被动围压下浇注PBX炸药的动态力学性能研究

为获取一种浇注PBX炸药在被动围压加载下的动态力学性能,采用基于分离式霍普金森杆系统的被动围压试验装置开展了不同应变率(200、600 s^-1)下该浇注PBX炸药的力学性能测试,并通过改变围压管壁厚（4、10 mm）分析了围压应力对试样轴向应力的影响。结果表明:随着应变率和围压管壁厚的增加,被动围压下浇注PBX炸药的轴向应力（给定轴向应变）和围压应力（给定轴向应力）均呈增大趋势;且轴向应力随围压应力的增加呈指数增加。拟合得到被动围压下屈服点轴向应力与约束比之间的函数关系,与试验结果吻合良好。     

典型浇注PBX炸药的准静态压缩力学行为

采用定应变压缩试验研究了准静态压缩条件下浇注PBX炸药(浇注型高聚物黏结炸药)的力学行为,测试了典型浇注炸药PBX-1在损伤前、后的性能,获得了炸药的真应力-应变曲线。试验结果表明,浇注PBX炸药在准静态压缩条件下的力学行为分为接触压缩、弹性变形、损伤破坏和应变软化4个阶段。在压缩应变不超过损伤应变时,PBX-1炸药主要以弹性变形为主,屈服强度和屈服应变没有发生明显改变;在压缩应变超过损伤应变后,炸药中黏结剂断裂,颗粒脱黏,发生塑性变形。压缩应变增加至8%后,PBX-1炸药密度降低,残余应变增大;PBX-1炸药的屈服强度为0.6 MPa,屈服应变为10.6%,损伤应变为8%,炸药的损伤应变可以作为强度校核的依据。     

PBX炸药体膨胀特性研究

研制了适用于PBX炸药体膨胀的测试装置。采用此装置分别对热固型与热塑型PBX炸药的体膨胀力进行了测试,获得了两种炸药由常温升至75 ℃时的体膨胀力和体膨胀力随温度的变化曲线。试验结果表明,两种炸药的体膨胀力均是随着温度的升高而增加,在60～70 ℃范围内体膨胀力增加最大。炸药类型对炸药的体膨胀特性有较大的影响,热塑型PBX的体膨胀力远远大于热固型PBX的体膨胀力,是热固型炸药体膨胀力的8～9倍。对比不同质量的PBX-A炸药试验结果发现,随着炸药质量的增加,炸药体膨胀力随之增加;对体膨胀力-质量曲线进行线性拟合发现,体膨胀力随着质量的增加基本呈线性增长趋势。     

固化温度及固化剂种类对模拟PBX浇注炸药力学性能的影响

测试了端羟基聚丁二烯-异佛尔酮二异氰酸酯-三苯基铋（HTPB-IPDI-TPB）和端羟基聚丁二烯-六亚甲基二异氰酸酯三聚体-亚乙基二胺（HTPB-HDI-trimer-DABCO）两种黏结剂在不同固化温度下对模拟PBX浇注炸药的力学性能的影响。实验结果表明,随着固化温度的升高,HTPB-IPDI-TPB和HTPB-HDI-trimer-DABCO制备的模拟PBX浇注炸药药柱的力学性能增强。固化剂IPDI和HDI-trimer对药柱的机械性能有较大影响,与含IPDI炸药相比,含HDI-trimer的炸药药柱的剪切强度在35 ℃增大50.27%,45 ℃增大34.30%,55 ℃增大44.83%;抗拉强度在35 ℃降低82.66%,45 ℃降低78.73%,55 ℃降低82.22%;抗压强度在35 ℃增大54.85%,45 ℃增大45.25%,55 ℃增大53.38%。HDI-trimer形成三维网状结构降低了药柱的抗拉强度。     

分离式Hopkinson压杆数据处理系统的研制

根据分离式Hopkinson压杆试验的一维应力波加载理论,运用Visual C 6.0软件开发工具,编制了该类试验的后续数据处理系统。数据处理结果表明,该系统能有效地处理该加载系统上的动态拉伸、压缩,剪切及断裂试验。     

黏结剂相对分子质量对浇注PBX固化应力的影响?

采用自行研制的固化应力测试装置,测量了端羟基聚丁二烯(HTPB)基浇注高聚物黏结炸药(PBX)固化过程的应力变化,计算出固化应力数据,分析了黏结剂相对分子质量对热固性浇注PBX固化应力的影响,并对其在不同固化温度下的黏结强度进行了测试。结果表明:同一固化温度时,随着HTPB相对分子质量的逐渐增大,浇注PBX在固化阶段的最大热应力及收缩应力都逐渐减小。固化温度为100℃时,相对分子质量为1 500、2 800、4 000的HTPB基固化物因固化反应所产生的最大热应力分别为2.14、1.12、1.01 MPa,最大收缩应力分别为0.29、0.22、0.15 MPa。在固化降温阶段,HTPB相对分子质量越大,浇注PBX的收缩应力也越大。HTPB相对分子质量相同时,固化物的黏结强度随着固化温度的升高而降低;而固化温度一定时,HTPB相对分子质量对浇注PBX的黏结强度影响不大。     

小组分对热固性浇注 PBX 性能的影响?

