Multipass welding of thick section steels using autogenous CO2 laser welding and CO2 laser-MIG hybrid welding

Laser multipass welding techniques for thick section steels have been developed using a new type of UV combined narrow groove. The shape and sizes at the bottom of groove are determined by analyzing the plasma behavior using high speed photographic equipment. A stable autogenous CO2 laser welding process and greater penetration are generated at the root pass because of strong reduction of the plasma volume. According to the waveforms of welding current and arc voltage, and the interaction between the arc and the laser induced plasma, a suitable groove angle is obtained. Laser-double MIG hybrid welding process is studied and the optimum distances between the laser and two arcs are determined. By using autogenous CO2 laser welding, CO2 laser-MIG hybrid welding and laser-double MIG hybrid welding, 28 mm thick steel plates are welded with four passes. The welds produced are assessed by X-ray. No crack is found and there is only a small amount of pores. The experimental results show that the multipuss welding procedures proposed can realize the joining of thick section steels with high efficiency and good quality.

Effect of Single- versus Double-Layer Uterine Closure during Caesarean Section on Niche Formation and Menstrual Irregularity

Background: The myometrium at the location of the CS (caesarean section) scars, also known as residual myometrium thickness (RMT), is larger after a double-layer uterine closure procedure than following a single-layer one. It may lessen the formation of a niche that is the myometrium’s disruption at the location of the scar of the uterus. Gynecological manifestations, obstetric problems in a future pregnancy and birth, and maybe subfertility are linked to thin RMT and a niche. Objective: To ascertain if double-layer unlocked closure of the uterus is better than single-layer one in terms of post-menstrual spotting and niche development following a first CS. Patients and Methods: In this randomized clinical study, 287 patients were evaluated for qualifying. Of all eligible individuals, 57 patients were excluded from the study based on the inclusion criteria. Results: The variation in ages, gestational age, body mass index (BMI), and cesarean section indications between the two assigned groups is statistically insignificant. However, postmenstrual spotting was statistically significantly more common in single-layer group compared to in double-group. The current study revealed ultrasound findings suggestive of niche formation was statistically significantly more common in single-layer group compared to in double-layer group. Conclusion: As evident from the current study, it demonstrates the advantages of double-layer unlocked closure of the uterus over single-layer one in terms of post-menstrual spotting and niche development following first-time cs. Thus, we deduced that fewer niches are formed, and fewer menstrual spotting occurs in the presence of double unlocked layers closure. To ascertain the impact of uterus closure method on post-operative niche development and the risk of obstetrics and gynaecological problems, further prospective trials with extended follow-up periods are required.

Top coal flows in an excavation disturbed zone of high section top coal caving of an extremely steep and thick seam

与轻轻的剧降相比长墙的探穴，在为极其陡峭、厚的缝接的充分使机械化的最高煤的探穴的一张工作的脸的长度是短的，当它的水平节与增加高时生产。但是探穴比率是低的，在一些灾难的力量结果例如房顶下降，在煤气的累积导致的一张工作的脸和危险由最高的煤的本地、大的区域倒塌导致了它。在裂缝的发展以后并且煤身体变弱，极其陡峭的缝接的最高的煤(小粒的媒介) 的高、破节(超过 60 掳) 表演清除非线性的运动的特征。我们彻底地分析了地质的环境，挖掘的采矿条件扰乱了地区。从大规模 3D 为最高的煤鈥搘a ter 鈥揼a s 的模拟建模并且联合的一个物理实验基于结果，我们断定削弱的最高的煤能被认为是间断媒介。我们使用了一个粒子流动代码程序高比较并且分析移植进程和 30 m 的运动节在在 Weihuliang 煤矿极其陡峭的缝接变弱前后随着时间的过去超过煤。我们的模拟，实验和监视表演的结果水的那注射前并且预先切开爆炸改进探穴能力和对称的探穴，为大区域减轻空间动态倒塌超过煤，延长有害气体的迁居时间并且外面免除他们 mined 区域并且那么在采矿完成安全。

Section thickness-dependent tensile properties of squeeze cast magnesium alloy AM60

