Residual Mechanical Properties and Explosive Spalling Behavior of Ultra-High-Strength Concrete Exposed to High Temperature

In order to explore the characteristics of ultra-high-strength concrete exposed to high temperature,residual mechanical properties and explosive spalling behavior of ultra-high-strength concrete( UHSC) and high strength concrete( HSC) exposed to high temperatures ranging from 20 ℃ to 800 ℃ were determined. The microstructure of the specimens after exposure to elevated temperature was analyzed by means of scanning electron microscope( SEM) and mercury intrusion porosimetry( MIP). The residual compressive strengths of UHSC and HSC were first increased and then decreased as temperature increased. After exposure to 800 ℃,the compressive strengths of UHSC and HSC were 24. 2 % and 22. 3 % of their original strengths at 20 ℃,respectively. The residual splitting tensile strengths of both UHSC and HSC were consistently decreased with the temperature increasing and were approximately 20% of their original strengths after 800 ℃. However,the residual fracture energies of both concretes tended to ascend even at 600 ℃. The explosive spalling of UHSC was more serious than that of HSC. Moisture content of the specimens governs the explosive spalling of both concretes with a positive correlations,and it is more pronounced in UHSC. These results suggest that UHSC suffers a substantial loss in load-bearing capacity and is highly prone to explosive spalling due to high temperature. The changes in compressive strength are due to the changes in the density and the pore structure of concrete. The probability and severity of explosive spalling of UHSC are much higher than those of HSC due to the higher pore volume in HSC.

Microstructure and Mechanical Strength Predictive Modeling in Al 5052-Trapezoidal Grooved SS 304 Explosive Cladding

Aluminum alloy plates were explosively cladded to stainless steel plates with trapezoidal grooves on the mating surface.The process parameters viz,loading ratio,standoff distance and flyer plate thickness were varied based on the Taguchi analogy.The variation in the process parameters alters the kinetic energy dissipation and the deformation work performed at the interface,and dictates the interfacial wave amplitude and the mechanical strength of the dissimilar explosive clad.The optimum level of process parameters for attaining higher tensile and shear strength is computed by signal-to-noise ratio.Further,a mathematical model is developed for calculating tensile and shear strength of the clad,based on the regression analysis using statistical software Minitab-16,and the level of fit is determined by analysis of variance.

Effect of process parameters on microstructural and mechanical properties of Ti.SS 304L explosive cladding

The present work pertains to the study of microstructure and mechanical properties of explosively cladded commercially pure titanium(cpTi) with austenitic stainless steel(SS 304L) subjected to varied process parameters, viz., loading ratios(mass of explosive or mass of flyer plate) and preset angles. The microstructural study reveals the transformation from straight to wavy interface while increasing loading ratios. Vickers hardness increases with loading ratios, and the maximum hardness is witnessed in the closer proximity of collision interface. Ram tensile and shear strength of explosive claddings are higher than that of parent plates. While the base plate fails in impact test, the flyer plate is deformed, indicating good impact strength. Increased mass of claddings, due to oxide formation, is witnessed in corrosion tests, which confirms the superiority of explosive claddings in corrosive environment. Triaxial weldability window, an analytical estimation for Ti-SS 304L explosive claddings, is developed and correlated.

cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5-d]imidazole(BCHMX)as a part of explosive mixtures

cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5-d]imidazole(BCHMX) is a relatively available bicyclic nitramine in the present. Due to the high energetic content of its molecule(deformation of valence angles) it has heat of formation higher than β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane(β-HMX) by nearly three times. As a result, it has heat of explosion and relative explosive strength exceed that of β-HMX including their corresponding PBXs. However, penetration abilities of PBXs based on HMX are higher than those based on BCHMX. The relatively high initiation reactivity of BCHMX could be modified in a wide range by its incorporation in a suitable polymeric matrices. Regarding to the performance, coating of BCHMX crystals by 5 wt% Viton A produces the maximum performance while the mixture of BCHMX with polydimethylsiloxane(PDMS) seems to be the optimum composition for the development of PBX with low sensitivity.

