An application of interacting shear flows theory: exact solution for unsteady oblique stagnation point flow

An analytical solution of the governing equations of the interacting shear flows for unsteady oblique stagnation point flow is obtained. It has the same form as that of the exact solution obtained from the complete NS equations and physical analysis and relevant discussions are then presented.

Microstructural evolution of 2519-T87 aluminum alloy obliquely impacted by projectile with velocity of 816 m/s

Target made of 2519-T87 aluminum alloy was obliquely impacted by a projectile. Microstructural evolution around the crater was investigated by optical microscopy （OM）, transmission electron microscopy （TEM）, and electron backscattered diffraction （EBSD）. The micro-hardness distribution near the crater after impact was studied. The results indicate that at the entering stage, the amount of adiabatic shear band （ASB） is the most, and the precipitates are as fine as those of the target material; the micro-hardness is higher than that at the other stages. At the stable-running stage, the amount of ASB reduces as the micro-bands increase; the precipitates tend to coarsen, which leads to the decrease of the micro-hardness. At the leaving stage, there is a large amount of micro-bands; the precipitates are refined, and the micro-hardness is higher than that at the stable-running stage. The difference in the micro-hardness of the impact stages is due to work hardening and precipitate coarsening, which is caused by adiabatic temperature rise in the alloy.

Oblique perforation of thick metallic plates by rigid projectiles

Oblique perforation of thick metallic plates by rigid projectiles with various nose shapes is studied in this paper. Two perforation mechanisms, i.e., the hole enlargement for a sharp projectile nose and the plugging formation for a blunt projectile nose, are considered in the proposed analytical model. It is shown that the perforation of a thick plate is dominated by several non-dimensional numbers, i.e., the impact function, the geometry function of projectile, the non-dimensional thickness of target and the impact obliquity. Explicit formulae are obtained to predict the ballistic limit, residual velocity and directional change for the oblique perforation of thick metallic plates. The proposed model is able to predict the critical condition for the occurrence of ricochet. The proposed model is validated by comparing the predictions with other existing models and independent experimental data.

Studies on the Coefficient of Friction During the Oblique Impact of a Hard Sphere Against a Ductile Solid Target

Following the original approach of Bowden and Tabor and introducing state variables, an effective friction coefficient μ_e for solid particle erosion is defined as a combination of shearing term and ploughing term. In the case of continuous sliding, based on considering the interaction between asperities under certain condition, it is indicated that during the oblique impact of a hardened steel sphere against a mild steel target, a possible value of μ_e is 0.05, which was chosen in all of the calculations by Hutchings for consistency with both experiments and calculations. In the case of continuous ploughing, it is shown that the value of μ_e is a function of the impact process and the initial impact angle and is greater than 0.05 on an average for Hutchings' experiments. It is suggested that the variation of sliding, rolling and ploughing state at each instant in the impact process makes “the coefficient of friction” equal to 0.05 for Hutchings' experiments, and in general, makes the effective friction coefficient during particle impact on metal far less than the friction coefficient during simple continuous sliding on an average.

Exposed Cross-section of the Archaean Lower Crustin the Shanxi-Hebei-Inner Mongolia Border Region:Problems and Prospects

The Archaean lower crust represented by granulite facies rocks, which is rare in China, is found to be exposed in the Shanxi-Hebei-Inner Mongolia border region. Studies of the regional structure and deformation and metamorphism of the region indicate that there occurred at least two phases of deformation and metamorphism in the region. Early-phase nearly E-W-directed deformational structure is well preserved in the Zhangjiakou-Xuanhua area. Observations of the features of the geological structure from north to south (in the Hengshan metamorphic terrain) have revealed a possible exposed cross-section through the Archaean lower crust. The structure was superimposed by a NE-SW-trending high-temperature ductile shear zone in the Datong area in the late phase, thus reworking the Archaean sequence.