The development of alternative casting processes is essential for the high demand of light weight magnesium components to be used in the automotive industry,which often contain different section thicknesses. Squeeze casting with its inherent advantages has been approved for the capability of minimizing the gas porosity in magnesium alloys.For advanced engineering design of light magnesium automotive applications,it is critical to understand the effect of section thickness on mechanical properties of squeeze cast magnesium alloys.In this study,magnesium alloy AM60 with different section thicknesses of 6,10 and 20 mm squeeze cast under an applied pressure of 30 MPa was investigated.The prepared squeeze cast AM60 specimens were tensile tested at room termperature.The results indicate that the mechanical properties including yield strength(YS),ultimate tensile strength(UTS)and elongation(A)decrease with an increase in section thickness of squeeze cast AM60. The microstructure analysis shows that the improvement in the tensile behavior of squeeze cast AM60 is primarily attributed to the low-gas porosity level and fine grain strucuture which result from the variation of cooling rate of different section thickness.The numerical simulation(Magmasoft)was employed to determine the solidification rates of each step,and the simulated results show that the solidification rate of the alloy decreases with an increase in the section thickness.The computed solidification rates support the experimental observation on grain structural development.

“3-Section” Technology of Full-Dimension Mining in Flat Thick-Seam

To raise coal recovery ratio and solve the key problem of full-dimension mining, a new “3-section” technology of full-dimension mining is put forward in flat thick-seam according to the theory and mining practice. This technology is proved to be rational and feasible in rodway layout system of stagger arrangement.

Ultrasound Evaluation of Caesarean Scar of Prelabour and Labour Caesarean Sections: A Cross Sectional Analytical Study

Caesarean section is dramatically increased throughout the world in recent years. Rupture of the uterus is a devastating complication in trial of labour following previous Caesarean section. Evidence suggests that the size of the uterine scar and the residual myometrial thickness (RMT) are associated directly with the risk of uterine rupture and risk of dehiscence in subsequent deliveries. Impact of the prelabour and labour Cesarean section on the RMT has not been studied in detail. Objectives: To compare RMT, Caesarean scar defects and to evaluate the elasticity of the Caesarean scar between women who underwent prelabour and labour Caesarean sections. Methods: This was a Cross sectional analytical study. Women who underwent Caesarean section in their first pregnancy were recruited. Sample was stratified to prelabour and labour Caesarean section groups. Transvaginal ultrasound scan was performed six months following the Caesarean section. Dimensions of the uterus, uterine scar defect, RMT and elastosonography of the uterine scar were assessed. Results: A total of 240 postpartum women were analyzed. Uterine niche was detectable in 194 subjects. Prelabour CS group had demonstrated 91.7% (n = 110) scar defects (uterine niche) out of 120 cases and the rate among labour CS group was 70% (n = 84). There was a significant difference in the presence of uterine niche among 2 groups as Prelabour group was found to have more scar defects (p mm (SD 1.2) and 4.99 mm (SD 1.3) respectively and there was no significant difference (t = 0.38, p = 0.71). There was no significant difference between the dimensions of the uterine CS defects of the studied groups. Prelabour CS group had significantly higher Target strain [0.28 vs. 0.24 (t = 2.12, p = 0.04)] and significantly less strain ratio [1.45 vs. 1.55 (t -2.42, p = 0.04)] than labour CS group indicating a better scar in prelabour group. Conclusion: There was no significant difference in RMT and uterine scar defects between prelabour and labour Caesarean section groups. But prelabour Caesarean section scars were less stiff than labour Caesarean section scars. Further studies are warranted to elaborate on the association.