通过对比热固性浇注PBX的渗油性、力学强度,探讨了配方中增塑剂、固化剂、键合剂等小组分对热固性浇注PBX炸药性能的影响。试验结果表明:增塑比增加,渗油率增加,试样力学强度降低;固化参数减小,力学强度降低,在固化参数小于0.8时渗油率明显增加;外加0.3%(质量分数)的键合剂可改善试样渗油率,并可明显增加试样力学强度,减少颗粒脱黏。     

PBX炸药共振声混合实验研究Ⅱ

通过共振声混合实验样机,对固含量为90%的PBX炸药进行了共振声混合的均匀性实验研究和机理分析,实验量级为300 g。实验结果表明,振动强度是影响PBX炸药混合的重要因素,振动强度过小或过大都不能实现被混物料内部的质量交换,并且在混合的不同阶段,由于物料性状不同,所需要的最佳振动强度也不同,90%固含量的PBX炸药所需的最佳振动强度在30～55左右,最佳混合方式是在一定范围内采用交变振动强度进行混合。     

PBX炸药声共振混合试验研究Ⅰ?

通过声共振混合试验样机对固体质量分数为86%的PBX炸药(高聚物黏结炸药)进行声共振混合的均匀性及工艺安全性试验研究,试验量级为150 g。试验结果表明,PBX炸药在声共振混合作用下进行内部的撕裂缠结,依次形成球状混合块和整场沸腾状混合浆,整个混合时间约为1 000 s。成分分析表明,声共振能实现固体质量分数为86%的PBX炸药均匀混合;静电和温度测量表明,整个混合过程中,静电电压几乎维持在0 k V左右,物料内部摩擦生热速度远远低于物料对外的热散失速度,混合过程中静电安全和热安全在可控范围内。     

浇注 PBX 固化温度场的数值模拟

为了使浇注塑料黏结炸药(PBX)具有均匀的固化温度场,采用COMSOL Multiphysics软件和Fourier数学模型,分别模拟研究了模具尺寸、烘箱与PBX间的温差、PBX固化速率等因素对PBX温度场分布的影响。结果表明:药浆温度低于烘箱温度时,浇注PBX内的温度场呈现由外向里递减的趋势。60 mm×240 mm、100 mm×240 mm、200 mm×240 mm和200 mm×1 000 mm,壁厚都为5 mm的模具,从25℃升至60℃的过程中,模具边缘和中心点的最大温差可分别达到3.22、6.66、10.49℃和13.08℃。200 mm×1 000 mm,壁厚为5 mm的模具分别从0、25、40、50℃升至60℃时,模具边缘和中心点的最大温差可分别达到17.56、13.08、7.02℃和3.36℃。药浆温度与烘箱温度相同时,模具边缘温度最小,中心温度最高,此时影响温度场梯度的主要因素为药浆固化速率的大小。当药浆和烘箱间存在温差,可通过减小模具尺寸、降低浇注PBX内的温度梯度,且浇注PBX的固化尽量采取药浆与烘箱温度一致的固化工艺,此时选择固化速率较小的药浆可实现PBX内的温度基本一致。     

SHPB冲击压缩实验中泡沫塑料应力均匀化过程的数值模拟

对SHPB实验中泡沫塑料的本构关系进行了分段线性化处理，基于一维弹性应力波理论用数值方法对变形过程进行了模拟。结果表明，实验初期试件处于严重的应力不均匀状态；并且由于试件与输入／输出杆的界面处存在波阻抗不匹配现象，实验中后期的应力均匀化程度也无法得到有效提高；若将子弹及输入／输出杆的材料更换为刚度较低的聚合物，可有效地减少波阻抗不匹配的程度，从而使实验中后期的应力均匀化水平得以大幅度提高，但实验所能够达到的最大应变值可能受到限制。     

Shear Band Evolution in Polymer Bonded Explosives Subjected to Punch Loading

The shear band development and potential hot‐spot initiation of polymer‐bonded explosive were investigated under low‐rate punch loading and combined punch and thermal loading. The digital image correlation method was used for deformation analysis. The obtained results showed that the initiation and development of shear bands at room temperature occur in three stages and demonstrated that the material suffers a prolonged shear stress concentration in a local area. Large shear was shown to lead to the formation of slip bands in the hard‐phase area, indicating that this region has the highest potential to initiate hot‐spots even under low‐rate punching. For high temperatures, the initiation and development of shear bands occur in two stages, with the resulting flow field being close to Hill's solution except for a small area directly underneath the punch. Large plastic flow rate was shown to be another important feature besides shear banding.     