Effect of energy content of the nitraminic plastic bonded explosives on their performance and sensitivity characteristics

Information about the forty nine nitraminic plastic bonded explosives(PBXs)and different nitramines were collected.Fillers of these PBXs are nitramines 1,3,5-trinitro-1,3,5-triazinane(RDX)and β-1,3,5,7-tetranitro-1,3,5-tetrazocane(β-HMX),cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole(bicyclo-HMX,BCHMX)and e-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane(e-HNIW,CL-20)which are bonded by polyfluoro-elastomers,polydimethyl-siloxane,poly-glycidyl azide,polyisobutylene,polystyrene-butadiene,poly-acrylonitrile-butadiene and hydroxyl-terminated polybutadiene in addition to a melt cast compositions based on 2,4,6-trinitrotoluene.For thirty two of these PBXs the relationships are specified and analyzed between heats of their combustion and relative explosive strengths;by means of these relationships it might be possible to estimate,which groupings in the macromolecule of binder could be liable to their primary fission in the PBXs initiation.Similarly,for forty two of these explosives,the relationships are described and analyzed between their enthalpies of formation and impact sensitivities;here is especially attention paid to PBXs filled by BCHMX.Specific rate constants from Vacuum Stability Test(VST)of four nitramines and twenty PBXs are introduced into relationships with their enthalpies of formation.Regarding to all the mentioned cases,increasing of energy content of the studied explosives leads to increase of the relative explosive strength or initiation reactivity,respectively.Exception with the opposite trend,the outputs of VST are for BCHMX,where in PBXs are matrices with the esteric plasticizers or the energetic poly-glycidyl azide.Admixture of RDX or HMX,respectively,into the BCHX PBXs gives ternary PBXs whose thermal stability,in the sense of applied VST,is higher comparing to the original binary explosives.

Enhancing the explosive characteristics of a Semtex explosive by involving admixtures of BCHMX and HMX

A well-known ternary plastic explosive,Czech Semtex 1H,contains a mixture of PETN and RDX softened by SBR.In this work,BCHMX was used to replace PETN in Semtex 1H to form Sem-BC+RDX.In addition,another mixture based on BCHMX and HMX as energetic fillers bonded by the polymeric matrix of Semtex 1H(Sem-BC+HMX)was studied.The particle size distribution of each individual explosive was determined to obtain the optimum mixing conditions.Friction and impact sensitivities were determined.The velocity of detonation was reported practically and the detonation properties were calculated by EXPLO5 code.The explosive strength of each sample was measured by the ballistic mortar test.The conclusion confirms that the velocity of detonation of Sem-BC+HMX was the highest in comparison with the prepared samples.Sem-BC+RDX has the least impact and frictions sensitivities.Sem-BC+RDX has higher detonation velocity,detonation properties and explosive strength than Semtex 1H.Addition of BCHMX in Semtex 1H as a replacement for PETN is the candidate to produce a high performance advanced Czech plastic explosive.

Behavior and mechanism of the bonding interface of 0Cr18Nig/16MnR by explosive welding

In order to investigate the bonding behavior and mechanism of the interface prepared by explosive welding, the bonding interfaces of 0 Crl 8Ni9/16MnR were observed and analyzed by means of optical microscope （OM） , scanning electron microscope （SEM） and electron probe microanalysis （ EPMA ）. It is found that the welding interfaces are wavy due to the wavy explosive loading. There are three kinds of bonding interfaces i. e. big wave, small wave and micro wave. There are a few seam defects and all elements contents are less than both of the base and .flyer plate in the transition zone of big wavy interface. Moreover, some ＂holes＂ result in the lowest bonding strength of big wavy interface nearby the interface in the base plate. All elements contents of the small wavy interface are between two metals, and there are few seam and hole defects, so it is the higher for the bonding strength of small wavy interface. There is no transition zone and defects in the micro wavy interface, so the interface is the best. To gain the high quality small and micro wavy bonding interface the explosive charge should be controlled.