煤层采动巨厚松散层全断面监测及内部变形特征

开采沉陷是煤炭资源井工开发利用所面临的主要环境地质问题,尤其对于我国东部高潜水位矿区而言,巨厚松散层的移动变形控制与采动减损评价备受关注。为了研究巨厚松散层内部移动机制,明确其对地表移动变形影响,以淮南新集矿区某井田为研究区,通过采用分布式光纤与并行电法联合测试技术,构建超过600 m深度全断面钻孔监测系统,探究巨厚松散层变形特征和内部移动规律。全断面监测系统能够获取煤层采动区域巨厚松散层内部应变、位移信息及监测钻孔周围电阻率变化情况,量化地层监测断面松散层内部移动变形时空关系和渗流场变化数据,分析松散层内地层变形特征与发育形态。研究结果表明:多参量联合测试技术的应用,显著提高了对巨厚松散层移动变形的监测效率和变形定位的准确性,获得了工作面回采位置与松散层内部变形时空演变关系。并根据松散层变形特征,将采动影响过程划分为超前影响期、弱采动影响期、强采动影响期、采后沉稳期4个阶段,揭示了超前影响变形表现“台阶状”形态与采动影响期的“反向3字型”移动特征,同时分析了“反向3字型”移动模式的构成条件、影响因素。基于全断面监测数据,提出巨厚松散层变形多场可测信息量化评价方法,阐明了巨厚松散层在煤层开采过程中存在分层应力积累与释放的规律。研究内容为巨厚松散层内部移动变形的精细化监测分析提供重要的技术支持。全断面监测技术的应用,也可为采动损害过程监测与评价、矿山生态源头减损与减沉、沉陷区土地规划与复垦以及松散层内注浆改造等提供参考。

变厚截面材料激光穿透焊接自适应功率控制研究

激光焊接变厚截面板是实现汽车轻量化的有效举措,但在激光焊接过程中,因工艺不稳定易导致焊缝熔透状态不一致,工件焊接质量较差。由于激光功率易于控制且对熔深影响显著,因此从变厚截面板激光焊接过程中的功率控制需求入手,设计了功率控制软硬件系统,完成了功率控制平台的搭建;采用卷积神经网络对同轴图像采集系统获取的小孔穿透孔图像进行分类,依据穿透孔面积分为未熔透、适度熔透和过熔透,采用PID控制系统根据分类结果编码实时改变焊接功率以获得适度熔透状态;通过采用变截面板进行激光焊接功率自适应调控试验,获得了背部余高均匀的焊缝,验证了自适应功率监测和控制算法的有效性。

中等减振梯形轨枕轨道结构关键设计参数

为研究中等减振梯形轨枕轨道的动力学特性,采用直接刚度法建立了车辆-梯形轨枕轨道-隧道垂向耦合动力学模型,分析了减振垫垂向静刚度和梯形轨枕厚度对钢轨、轨枕和隧道动力响应的影响。结果表明:当减振垫静刚度在15~30 kN/mm时,减振效果均达到了中等减振要求,梯形轨枕减振垫的垂向静刚度可以根据环境敏感点的具体振动超标量进行选取;与普通整体道床相比,当梯形轨枕的板中减振垫垂向静刚度为25 kN/mm时,梯形轨枕在40 Hz以上的频率范围具有较好的减振效果;增加梯形轨枕厚度可以降低钢轨和轨枕的垂向位移,并通过增加参振质量的方式提高减振性能;当梯形轨枕厚度从0.15 m增至0.35 m时,钢轨垂向位移、轨枕垂向位移和隧道垂向加速度减小幅度达7.73%、和6.82%和18.18%;中等减振梯形轨枕轨道与普通整体道床衔接时,需要在梯形轨枕铺设段设置3块5.8 m过渡梯形轨枕,过渡梯形轨枕的减振垫静刚度应优先按照三级刚度过渡方案进行选取。

