Taylor冲击载荷作用下PBX炸药细观损伤模式及机理研究

空对地钻地弹在高速侵彻过程中,装药部的提前起爆严重影响到对攻击目标的毁伤作用,针对这个急迫需要解决的问题,对装药部(PBX炸药)在高g值载荷作用下的细观损伤模式及机理进行研究。基于一级轻气炮,应用激光测速系统监测实验试件击靶速度,由压电传感器采集实验试件应力状态,进而通过Taylor冲击加载方式对PBX炸药损伤形式进行实验研究。基于细观损伤理论,结合扫描电子显微镜(SEM)对其损伤模式进行分析,结果表明,在较小冲击载荷作用下,晶体颗粒表面与粘结剂之间的剪切脱粘细观损伤模式最先发生;随着冲击载荷能量的增加,产生了细观损伤裂纹,并不断沿应力薄弱路径急剧传播,且萌生新的损伤裂纹,裂纹传播错综复杂,进而导致颗粒破碎,发生穿晶断裂、粘结剂劈裂等细观损伤模式,从而导致该PBX炸药宏观损伤裂纹的出现。PBX炸药细观损伤理论对该PBX炸药细观损伤模式的预测结果与实验分析结果基本相符,该细观损伤理论为其细观损伤机理研究提供了重要依据。     

两次脉冲加载条件下炸药装药的安全性实验技术

为获得炸药装药在多次脉冲载荷条件下的安全性,基于大型落锤模拟加载装置,设计了两次脉冲实验装置,建立了两次脉冲载荷条件下炸药装药安全性实验方法。研究了CL-20基含铝炸药在两次脉冲载荷条件下的安全性。结果表明:所用的实验装置可以对CL-20基含铝炸药装药实现两次脉冲,实验原理可行。锤头高度为1.0 m时,炸药装药在两次脉冲载荷作用下未发生点火;锤头高度超过1.2 m后,炸药装药在第二次脉冲载荷作用时发生点火。     

侵彻单层靶时着靶姿态对装药损伤的影响规律研究

为研究着靶姿态对高速侵彻弹装药损伤的影响,依据实际战斗部的结构尺寸设计了小尺寸模型试验弹,在125 mm口径的滑膛炮发射平台上开展了试验弹以不同攻角斜侵彻单层钢靶试验。通过理论计算得到着靶姿态对侵彻过程能量损失的影响。利用CT扫描无损检测技术观测不同着靶姿态下试验弹内部的损伤情况。运用LS-DYNA对试验弹侵彻钢靶过程中装药的力学响应过程进行模拟计算。结果表明:在斜侵彻单层钢靶的过程中,着角一定时,能量损耗与攻角呈指数关系;试验弹的倾角越大,装药尾部受到的应力波拉伸压缩反复作用越明显,装药在侵彻过程中长度变化越大,更易出现深度裂纹、塌边等损伤;壳体外形变化会引起装药受到的压缩应力阻碍微裂纹的扩展和滑移,减少宏观损伤的出现。     

钢筋混凝土柱加载试验AE监测研究

利用声发射(Acoustic Emission,AE)技术分析动、静态加载下钢筋混凝土柱的断裂、损伤特性。用40mm/s,0.1mm/s两加载速率分别进行钢筋混凝土柱多维循环加载试验。据AE的b值理论捕捉宏观裂纹开始拓展时刻荷载状况,提出用定义宏观开裂发生荷载与极限荷载之比评估钢筋混凝土结构损伤;并对比分析动、静态加载实验中钢筋混凝土柱宏观裂纹初始荷载状况与损伤增长速率。结果表明,利用b值理论即声发射信号幅值分布变化,能捕捉到钢筋混凝土柱裂纹宏观拓展时刻;与静态加载相比动态加载时宏观裂纹的形成所需荷载更小,动态加载更易导致宏观裂纹形成;AE事件累计时间参数能清晰反映钢筋混凝土柱的损伤增长速率,且加载速率高的构件损伤速率高于加载速率低的构件,高加载速率更易导致、加剧结构损伤。     