多连杆式下斜刃横切剪剪切力数值分析

针对多连杆式下斜刃横切剪剪切力求解问题,采用有限单元法建立了数值求解模型。用装配后的实物进行了剪切实验,将数值解和实验解、文献解进行对比,三者结果之间比较吻合,验证了数值求解模型合理性。对不同带材厚度h、剪刃侧向间隙Δ、下剪刃斜度tanα、剪切液压缸伸出速度v及上下剪刃磨损量ω下的横切剪剪切力分布规律进行了归纳。分析结果表明,下剪刃磨损对剪切力的分布影响大于上剪刃的磨损,剪切厚度为6mm的带材的最佳剪刃侧向间隙Δ可取为(0.4±0.1)mm、下剪刃斜度tanα可取为1/25、剪切液压缸伸出速度可取为(300±50)mm/s。提出了横切剪在设计、选型、电气调试以及实际使用过程中的一些建议。

SV波斜入射下海底沉管隧道地震响应研究

为避免近场斜入射地震波对海底沉管隧道造成灾难性后果,对沉管隧道及其剪力键在斜入射地震作用下的动力响应规律进行深入研究。首先,基于时域有限元方法并结合黏弹性人工边界,将地震波转换为模型边界节点的等效节点力,建立基于波动理论的三维平面SV波斜入射方法,并采用半空间算例验证该方法的准确性;然后,在该地震波输入方法的基础上,利用ABAQUS软件建立土体-沉管隧道节段三维精细化有限元模型,研究地震SV波斜入射作用下不同入射角度对沉管隧道及其剪力键动力响应的影响。研究结果表明:1)当SV波入射角接近临界角时,斜入射对隧道竖向和纵向响应达到最大值,水平响应与入射角呈反比关系;2)斜入射会使结构中对称部位产生非对称剪力,剪力键的剪力承担比也发生改变;3)剪力键根部易产生拉伸裂缝,端角也可能因应力集中而产生局部破坏。

弯折波导杆的超声斜入射方法

波导杆技术是一种有效的超声辅助检测方法,在提升高温关键承压设备安全运行方面具有重要作用。现有的波导换能器因直入式发射声波,常被用来在线监测壁厚的腐蚀进程,难以对指定方向的缺陷进行有效检测。为了解决这个难题,基于斯涅耳定理以及导波的频散特性提出了一种弯折结构的波导杆来实现超声斜入射。首先分析了弯折波导杆中水平剪切波的传播特性,探究了波导杆的厚度、弯折角度对杆中声波传播的影响规律;然后,进一步研究了弯折波导杆在半无限空间内的声束指向性;最后通过一对弯折波导杆在线检测结构内部缺陷的试验证明了波导超声斜入射的应用价值。研究结果为基于斜入射技术的波导超声在线监测提供了坚实的理论基础。

右江断裂带旧州—泽屯小段的地貌与第四纪活动图像

为探讨右江断裂带百色以西段北支旧州—泽屯小段的第四纪活动特征,从右江上游的乐里河、澄碧河流域的构造地貌研究入手,首先对两条河流开展遥感地质解译,利用河流地貌与断层活动的响应关系获取断层的可能部位,对断层活动可能出露的部位开展路线地质地貌调查并进行验证,试图勾勒出该小段断裂带的第四纪活动图像,最后讨论了该小段断裂带的第四纪活动的成熟度。遥感地质解译和野外调查的结果显示:旧州—泽屯小段断裂带的第四纪活动图像与构造物理实验中的R剪切断层发育阶段图像相似,其成熟度低。这可能是该小段断裂带至今缺乏5.0级以上的高震级地震记录的原因之一。

粘层乳化沥青层间抗剪性能及其评价方法研究

为解决路面养护工程中超薄罩面层与原始路面间易出现剪切破坏的问题,选取三种乳化沥青通过斜剪试验模拟路面在车辆荷载下的剪切破坏。结果表明,温度升高会导致乳化沥青层间抗剪强度下降;面层混合料集料粒径增大与沥青量增多会导致层间抗剪强度增加;不同乳化沥青自身性质差异会导致层间抗剪强度不同,较SBS乳化沥青与普通乳化沥青,橡胶乳化沥青粘结性能最好。对比完整车辙板与复合车辙板的抗剪强度,复合路面抗剪强度较完整路面会发生不同程度的下降,其中无粘层油的空白复合车辙板下降程度最大,抗剪强度仅有完整路面的64.37%。通过洒布粘层乳化沥青可以使层间抗剪强度提高,其中橡胶乳化沥青可达到完整路面抗剪强度的75.85%。

超大直径螺旋埋弧焊管管端火焰切割平头机构的应用

为解决超大直径螺旋埋弧焊管管端坡口尺寸精度要求,对钢管管端坡口加工尺寸精度的影响因素进行了分析。通过对制管过程中机械平头、等离子切割、火焰切割等钢管切割方式的优缺点比较,提出了采用火焰切割平头工艺对管端坡口加工的改进方案。实际应用表明,管端火焰切割过程的稳定性、连续性,以及平头效率和坡口加工精度都有了明显的提高,管端坡口加工质量完全满足相关标准要求。

Bilateral shear strength of rectangular frame column based on simplified space truss-arch model

To investigate the bilateral shear strength of rectangular frame column subjected to oblique horizontal load, we presented a simplified space truss-arch model developed from unilateral truss-arch model. Main parameters in the new model were the cross-sectional area, transverse reinforcement raito, axial load, and material strength of the column. The reduction coefficient of concrete sterength owing to the severe cracking of column was also introduced in the model. Finally, 14 specimens under oblique horizontal load were tested to verified the feasibility and applicability of the space truss-arch model.