Numerical and experimental investigation on aluminum 6061-Vgrooved stainless steel 304 explosive cladding

This study attempts to analyze the microstructure and interface behavior of aluminum 6061(Al 6061)-Vgrooved stainless steel(SS304)explosive cladding by numerical and experimental methods.Numerical simulation was performed by Smoothed Particle Hydrodynamics(SPH)technique,in ANSYS AUTODYN,and the results are correlated with experimental outcome.The machining of V-grooves on the base plate transform the melted layer formed in conventional cladding(without grooves on the base plate)into a smooth undulating interface,for a similar experimental condition.The flyer plate and collision velocities,observed in numerical simulation,are in good agreement to the analytical expectations.The pressure developed in the flyer plate is higher than the base plate and the maximum pressure is witnessed at the collision point irrespective of grooved base plate or otherwise.The temperature developed in the collision point of conventional explosive cladding exceeds the melting point of both the participant metals,whereas,it exceeds the melting point of aluminum alone,in case of V-grooved base plate cladding.The shear and impact strengths of the V-grooved base plate clads are higher than the conventional clads and the fracture surfaces exhibit mixed modes of fracture.

Effect of silicon carbide and wire-mesh reinforcements in dissimilar grade aluminium explosive clad composites

Aluminium composites are inevitable in the manufacture of aircraft structural elements owing to less weight,superior corrosion resistance and higher specific properties.These composites reduce the weight of the aircraft,improve the fuel efficiency and enhance the maintenance duration.This study proposes the development of dissimilar grade aluminium(aluminium 1100-aluminium 5052)composites with different reinforcement’s viz.,stainless steel wire-mesh,silicon carbide(SiC)powders and SiC powder interspersed wire-mesh,by explosive cladding technique.Wire-mesh enhances the friction and restricts the movement of flyer plate to craft a defect free clad,while SiC particles form a band on the interface.Highest strength is obtained when SiC powder interspersed wire mesh is employed as reinforcement.The dissimilar aluminium explosive clad with SiC particle reinforcement results in lower strength,which is higher than that of the weaker parent alloy and that of the conventional dissimilar aluminium explosive clads without any reinforcement.

Relief of Residual Stresses in 800 MPa Grade High Strength Steel Weldments by Explosion Treatment and its Effect on Mechanical Properties

爆炸处理技术在焊接的高强度钢手册连接的 800 MPa 等级在剩余压力的消除被使用了。表面上并且通过焊接的厚度的剩余压力被测量为同样焊接并且 explosion-treatedsample，在不同条件下面的焊接关节的机械性质也被测试。有一个剩余缺点的材料的破裂坚韧上的爆炸处理的 Theeffect 被打开排水量(货到付款) 测试的快克调查。结果证明爆炸处理能在焊接关节通过厚度减少不仅表面剩余压力而且剩余压力。在焊接关节的机械性质和一个剩余缺点上的爆炸处理的效果是不引人注目的。

Study on Mechanism of Explosive Spalling of ULC Castables During Rapid Drying

Inner vapor pressure and temperature of vulnerable explosive spalling positions in refractory castables during rapid drying were measured by embedding pressure transmitting pipes and thermocouples during casting. The measured vapor pressure, temperature, and tensile strength of the castables were analyzed and discussed. A hollow sphere shell model was used to analyze the stress induced by the vapor pressure based on the structure of refractory castables. The mechanism of refractory castables explosive spalling caused by vapor-induced pore split was proposed. By comparing the vapor-induced stress and the tensile strength of the castables, the explosive spalling mechanism was validated quantitatively.