装药落锤冲击实验载荷特性研究

在装药发射安全性试验中,只有落锤的冲击载荷与膛压曲线较为相近时,落锤冲击试验结果才有意义。落锤冲击载荷特性与多种因素有关,通过对各种因素的调整,使落锤冲击载荷与膛压曲线吻合是落锤法进行装药发射安全性试验的前提,也具有一定难度。采用ANSYS/LS-DYNA非线性有限元软件对落锤冲击载荷作用下炸药装药内部压力的变化过程进行数值模拟,通过改变落锤的高度、落锤的质量以及炸药装药的高度,来研究炸药装药内部的动态响应特征(压力变化的过程)。模拟实验的结果表明:落锤的高度、落锤的质量以及炸药装药的高度对炸药装药内部压力都有影响;落锤的质量和炸药装药高度对压力脉冲作用时间宽度有影响,而落锤的高度对压力脉冲作用时间没影响。     

水耦合装药不耦合系数对爆破效果的影响研究

为了研究水耦合装药条件下不同不耦合系数对爆破效果的影响,采用透明均匀、直径250 mm、高200 mm的圆柱体PMMA材料作为试件,DDNP炸药用于施加爆破载荷,试验中炸药量固定为40 mg,同时使用水耦合装药结构,通过不同的孔径和装药直径来改变试验的不耦合系数,通过比较爆后试件内部裂纹数量及分布、粉碎区大小等情况来分析三种不同的不耦合系数(1.4、2.0、2.67)对爆破效果的影响.通过对比发现:适当增大水耦合装药的不耦合系数可以增多裂纹数量,使裂纹分布更加均匀,增大裂隙区,减小破碎区直径.并发现存在一个最佳不耦合系数使得爆破效果达到最佳,在3个不耦合系数中,最佳不耦合系数为2.67.试验利用PMMA材料的透明均匀特性对爆破断裂行为进行直观的观察,试验结果更加可靠,且对脆性材料普遍适用.     

成型温度对PBX装药内部质量及性能的影响

针对压制成型的PBX炸药装药，选择CT无损检测、巴西实验和扫描电镜检测等技术，对比研究了室温和加热两种温度下压制成型的炸药装药内部质量、静态力学性能和细观破坏形式。结果表明，加热压制有利于改善炸药装药的内部质量，可避免产生初始损伤，且提高了装药的力学性能。细观尺度上，室温压制成型的装药主要发生界面脱黏破坏，加热压制成型装药的主要破坏形式是穿晶断裂。     

腐蚀环境作用下失效的失效分析(续)

氢损伤指在金属中发生的一些过程，这些过程导致金属的承载能力因氢的出现而下降。氢损伤可以按照不同方式分类。按照氢损伤敏感性与应变速度的关系可分为两大类。第一类氢损伤的敏感性随应变速度的增加而增加，其本质是在加载前材料内部已存在某种裂纹源，故加载后在应力作用下加快了裂纹的形成和扩展。第二类氢损伤的敏感性随应变速度的增加而降低，其本质是加载前材料内部并不存在裂纹源，加载后由于应力与氢的交互作用逐渐形成裂纹源，最终导致材料的脆性断裂。     

一种DNAN基熔铸炸药压滤装药工艺安全性分析

为确保混合炸药在压滤装药工艺过程中的安全性,通过工艺过程安全性分析,获得了工艺安全性风险因素及其分类;利用试验测试和数值仿真手段,对一种DNAN基熔铸混合炸药(MCX-D)的本质安全性、相容性、机械和热刺激等装药工艺安全性影响因素进行了分析与研究。结果表明,炸药本质上是安全的,压滤工艺过程中组分变化和热损伤导致炸药本身感度的升高有限(机械感度≤40%),符合使用要求;装药在温度和压力双重作用下的内部温升仅为0.3℃左右,不存在热爆炸的可能性。由此证明DNAN基熔铸炸药压滤装药工艺是安全可靠的。     

二维C/SiC复合材料在冲击拉伸下的损伤过程

利用分离式霍普金森拉杆实验装置(SHTB)和超高速照相机,对二维C/SiC复合材料进行了冲击拉伸力学性能实验研究,同时结合其宏观力学行为,分析了在冲击拉伸载荷作用下的损伤破坏过程。结果表明:材料的应力-应变曲线呈明显的非线性特征,其内部损伤破坏和裂纹扩展过程分为四个阶段:损伤积累于第一阶段,裂纹起源于第二阶段,屈服失效于第三个阶段,快速扩展于第四个阶段。     