空气耦合超声斜入射法检测固体火箭发动机脱粘缺陷及成像技术研究

为实现固体火箭发动机复合材料壳体粘接结构的非接触在役检测,该文采用空气耦合超声斜入射反射法进行研究。构建空气耦合超声斜入射检测系统,根据理论和实验确定有效的入射角范围并得出最佳入射角度,使用不同频率的探头在最佳入射角度下进行斜入射横波法反射法C扫描成像,最后用图像处理方法对缺陷进行定量表征,并与穿透法C扫描结果进行对比。结果表明:当遇到缺陷时,信号幅值会增大;两种检测频率下,12°为最佳入射角,且频率越大,信号的衰减越大;使用420 kHz探头检测时获得的C扫描图像质量高于250 kHz。通过混合滤波、改进的区域生长图像分割、Canny算子边缘提取以及形态学平滑处理和细化等方法,有效提取缺陷边缘,可实现缺陷的定量表征,420 kHz探头定量精度明显高于250 kHz,且缺陷尺寸越大,该方法结果与穿透法结果越吻合。

Positive and negative shear lag behaviors of composite twin-girder decks with varying cross-section

In steel-concrete composite twin-girder decks, wide concrete slab would undergo significant shear lag warping effect, including positive and negative. Some researchers have investigated the positive shear lag of composite decks by means of one-dimensional line model, while the studies on the negative shear lag have not yet been reported until now. In this study, a new one-dimensional analytical model of composite twin-girder decks is first proposed based on the model proposed by Dezi et al. Besides slab shear lag effect and partial connection at slab-girder interface which have been included in the model of Dezi et al., the particularity of the proposed model relies on its ability to account for variation characteristic of cross-section. Verification of the analytical model is later conducted through comparison of results from the analytical analysis and elaborate FE analysis for a simply supported composite deck with increasing depth and a two-span continuous one with decreasing depth. Finally, three kinds of structural forms of composite twin-girder decks, including cantilever, simply supported and continuous decks, are selected to carry out the analysis of positive and negative shear lag behaviors by means of the analytical model. The influences of cross-sectional variation characteristic and load type on positive and negative shear lag behaviors are mainly investigated. Additionally, a new definition on effective width for considering simultaneously positive and negative shear lag behaviors is proposed. The results from the proposed analytical model and EC4 specification are compared to provide suggestions for designers and checkers. In this study, the proposed analytical model can provide a powerful numerical tool for researchers to conduct the further investigation, and the analysis on shear lag and effective width can assist in design analysis of composite twin-girder decks.

钢管混凝土框架-斜向槽钢加劲钢板抗震性能

地震来临迅速且破坏面极强,对于人类的危害无疑是巨大的,严重伤害的生命和财产安全,且我国处于地震频繁带,之前发生的唐山大地震和汶川地震等给我国带来了严重的创伤,这使得提高结构的抗震性能变得重中之重。通过ABAQUS建立9个分别为框架和剪力墙四边连接、三边连接、两边连接的单跨九层方钢管混凝土框架-斜向槽钢加劲钢板墙模型,这三种钢板墙结构分别在EI-centro波、James波、人工波三种地震波作用下进行时程分析,分别得出三种钢板墙结构的基底剪力、层间位移、顶点加速度力学性能并对比分析。结果表明:四边连接型钢板墙结构的基底剪力、层间位移比其他两种结构都小,其整体抗震性能总体要优于三边连接型和两边连接型钢板墙结构。四边连接型刚板墙抗震性能更好。