我国城乡高中一、二年级学生体质健康测试状况的调查研究

背景目前有关高中生体质健康测试成绩的研究以各省、市内局部地区较为多见,多中心大样本量的全域研究甚少。各类学校在普遍开展线上与线下混合式教学时,势必延长了高中生本已较长的静坐时间。这种趋势是否对高中生的体质健康产生一定的影响,亟待开展全域范围的调查研究。目的调查并分析我国七大地区城乡高中一、二年级学生的体质健康测试成绩水平及相关影响因素,探索出高中一、二年级学生的体质健康水平均衡提升的赋能路径。方法采用分层随机整群抽样方法,于2019年1—3月在我国31个省(直辖市、自治区)七大地区(华东、华南、华北、华中、西北、西南、东北)高中学校按照市区县与乡镇村进行分层抽样,然后随机整群分别选取市区县高中学校和乡镇村高中学校各1所,共62所学校42523名在读的高一、高二年级学生进行调研,同时收集学生的体质健康测试成绩数据(BMI反映身体发育水平,肺活量反映身体功能,坐位体前屈反映躯体柔韧度,引体向上、50 m跑、立定跳远反映上下肢爆发力量水平,1 min仰卧起坐反映躯体核心力量水平,800 m跑、1000 m跑反映心肺耐力水平),并运用非参数检验及多元线性回归分析探讨体质健康测试成绩水平的影响因素。结果42523名高中生的中位年龄为16.0(16.0,17.0)岁;男生20074名(47.2%)、女生22449名(52.8%),市县区21725名(51.1%)、镇乡村20798名(48.9%)。七大地区高中生性别、城乡分布比较,差异有统计学意义(P<0.05)。七大地区高中男生各项体质健康测试成绩比较,差异均有统计学意义(P<0.05);各项体质健康测试成绩前三的地区如下:身高(华北>东北>华中)、体质量(东北>华北>华中)、BMI(华中>东北>华北)、肺活量(东北>华中>华南)、50 m跑(华南>华中>华东)、立定跳远(华南>华北>西北)、坐位体前屈(华南>西南>华中)、引体向上(华南>西南>西北)、1000 m跑(华南>华中>西南)。市县区高中男生的肺活量成绩高于镇乡村,50 m跑、立定跳远、坐位体前屈、引体向上、1000 m跑成绩低于镇乡村(P<0.001)。七大地区高中女生各项体质健康测试成绩比较,差异均有统计学意义(P<0.05);各项体质健康测试成绩前三的地区如下:身高(华北>东北>西北)、体质量(东北>华北>西北)、BMI(东北>华北>西北)、肺活量(东北>华南>华中)、50 m跑(华南>华中>华东)、立定跳远(华南>华北>华中)、坐位体前屈(东北>华中>华南)、1 min仰卧起坐(华北>华中>华东=西南)、800 m跑(东北>华中>华南)。市县区高中女生的身高、体质量、BMI成绩高于镇乡村,肺活量、50 m跑、立定跳远、坐位体前屈、1 min仰卧起坐、800 m跑成绩低于镇乡村(P<0.001)。多元线性回归分析结果显示,男生引体向上成绩与BMI、1000 m跑成绩呈负相关,与50 m跑、立定跳远、坐位体前屈成绩呈正相关(P<0.05),坐位体前屈为最主要的影响因素,1000 m跑次之;1000 m跑成绩与BMI、肺活量、引体向上成绩呈负相关,与50 m跑、立定跳远、坐位体前屈成绩呈正相关(P<0.05),引体向上为最主要的影响因素,坐位体前屈次之。女生1 min仰卧起坐成绩与BMI、肺活量、立定跳远、800 m跑成绩呈正相关,与50 m跑、坐位体前屈成绩呈负相关(P<0.05),BMI为最主要的影响因素,坐位体前屈次之;800 m跑成绩与BMI、50 m跑、坐位体前屈成绩呈负相关,与立定跳远、1 min仰卧起坐成绩呈正相关(P<0.05),坐位体前屈为最主要的影响因素,BMI次之。结论我国市县区高中一、二年级男生的身体发育水平与镇乡村相当,但市县区高中一、二年级女生的身体发育水平高于镇乡村女生。市县区高中一、二年级学生的上下肢爆发力量、躯体核心力量、心肺耐力水平均显著低于镇乡村。除身体发育水平以外,华南地区的高中一、二年级男生的体质健康各项测试成绩水平的优势十分明显。