锥角参数对单向聚能药柱爆破破岩效果的影响

为研究聚能穴锥角参数对爆炸应力和岩石损伤破裂范围的影响,以获得最优的聚能穴参数,从而达到最佳的破岩效果,利用有限元模拟软件LS DYNA建立了6种锥角参数下的单向聚能药柱模型。锥角的深度为15 mm,6种锥角高度分别为10、12、14、16、18 mm和20 mm。研究了岩石裂纹扩展的影响规律,测得聚能方向与非聚能方向上不同位置的有效应力,得到不同锥角参数对应的岩石单元的最大破坏距离。结果表明:聚能锥角会对爆破产生定向作用,特别是对岩石破碎和拉伸裂纹所带来的破岩效果影响明显;当锥角高度为10 mm时,距炮孔25 cm测点处聚能方向上的有效应力比非聚能方向同样距离处高110.8 MPa,同时,聚能方向上单元损伤比要比非聚能方向高21%,聚能效果最佳;随着锥角高度逐渐增大,聚能方向上岩石裂纹逐渐减少,裂纹分叉减少,单元破坏最大距离可达108.1 cm,并且呈下降趋势。     

Microscopic fatigue processes in a plain-weave glass-fibre composite

This paper focuses on the microscopic damage and progressive failure of a composite reinforced by plain-weave glass cloth under tensile fatigue loading. The fatigue process was divided into three stages like that of multi-directional laminates. It was found that the internal damage at each stage (matrix cracks, debonds in the weft, successive debonds in the warp and ‘metadelaminations’ between warps and wefts) occurred near the cross-over point of the fabric. The modulus decay mechanism was explained by considering the progression of this internal damage. From the end of the first stage to the beginning of the middle stage, a characteristic damage state (CDS) (called a ‘meta-CDS’) was observed. It was found that woven composites have a unit area of damage accumulation (called a ‘unit cell’) and the damage of each unit cell and its distribution control the total fatigue damage of the material.     

三维五向编织复合材料渐进损伤分析的数值方法

基于连续损伤理论, 推导了含损伤裂纹的正交各向异性材料的应力-应变关系。建立了考虑界面脱粘破坏的三维五向编织复合材料细观体胞模型, 并将有限元网格尺寸和单元裂纹尺寸引入损伤演化方程。采用Hashin准则和von-Mises准则分别判断纱线与基体的初始损伤, 结合Eshelby-Mori-Tanaka方法确定材料的刚度退化系数。利用ANSYS有限元软件对材料进行渐进损伤分析, 得到了材料在单向拉伸作用下的应力-应变曲线和极限强度。计算结果表明, 轴纱为材料的主要承力部分, 小编织角材料的破坏模式主要为纱线的拉伸断裂, 界面破坏情况较为严重。模拟计算结果与实验结果吻合较好。     

Crack coalescence morphology in rock-like material under compression

This paper uses peridynamic simulations to determine the extent of coalescing damage and identify the underlying causes. The basic crack types and crack coalescence patterns in specimens with a flaw pair under uniaxial compression are systematically investigated. Various crack types including horsetail cracks, anti-wing cracks, and tensile wing cracks are successfully observed and the coalescence sequences are identified. By varying angles, six crack coalescence categories with respect to the overlapping ratios provide insightful information of different crack growths and indicate various cracking modes underlying various coalescence patterns. The arrangement of the flaw pair strongly influences the crack initiation position and trajectories, allowing for different coalescence morphologies. Coalescence formed by two internal tensile wing cracks, or transfixion, shows unbroken crack segments with a further loading, along with growing shear cracks until failure. In contrast, after the coalescence is formed through two horsetail cracks, the interior of the rhombic shape gets deformed with further loading. The peridynamic code adopted in this research can provide realistic simulation results and help researchers to conduct expanded tests as well as to enhance understanding the fracture of rock-like material.     

Fracture prediction of thin plates under localized impulsive loading. Part II: discing and petalling

The onset of fracture and subsequent propagation of radial cracks of thin clamped circular plates under localized impulsive loading were predicted analytically and numerically for discing and petalling stages with increasing intensity of applied impulse and various radii of loaded area. The equivalent plastic strain times the average stress triaxiality was introduced as a ductile fracture criterion in the numerical simulation. The strain hardening law and critical damage/fracture function was calibrated from tensile test on round specimen and a parallel numerical simulation. Based on the critical damage value, and calculated distributions and histories of stress and strain, the initiation site and extent of fracture were predicted for a range of loading radii and intensity of applied impulse. It was clearly demonstrated that the crack length and final deformed shapes of plates are strongly influenced by the spatial distribution and intensity of impulsive loading. A comparative study on the propagation of radial cracks was also presented. Finally, the numerically obtained crack length was shown to agree well with the closed form solution derived earlier by one of the present authors.     