某燃煤电厂除尘器结构的可靠性鉴定

随着国家环保力度的不断加大,除尘器在电力、冶金、有色、石化等工业领域得到广泛应用。随着除尘器的大量使用,相继出现一些问题,甚至造成严重的事故,影响企业生产。据统计,已经发生过多起除尘器灰斗掉落、立柱压弯、墙板吸瘪等事故,尤其是近两年接连发生的多起电除尘器整体坍塌事故,造成重大人员伤亡。基于某实际工程案例,对某电厂除尘器结构进行可靠性鉴定,分析该电厂除尘器结构混凝土支架梁开裂原因并给出处理建议。通过现场检测及计算分析,得出该除尘器底部混凝土支架梁端部出现斜向剪切裂缝是由于壳体柱单肢支承于框架梁上,在除尘器负压工况下,该梁在壳体柱肢作用点处承受较大集中荷载作用,造成抗剪承载力不足,导致梁端部出现斜向剪切裂缝。该裂缝呈脆性破坏特征,存在较大安全隐患,应立即采取加固处理措施,并给出了相应的处理建议。

一种工程机械斜腹杆智能化转角冲剪方法及其冲剪生产线

斜腹杆是指塔吊、升降机等工程机械桁架上弦杆和下弦杆之间连接的杆件,防止杆与杆之间产生过大的挠度,增加桁架的整体刚度,使受力可以由整个桁架共同承担,并且可以承担与传递别的杆上以及节点处的荷载。由于焊接角度需求,其两端角度多变,长度也不一样。目前采用的多为手工冲剪成型,冲剪模具角度需人工调整,长度也是人工输送,自动化程度低,原材料利用率不高,产品的一致性差,劳动强度大,且杆件在冲剪过程中易开裂,不易发现。为解决这些问题,本文提供了一种斜腹杆智能化转角的冲剪方法及冲剪生产线。

型钢混凝土十形柱空间节点受剪机理及抗剪强度研究

为了研究型钢混凝土(SRC)十形柱空间节点在斜向荷载作用下的受剪机理、抗裂承载力及抗剪承载力,开发一套加载装置,采用柱端斜向加载方式对5个型钢混凝土十形柱空间节点进行低周反复荷载试验。观察节点核心区剪切面破坏形态,分析节点区两个主轴方向的箍筋、水平腹杆、钢腹板的应变分布规律及空间节点受剪机理和抗剪影响因素。结果表明:节点受剪面破坏为典型的剪切斜压黏结破坏;两主轴方向的箍筋、水平腹杆及钢腹板应变分布规律基本相同;空间节点受剪机理与型钢混凝土异形柱框架平面节点有着共性,但斜向荷载作用下,空间节点抗剪能力变弱,受力更为复杂。斜向加载角度对抗裂承载力影响不明显,而对抗剪承载力的影响应予以考虑,抗剪承载力与斜向荷载角度相关曲线近似于菱形。最后,基于各种配钢形式的SRC十形柱空间节点单向受剪下(沿工程轴)抗剪承载力计算方法的研究,提出在斜向荷载作用下节点抗裂承载力及抗剪承载力计算公式,计算结果与试验值吻合较好。

与冲蚀有关的粘着与犁沟摩擦系数

提出一种与冲击磨损有关的有效摩擦系数,它被定义为冲击过程中,每一瞬间的切向有效摩擦力与法向载荷之比.有效摩擦力被表示为剪切项与犁沟项之组合.剪切项依赖于剪切金属接合点的状态——滑移或滚动.犁沟项依赖于冲击物在冲击途中使靶材料发生移动的状态.此有效摩擦系数被应用于研究刚性球自由斜冲击延性靶问题.在忽略剪切项仅计及犁沟项的情况下,研究表明,Hutchings实验中的有效冲击摩擦系数是冲击过程与初始冲击角的函数,就时间平均而言,大于Hutchings为拟合计算与实验结果所取的摩擦系数常值0.05.有迹象表明,对于与固粒延性冲蚀有关的刚性球自由斜冲击延性靶问题,在一定条件下,有效摩擦系数主要由犁沟效应确定.

低周反复荷载作用下型钢混凝土异形柱的抗剪承载力分析

从剪应力分布入手,分析型钢混凝土(SRC)异形柱中翼缘对抗剪承载力的影响,得出翼缘对抗剪强度的提高系数。根据试验得到的各构件的破坏形态和破坏机理,分别推导各种配钢形式的SRC异形柱在正向荷载(沿工程轴)以及斜向荷载作用下剪切斜压和剪切黏结破坏的抗剪承载力计算公式,计算结果与试验实测值均吻合较好。理论分析和试验结果表明:T、L形柱的斜向抗剪强度大于正向,而十形柱的斜向抗剪强度小于正向。研究结果可供工程设计参考。