下肢相对力量水平激活后增强效应对运动表现影响的Meta分析

目的:激活后增强效应对运动表现的影响特征主要是肌肉活动能力增强、肌肉力量产生速率提高等方面。文章通过Meta分析定量评价下肢相对力量水平激活后增强效应对冲刺速度、跳跃表现和动力学参数(峰值冲量、峰值功率、最大地面反作用力和力的生成速率等)的影响效果。方法:应用计算机检索中国知网、万方、Web of Science、PubMed和Medline数据库关于下肢相对力量水平诱导激活后增强效应的随机对照、随机交叉或明确按照下肢相对力量水平分组(非随机对照试验)的研究,各组干预方法主要以自由质量器械和快速伸缩复合练习等为措施,文献发表时间为各数据库建库至2023-08-05,使用EndNote软件管理文献,随机对照试验按照PEDro量表、非随机对照试验按照ROBINS-I 2.0标准进行文献质量评价,采用RevMan 5.4和Stata 15.0软件对所提取的数据进行发表偏倚评价、亚组分析及敏感性分析,并制作森林图进行Meta分析。结果:①最终纳入11篇文献,包括7项随机对照试验和4项非随机对照试验,共216名受试者,整体文献的方法学质量较高。②按照1次最大重复量/体质量(1RM/BM)>2为强壮组99人、1RM/BM≤2为普通组117人,均为男性受试者。③Meta分析结果显示,强壮组激活后增强效应对短跑表现的积极效果显著高于普通组(SMD=-1.34,95%CI:-1.74至-0.93,P<0.00001);强壮组激活后增强效应对垂直跳跃高度的影响与普通组相比差异无显著性意义(SMD=0.30,95%CI:-0.07-0.66,P=0.11);强壮组激活后增强效应对峰值冲量(SMD=-0.07,95%CI:-0.62-0.47,P=0.61)、峰值功率(SMD=0.21,95%CI:-0.29-0.72,P=0.12)、最大地面反作用力(SMD=0.31,95%CI:-0.20-0.81,P=0.16)及力的生成速率(SMD=0.36,95%CI:-0.11-0.82,P=0.39)的积极效果与普通组相比差异无显著性意义。结论:现有的试验证据表明,强壮组激活后增强效应能够显著提高短距离冲刺速度,下肢相对力量水平激活后增强效应对爆发性垂直跳跃高度、峰值冲量、峰值功率、最大地面反作用力以及力的生成速率等运动学和动力学参数指标的影响效果类似。

基于新型聚氨酯弹性体材料在PBX炸药载体中的应用

为提高高聚物粘结炸药(polymer bonded explosive,PBX)炸药载体的力学强度,在炸药的粘结剂体系中引入聚氨酯弹性材料进行聚醚/聚酯粘结剂高强度载体设计。通过调控聚氨酯弹性体制备过程中多元醇的比例和分子量、固化剂的种类,利用旋转流变仪和多功能万能材料试验机开展材料固化速率性能分析和固化后聚氨酯弹性体对端羟基聚丁二烯(hydroxyl-terminatedpolybutadiene,HTPB)粘结剂体系力学强度影响规律分析。结果表明:PCL_PTMG聚氨酯弹性体拉伸强度的大小与固化剂的固化速率相关;改变聚酯聚醚分子量对弹性体抗拉强度的影响不大;当聚酯聚醚的比例为4:1时,弹性体抗拉力学强度最优;聚氨酯弹性体增大了HTPB粘结剂体系强度。

高强灌浆料加固灌注桩桩头研究

加固的桩头承载能力对静载试验成功与否至关重要,常规做法是采用混凝土进行桩头加固,但周期较长,且有时效果不好。统计表明,用混凝土加固的试验桩桩头,压爆数量占试桩总破坏数量的20%左右,基于此采用了高强灌浆料代替混凝土进行桩头加固。设计了水泥基高强灌浆料的配合比,制作了三组试块,轴心抗压强度试验结果表明,该材料短期强度发挥较快,1、3、7 d的平均抗压强度可以达到35.3、51.5、68.5 MPa。大量现场试验证明该材料加固混凝土试验桩在技术上是可行的,且具有很大的时间优势。针对不同承载力灌注桩,给出了桩头加固形式和龄期的建议。