循环荷载作用下超高性能混凝土的轴拉力学性能及本构关系模型

对具有不同拉伸应变特性(应变强化和应变软化)的超高性能混凝土(Ultra high performance concrete, UHPC)进行了单调和循环荷载作用下的直接拉伸试验。试验结果表明:应变强化UHPC基体开裂后进入多点微裂纹分布的应变强化段,达到极限抗拉强度后进入单缝开裂的应变软化段;应变软化UHPC基体开裂后直接进入单缝开裂的应变软化段;循环荷载下两种类型UHPC的轴拉应力-应变曲线包络线与单调荷载下的应力-应变曲线基本一致;基于刚度退化过程建立了两种类型UHPC的轴拉损伤演化方程,根据实测应力-应变曲线和试件的裂缝分布形态建立了两种类型UHPC的轴拉本构关系模型,与试验结果基本吻合;采用能量法研究了应变强化UHPC两阶段轴拉本构关系在数值计算时的等效方法。最后,通过无筋应变强化UHPC抗弯试验梁的数值模拟对本文建立的应变强化UHPC轴拉本构关系模型和损伤演化方程及相关假定进行了验证,结果表明本文建立的应变强化UHPC轴拉本构模型能较好地预测UHPC弯拉构件的极限承载力,轴拉损伤变量能在宏观层面上较好地反应试件的裂缝分布状态。      

Threshold Identification for Micro‐Tomographic Damage Characterisation in a Short‐Fibre‐Reinforced Polymer

The micro‐tomographic technique represents an important tool for the analysis of the internal structure in short‐fibre‐reinforced polymers samples. For the investigation of damage mechanisms, detection of the micro‐voids within the matrix can be facilitated by applying a tensile load in‐situ during the scan. The investigations here described started from two micro‐CT acquisitions, at different strain levels, of the same PA6.6GF10 sample. An original procedure for micro‐voids identification is proposed, based on the statistical elaboration of the matrix grey‐tone range. In order to validate the suggested procedure beyond visual inspection, an independent method based on an optimisation approach, which puts to use the two available micro‐tomographic sets, was developed and applied. The effect of the tensile load, which can induce a progression of the damage within the specimen, was investigated, and the relations among strain, fibre distribution and micro‐voids volumetric fraction were studied. Our findings point out that the mechanisms of damage progression, even under static loading as in this case, appear to be more complex than those related to the fibre‐density‐induced stress concentrations alone and require further investigation.     

MIXED MODE SMALL CRACK GROWTH

Abstract— The fatigue crack growth behavior of small part-through cracks in 1045 steel and Inconel 718 subjected to biaxial loading has been investigated. Experiments were performed on thin-wall tubular specimens loaded in tension, torsion and combined tension torsion. Crack sizes analyzed ranged from 20 μm to 1 mm and growth rates ranged from 10^-7 to 10^-4 mm/cycle for 1045 steel and from 10^-5 to 10^-2 mm/cycle for Inconel. Nucleation and the early growth of cracks occurs on planes of maximum shear strain amplitude for both of these materials even in tensile loading. An equivalent strain based intensity factor was employed to correlate the crack growth rate under mixed mode loading conditions In loading conditions other than torsion, a transition from mode II to mode I was observed for 1045 steel. Principal strains were used to analyze mode I cracks. Cracks in Inconel 718 grow in mode II for the majority of the fatigue life. The maximum shear strain amplitude and the tensile strain normal to the maximum shear strain amplitude plane were used to calculate the strain based intensity factor for mixed mode loading.     

拉—拉疲劳下15MnMoVN多裂纹扩展研究

为分析单裂纹或多裂纹在裂纹面承受疲劳拉伸载荷作用下尖端应力强度因子变化规律和裂纹形貌变化以及疲劳寿命情况,以含不同初始长深比的半椭圆单裂纹或双裂纹的薄片试样为研究对象,对试样在应力比R=0.1的疲劳拉伸载荷下单裂纹或双裂纹情况进行了仿真分析。建立含裂纹试样的有限元模型,仿真分析了裂纹在扩展过程中尖端应力强度因子的分布情况,并将单裂纹扩展结果与双裂纹相互作用影响下的结果进行了对比研究;进行含裂纹试样的疲劳实验,分析了含单裂纹或双裂纹的试样的断裂面的形成原因,并验证仿真结果正确性。结果表明,裂纹面之间的相互作用会逐渐影响裂纹的扩展方向、扩展速率以及在扩展过程中尖端应力强度因子的变化趋势;而且初始形貌为半椭圆形的双裂纹在相互作用影响下会逐渐过渡到半圆形。