考虑全寿命周期的UHPC加固墩柱截面性能研究

针对某高速公路改扩建工程中墩柱的钢筋锈蚀、混凝土剥落露筋等病害以及部分伸缩墩的墩柱存在竖向裂缝、环向裂缝的问题,从全寿命周期角度考虑,采用UHPC增大截面加固法对墩柱塑性铰区域进行加固处理。在原有C40混凝土加固方案的基础上,设计考虑了UHPC强度(120 MPa和140 MPa)、UHPC加固层厚度(8 cm和10 cm)、墩柱设计直径(1.0 m、1.2 m、1.4 m和1.5 m)以及加固层是否配筋4种因素影响的加固方案。利用XTRACT软件分析了加固墩柱截面M-N曲线和M-φ曲线,研究了UHPC强度、加固层厚度、墩柱直径及加固层是否配筋对墩柱截面力学性能的影响。最后,从结构性能、耐久性、混凝土用量及美观性等方面综合对比分析了不同加固方案的加固效果。结果表明:UHPC强度对加固墩柱截面性能影响不大,墩柱承载力随着UHPC加固层厚度的增大而增大;对于不同设计直径的墩柱结构,加固10 cm厚度的UHPC与加固20 cm厚度的C40混凝土均可达到相同的承载能力水平;加固层配筋能够提高墩柱承载力,但8 cm厚UHPC配筋加固远不如10 cm厚UHPC加固效果。相较普通混凝土,利用UHPC加固能够减少或免除墩柱的维修,大幅降低养护成本,降低工程全寿命造价。

低频脉冲磁场慢性暴露对健康成年股四头肌收缩力及形态的影响

背景:目前已有关于低频脉冲磁场对骨骼肌结构形态影响研究发现了骨骼肌质量变化,但对接受慢性暴露后的形态变化未见相关研究。目的:观察低频脉冲磁场慢性暴露对腿部股四头肌最大自主收缩力与形态指标的影响,为使用该技术作为肌肉功能改善策略提供组织形态变化的参考依据。方法:招募普通健康受试者70名,随机分为接受磁场刺激的试验组与进行假治疗的对照组,每组35名,试验时长共计4周,试验组受试者每隔48 h进行1次15 min的低频脉冲磁刺激干预,对照组进行假治疗,干预间隔与时长与试验组一致,干预4周后观察不同组别受试者股四头肌最大自主收缩力值变化,利用B型超声影像作为评估手段,观察肌肉厚度、肌肉横截面积及羽状角指标的变化。结果与结论:①经过4周的低频脉冲磁场慢性暴露,68名受试者完成试验,试验组受试者股四头肌最大自主收缩力测试值显著增长(P=0.000),提升幅度显著高于对照组(P=0.008);②试验组受试者的肌肉形态3项指标均显著高于试验前测(P=0.000),而对照组肌肉厚度指标呈显著性下降(P=0.020),羽状角无显著性变化,横截面积显著性提升(P=0.000);③组间对比发现,试验组关于肌肉形态的肌肉厚度(P=0.012)、羽状角(P=0.003)及横截面积(P=0.049)3项指标均显著高于对照组;④上述数据证实,健康成年受试者经过4周的低频脉冲磁场慢性暴露,股四头肌的最大自主收缩力显著提升,同时观察到试验组的肌肉厚度、横截面积及羽状角3项肌肉形态指标的显著增长,对使用该技术作为肌肉改善的运动替代与医疗策略提供了肌组织形态改善的支持依据。

厚煤层大断面沿空巷道变形破坏机理及控制技术

针对沿空巷道受多次采动叠加影响极易发生变形失稳破坏的难题,以某矿1505W工作面厚煤层综放开采工作面为研究背景,综合采用理论分析、现场实测、数值模拟等多种研究方法探讨分析了沿空巷道围岩失稳破坏机制,并提出了围岩“浅部、深部、表层”控制方案。现场试验结果表明,提出的控制方案能够使巷道浅、深部围岩形成统一的整体,有效抑制了沿空巷道围岩变形,提高了巷道的稳定性。

超多车道高速公路超宽沥青路面水膜厚度分析

为解决道路通行能力的问题,改扩建工程通常采用扩宽通行段面的方法,超宽断面虽然提高了交通能力,但也增大了路面径流路径,增加了路面积水风险,而积水在路面形成水膜,降低路表与车胎的附着力,导致车辆发生水滑。高速公路,尤其是特殊路段,在不利天气条件等综合作用影响下的路面排水问题日益突出。依托南方某高速公路“六改十”改扩建工程项目,采用不同经验公式分别计算十车道及以上超多车道超宽断面路面水膜厚度,并分析不同因素对其的影响,为后续高速公路超宽断面的路面排水设计施工、研究提供参考。

