究结果表明:工作面回采期间断层及断层周围煤岩体受构造应力与采动应力叠加作用下应力高度集中,容易诱发冲击地压;微震、应力在线监测结果对比分析表明,制定的爆破断顶、钻孔卸压技术方案能够有效降低应力集中程度,避免工作面面向断层开采时诱发冲击危险。

沿空留巷密集钻孔切顶机理及关键参数确定方法

为实现密集钻孔切顶条件下沿空留巷顶板结构安全稳定,研究正常情况与密集钻孔条件下顶板岩层结构受力状况,基于岩石断裂理论和弹性理论分析回采前后顶板密集钻孔孔间围岩受力分布及其破断过程,明确密集钻孔切顶机理及相邻钻孔的孔间集中应力相互作用机制,推导工作面端头弧形三角板结构巷道侧边界密集钻孔孔间围岩的拉剪应力计算公式。在此基础上,分析不同参数对孔间围岩所受拉剪应力的影响作用,提出沿空留巷密集钻孔切顶关键参数确定方法。研究表明:密集钻孔主要通过回采前后钻孔周围应力条件改变来增加钻孔围岩拉剪应力集中程度,引起孔间裂隙扩张联通,形成切缝线破断关键岩层。回采前钻孔主要受水平挤压应力影响,回采后钻孔受力逐渐转变为采空区顶板回转下沉产生的拉剪应力为主,钻孔孔间围岩状态随之由孔间围岩弱化阶段过渡到孔壁裂纹成形阶段,再转变为孔间围岩破断阶段。密集钻孔孔间围岩所受拉剪应力大小主要取决于关键岩层厚度及钻孔孔径与孔间距之比,与钻孔高度及间距成负相关,与角度及直径正相关。据此提出了密集钻孔关键参数确定方法,并根据龙滩矿3124 N工作面坚硬顶板条件设计了密集钻孔切顶留巷方案,确定钻孔长度为8.3 m,角度为15°,钻孔直径为48 mm,间距为500 mm。留巷后巷道顶帮变形可控且整体稳定性较好,由此可证明密集钻孔布置参数较为合理,密集钻孔关键参数确定方法有效可行。

超远距离下组煤层超前开采覆岩应力及裂隙演化规律研究

为探究平煤股份八矿超远距离下组煤层超前开采对上覆煤岩层的影响,采用相似材料模拟实验分析超远距离下组煤层超前开采上覆煤岩层裂隙及应力演化规律,并进行现场验证。研究结果表明:超远距离下组煤层超前开采条件下,随工作面推进,上覆煤岩层裂隙率呈先上升后平稳的趋势,当工作面从187 m推进至272 m,裂隙发育最快;超远距离下组煤层超前开采对上覆煤岩层有卸压效果,但与常规情况下相比卸压滞后距离较大;上覆岩层卸压比戊组煤层大;通过现场验证发现,随工作面推进,矿压呈先上升再下降后稳定的趋势,并将工作面区域分为未干扰区、应力集中区、卸压区和稳定区。研究结论可为平煤矿区远距离下组煤层超前开采、上组煤层工作面瓦斯防治和采区工作面采掘部署提供参考。

低温胁迫后紫花苜蓿叶片光合作用的恢复特性研究

为探究低温解除后苜蓿光合作用恢复过程中的限制位点,以‘新牧4号’和‘甘农5号’2个品种紫花苜蓿为材料,测定其低温胁迫及恢复过程中苜蓿叶片光合活性的变化。结果表明,低温胁迫下2个苜蓿品种叶片叶绿素含量、净光合速率以及光系统Ⅱ(photosystemⅡ,PSⅡ)活性显著下降,非光化学淬灭系数(nonphotochemical quenching factor,NPQ)显著上升,但对光系统Ⅰ(photosystemⅠ,PSⅠ)的活性无显著影响;其中,‘甘农5号’叶绿素对低温更敏感,含量下降较多。室温恢复72 h后,2个品种苜蓿叶片PSⅡ的活性及净光合速率都有上升但均未恢复至处理前水平;NPQ缓慢下降至处理前水平,‘甘农5号’NPQ较‘新牧4号’更高,表明在恢复过程中仍有过剩光能需通过NPQ消耗。苜蓿叶片的电子传递链在低温下受抑制显著,恢复72 h后PSⅡ受体侧活性基本恢复至处理前,而PSⅡ供体侧活性显著下降。2个品种苜蓿单位反应中心捕获的用于电子传递的能量(energy captured by unit reaction center for electron transfer,ETO/RC)和单位反应中心捕获的用于还原QA的能量(energy captured by the unit reaction center for reducing QA,TRO/RC)在低温处理72 h后显著下降,解除低温后恢复至处理前水平,且2个品种无显著差异;2个苜蓿品种单位反应中心耗散掉的能量(energy dissipated by the unit reaction center,DIO/RC)未恢复至处理前水平,且‘甘农5号’在恢复72 h后DIO/RC显著升高。综上,低温胁迫显著伤害紫花苜蓿叶片光合机构,降低了光合速率,光合速率未恢复到处理前与PSⅡ的活性显著相关,限制光合作用恢复的位点在其供体侧,非光化学淬灭是恢复24 h过剩光能的主要分配途径。

基于压力拱发展规律的隧道初次支护时机研究

本文依托济莱高铁宅科隧道工程,利用现场监测和FLAC 3D数值模拟的方法,基于隧道应力传递路径的改变探究压力拱形成机制和分布范围,得出隧道纵截面压力拱形态特征图,引入位移完成率衡量围岩的开挖扰动程度,建立位移完成率和应力释放率的对应关系,得到最优初次支护时机。研究结果表明:在隧道开挖过程中,上部围岩中应力逐渐偏转,围岩荷载逐渐向四周传递,最终达到新的应力平衡状态,即在隧道四周产生形成封闭环状应力现象的压力拱;隧道仰拱靠近拱脚部位围岩产生应力集中,在1.8 D(D为隧道截面宽度)范围内的围岩均参与成拱效应,承担隧道拱部上方的围岩荷载;对塑性区体积率进行计算与分析,认定70%~80%应力释放率较为缓慢,应作为最佳初期支护时间点;在开挖时隧道初期支护滞后于掌子面的距离宜控制在4.3~7.6 m。