Numerical simulation of the Split Hopkinson Pressure Bar test technique for concrete under compression

The Split Hopkinson Pressure Bar [SHPB] technique has been commonly used to investigate concrete compressive response under high strain rate. However, there appears to be a lack of agreement in the literature about a number of critical issues pertaining to this test method. In this paper, computational simulation models are employed to critique the technique and obtain a better understanding of it. Influential parameters are identified and attempts are made to shed light on some controversial issues surrounding the interpretation of high strain rate test data. The results show that significantly different strain rates can be obtained from the same SHPB test depending on the method used to estimate the strain rate value. Furthermore, comparing the results of simulations with pressure-independent and pressure-dependent constitutive material models show that strength increases associated with strain rate are strongly, but not totally, reliant upon the confinement introduced by lateral inertial effects and the frictional condition at the interface between the pressure bars and the specimen. Based on these observations, it is argued that the so-called ‘rate-enhanced’ models that explicitly account for strength increases as a function of strain rate should not be used in numerical simulations that already account for the effects of lateral confinement, since such models would tend to double-count the strain rate effect.     

Dynamic properties of pultruded natural fibre reinforced composites using Split Hopkinson Pressure Bar technique

The paper presents results on dynamic mechanical properties of jute, and kenaf fibre reinforced composites at various strain rates using compression Split Hopkinson Pressure Bar technique. The stress–strain curves for both pultruded natural fibre reinforced composites at strain rates of nearly 1400 s⁻¹ are illustrated and then compared with statically determines stress–strain curve (1.0 × 10⁻³ s⁻¹). Results show that the strain rate does affect the value of dynamic compressive properties of both pultruded natural fibre composites. Higher dynamic compression modulus and 2.5% flow stress were recorded for higher strain rates as compared to lower strain rate over the range of strain rates investigated. Under dynamic loading, jute fibre reinforced composites recorded the highest value of dynamic response in terms of compression modulus, 2.5% flow stress and compressive strength than that of kenaf fibre reinforced composites. In addition, kenaf fibre reinforced composites is more severely damaged as compared to jute fibre reinforced composites for all tested strain rate.     

高聚物复合材料动力学性能实验研究

橡胶类高聚物具有许多其它材料没有的高弹性、低弹性模量以及粘弹性等优越的动力学性能。随着防护工程建设的发展，这类材料的优越性能逐渐被工程界认识。本文用分离式Hopkinson压杆实验技术研究了不同掺料的四种橡胶复合材料在冲击荷载作用下的动力学性能，分析了其良好的吸能效果，实验中发现四种橡胶复合材料透射波幅值与入射波幅值的比值较低，表明其吸能率较高，尤以涤棉和尼龙两种材料吸能效果较好。     

精密铝铸件电磁泵负压充型测试技术

电磁泵负压充型工艺是在电磁充型低压铸造工艺的基础上发展而来的一种铸造技术, 其充型能力强, 补缩能力高. 相比较传统的反重力铸造技术, 该技术配合合适的浇注系统对铸件性能有明显的改善作用. 通过分析介绍其技术原理及特性, 该技术尤其适合复杂精密铝合金铸件的生产, 具有广阔的发展前景.     

模具定量精确成形技术在挤铸生产中的应用 研究

目的解决小型铝合金挤压铸件在浇铸过程中,存在的浇铸质量误差大、铸件组织的一致性较差、热节区出现组织缩松的问题,同时提高材料利用率。方法将模具定量精确成形技术引入到实际生产。结论模具定量精确成形技术的应用,能够有效解决小型铝合金挤压铸件在浇铸过程中因浇铸质量误差大的问题,铸件的总体质量误差能够控制在±0.02 kg范围以内,有效解决了因铸件质量误差大造成的铸件壁厚误差大,解决了铸件组织的一致性较差、热节区出现组织缩松的问题,提高了材料的利用率。     

Influences of Casting Pressure Conditions on the Quality and Properties of a Magnesium Cylinder Head Cover Die Casting

Casting pressure conditions have great influences on the casting defects, such as gas porosity, shrinkage porosity and gas holes. A Mg cylinder head cover die casting was used to experimentally study the influences of casting pressure, the loading time and the piston position of pressure intensification on the variation of pressure and the quality of casting. The results show that casting pressure, the loading time and the piston position of pressure intensification have great influences on the pressure variations in the mold, the quality and performance of casting. The external quality, the density and the tensile strength of casting were improved with the increase of casting pressure and the piston position of pressure intensification and the decrease of the loading time of pressure intensification.