降雨环境下公路超高段优化过渡设计方法研究

针对降雨环境下高等级公路超高过渡段行车安全的问题,对高等级公路超高过渡段的优化过渡设计方法进行研究。依托343国道泗阳来安至众兴段工程,采用纬地道路设计软件进行降雨模拟,对比分析三次曲线超高过渡方式与线性超高过渡方式分别在不同降雨条件、纵坡和过渡段长度等因素影响下的路面积水状况。结果表明:随着降雨强度和过渡段长度的增加,超高过渡段外侧路面积水情况将会加重,而纵坡坡度的增加,更有利于路面积水沿着纵坡方向排出,为此,尽量设计较大的纵坡坡度以及较短的过渡段长度更有利于超高过渡段路面的排水;纵坡和超高过渡段较小时路面最大水膜厚度的位置大多出现在最外侧车道,随着纵坡和超高过渡段的增加,路面最大水膜厚度位置逐渐向中央分隔带边缘线移动;一般而言,由于三次曲线超高过渡方式在横坡为零附近超高渐变率较大,更有利于路面排水,因此,该过渡方式的行车安全性优于线性超高过渡方式。

冷弯薄壁型钢纯弯构件截面分类

为研究冷弯薄壁卷边槽钢纯弯构件截面分类,基于试验数据验证后的有限元模型,对不同板件宽厚比下冷弯薄壁卷边槽钢纯弯构件进行了大量的参数分析。结果表明:抗弯承载力随翼缘与腹板宽厚比的减小而增大。在考虑翼缘与腹板相关作用的前提下,基于截面承载力得出板件截面宽厚比限值,提出了冷弯薄壁卷边槽钢纯弯构件截面分类方法。

南阳煤业大断面巷道支护方案设计及应用

针对南阳煤业3#煤层厚度大、回采巷道断面大、支护困难等问题,采用理论分析、数值模拟的方法,确定了合理的巷道支护方案,并在3302轨道巷进行现场试验。对3302轨道巷巷道围岩变形量、顶板离层量及锚杆受力进行实时监测。现场监测数据显示,巷道围岩变形量不大,顶板无离层、失稳风险,锚杆受力状态良好,可有效约束巷道围岩变形。

苏州中南中心底板大体积混凝土蓄水养护技术

苏州中南中心项目塔楼底板超厚、超大体积混凝土,在夏雨季进行浇筑,按照先浇筑先养护原则,采用挡水墙将底板面分为若干区域,分区域分阶段蓄水养护,具备良好的保温保湿效果,具有“密闭性、匀质性、统一性”的特点,同时可以抵抗恶劣天气的影响。

V形截面管充液压制圆角充填行为研究

基于力学分析,利用有限元模拟和充液压制成形实验研究了V形截面管圆角成形所需内压。在不同内压下对成形管材壁厚的变化进行了充液压制实验研究。并通过理论计算选择合适的实验参数,成形出符合要求的扭力梁结构件。结果表明:圆角半径越小,成形所需内压越大;V形截面管内圆角半径随着内压的增加而减小,外圆角半径随着内压的增加而增大;V形截面管壁厚增厚主要发生在上侧圆角区,减薄主要发生下圆角区,并且最大减薄发生在下圆角中心区。

深部大采高综采面区段煤柱聚能失稳机理和控制研究

针对深部厚硬顶板综采面区段煤柱失稳引起巷道大变形破坏等问题,以红庆河煤矿大采高区段煤柱为对象,采用理论分析、现场实测和数值模拟方法,对深部区段煤柱聚能失稳机理和煤柱失稳防控技术进行研究。得出如下结论:外部动载荷扰动、静载荷集中下煤柱发生能量的积聚,满足能量判据时煤柱发生弹性向塑性转换和能量转移,煤柱最终部分或全部失稳破坏。宽煤柱两边缘出现应力双峰值点,中心存在弹性核区,窄煤柱中心出现单应力峰值点无弹性区;提出了以煤柱合理宽度为核心,配合实施水力压裂围岩应力调控、大直径卸压钻孔和煤柱帮强力支护的防控技术体系,在红庆河煤矿成功应用。