爆炸焊接制备铝-钛复合板工艺研究

开发了1060铝/TA2钛直接爆炸复合新工艺,研究装药量、间隙距离和垫板等参数对复合效果的影响。结果表明:装药量和布药方式对铝-钛板复合强度有明显影响,结合面剪切强度随装药量增多而先增加后降低,分析对比后确定了装药量、间隙距离和垫板形式;爆炸焊接时对6种工艺参数制备的铝-钛复合板结合性能进行分析对比,确定了适宜的焊接参数,进一步优化垫板缓冲层和阶梯布药方式,生产的大规格铝-钛复合板有效区结合率达到100%,批量生产合格,复合质量和结合强度优良,掌握了大规格铝钛直接爆炸复合的工艺技术。

爆炸冲击作用下不同材料箱型梁桥损伤分析

利用ANSYS/LS-DYNA有限元软件,采用三阶段耦合方法模拟了爆炸作用下某实际钢筋混凝土小箱梁桥局部毁伤与整体毁伤过程,得到了在35kg当量炸药下箱型梁桥关键构件的破坏模式与损伤机理,研究了爆炸作用下不同目标材料对箱型梁桥的损伤影响。基于靶板最大位移公式,得到了爆炸冲击作用下不同箱型梁桥材料强度与损伤Y向位移比值之间的联系。结果显示:当炸药当量为35 kg时,箱形梁桥整体未出现倒塌,顶板毁伤最为严重,出现贯穿损伤,混凝土剥落严重,出现椭圆形炸坑;腹板与顶板交界处出现裂缝,模拟过程印证了冲击波爆炸时先在表面形成环状向外扩散,随后水平扩散至翼缘板边缘再开始向下蔓延的理论;随着材料强度不断提高,箱型梁桥损伤面积不断减小,箱梁稳定性也逐渐提高。

钛-钢板材爆炸焊接工艺优化实验与数值模拟研究

设计了钛-钢板材的爆炸焊接工艺优化实验,分别对钛-钢板材的剪切强度及界面微观组织结构展开检测。实验结果表明,经过爆炸焊接处理后,钛-钢板材的剪切强度均达到了行业标准,SEM图像中两种材料的复合界面有明显的“象鼻”状凸起和旋涡,这对提高钛-钢板材结合强度有积极作用。利用LS-Dyna软件,构建钛-钢板材模型并展开数值模拟,仿真结果表明,适当增加装药量可使复板获得更快的运动速度,相应的塑性应变增加,当复板与基板间隔距离为6 mm、装药量为30 kg/m^(2)时,复合板材结合面的剪切强度最大。

超等长奥举动作在爆发力训练中的生物力学优势

通过运动生物力学实验探索超等长奥举动作变式在爆发力训练中的生物力学优势。招募10名大学生运动员作为研究对象,采集受试者在不同负荷下练习传统高抓、传统高翻、超等长高抓和超等长高翻时的运动生物力学数据,利用数理统计法和机器学习算法,比较不同动作的运动生物力学特征。结果发现中等相对负荷下,超等长高翻具有生物力学优势,但高相对负荷下超等长高抓具有生物力学优势;奥举动作及其变式的下肢动力学特征相似,但在中等和次最大强度爆发力负荷下进行爆发力训练时,超等长动作间的下肢关节动力学差异更小。结果说明,超等长奥举动作在爆发力训练中具有显著的生物力学优势,建议结合训练者的需求及技术,制定个性化训练计划。

组合力量训练对篮球运动员身体爆发力的影响研究

篮球是一项以力量作为基础的运动项目,现代高水平竞技篮球由于进攻时间的限制使得攻防转换的速度越来越快,各队不断强化“快”的意识和“快”的训练,使得比赛中各个环节的衔接也越来越快,快速逐渐成为篮球运动的核心和灵魂.运用分组对比、独立t检验、配对t检验的方法,旨在探究组合力量训练对篮球运动员身体爆发力的影响,同时为达到更好的训练成果,探索更为丰富的训练方式,找出有效提升运动员身体爆发力的方法.