等规度分布对双向拉伸聚丙烯非等温结晶动力学的影响

利用差示扫描量热仪研究了等规度分布对两种双向拉伸聚丙烯(BOPP)薄膜专用料的非等温结晶动力学的影响。非等温结晶动力学结果表明:随降温速率的增大,两种BOPP膜的结晶起始温度T0、结晶终了温度T∞、结晶峰值温度Tp、结晶焓均降低;结晶速率常数Zc增大,半结晶时间t1/2逐渐缩短,结晶过程中的生长维数n在1~3之间;F(T)逐渐增大,a值逐渐减小。样品的等规度分布越均一,则其结晶速率越慢,半结晶时间t1/2越长,结晶速率常数Zc越小。     

梯级送风对冷藏车厢内温度场的影响分析

合理的厢内温度场是保证冷藏车运输货物品质、节能降耗的关键因素之一。为提高厢内温度场的均匀性,本文提出了单温区冷藏车的梯级送风模式。无梯级送风时,冷风在车厢内形成整体环流,流动方向较为集中,不利于整体降温;有梯级送风时,车厢顶部增加了风机,冷风速度得以提高,且流动方向更加分散,有利于提高整体降温速度和温度场均匀性。建立了冷藏车厢的仿真模型,利用CFD研究梯级送风对空仓时冷藏车厢内温度场的影响,并进行了实验验证。以射流区平均温度、车厢内整体平均温度、温度场不均匀系数和温度极差作为评价指标,对实验中采集到的温度数据进行对比分析。结果表明：梯级送风模式能够有效降低冷藏车厢内的射流区平均温度、整体平均温度、温度场不均匀系数,减小温度极差,提高降温速度;在射流区,梯级送风的影响最为显著,该处的降温幅度和降温速度都有明显优化;在车厢尾部近地面的拐角处,梯级送风的降温效果虽不明显,但降温速度明显加快。     

侧墙上置风口置换通风规律的实验研究

针对侧墙上置风口置换通风方式,测试了房间非等温送风射流发展的速度场和室内空间的温度场,利用送风射流无因次速度变化曲线,分析了组合射流发展规律及其对通风效率的影响,基于送风速度与热源强度双因素,阐明了耦合作用对通风效率的影响,并指出了风口结构对通风效率影响.     

自由磨料射流轴心磨料速度模型及分析

为了研究自由磨料射流轴心磨料速度,以自由磨料射流轴心磨料为研究对象,利用自由磨料射流轴心流体速度方程及磨料运动方程,建立了自由磨料射流轴心磨料速度模型,并基于等分法和迭代算法的数值求解方法,求解了该速度模型,得出了自由磨料射流轴心磨料速度变化规律,最后利用PIV实验对该速度模型进行了验证。结果表明:(1)自由磨料射流轴心磨料速度随着磨料运动距离的增加先增大后减小;在初始段末端磨料速度未达到速度最大值,磨料速度最大值出现在基本段内。(2)自由磨料射流轴心磨料速度PIV实测值与理论值的变化趋势基本一致;实测值与理论值的平均百分比误差和标准偏差分别小于3%和2 m/s,吻合较好,验证了模型的正确性和准确性。     

CFRP拉挤过程非稳态温度场数值模拟与FBG实时检测

碳纤维增强聚合物基复合材料的拉挤成型过程是动态的,其固化度与温度变化为强耦合关系。温度场是工艺过程控制关键之一。根据固化动力学和传热学理论,建立了非稳态温度场与固化动力学数学模型。通过差示扫描量热仪（DSC）分析计算出模型中固化动力学参数。采用有限元与有限差分相结合的方法,依据ANSYS求解耦合场的间接耦合法,编制了计算程序,对拉挤工艺不同工况CFRP内部非稳态温度场进行数值模拟。采用专门设计制作的铝毛细管封装的布拉格光栅光纤(FBG),排除了非温度应变的干扰。通过试验确定了FBG温度传感特性表征及FBG温度灵敏度系数值,保障了CFRP内部温度场实时动态检测的准确度。模拟与实验结果基本吻合,为取代传统试凑性实验,优化CFRP拉挤工艺提供了科学快捷的理论依据。      

粉末药型罩聚能射流形成过程中温度分布及影响分析

根据石油射孔弹的实际结构和几何尺寸,运用ANSYS/LS-DYNA-2D非线性动力学有限元分析软件,采用瞬态非线性的热耦合计算方式,对孔隙率为11.53%的铜药型罩射流形成过程中典型瞬态的温度场进行描述和分析;对多孔药型罩聚能射流的最高温度-时间曲线进行研究,并对射流自身是否产生熔化进行判断;对比了多孔药型罩与密实药型罩聚能射流轴线和外表面温度。结果表明:聚能射流轴线温度高,由轴线向外表面逐渐降低,最高温度先增大,11μs增到最大1 743K后减小,最后几乎不变,约为1 378K,多孔药型罩比密实药型罩聚能射流的温度高,延伸性能和稳定性能更好。     

粉末药型罩聚能射流形成过程中温度分布及影响分析

根据石油射孔弹的实际结构和几何尺寸,运用ANSYS/LS-DYNA-2D非线性动力学有限元分析软件,采用瞬态非线性的热耦合计算方式,对孔隙率为11.53%的铜药型罩射流形成过程中典型瞬态的温度场进行描述和分析;对多孔药型罩聚能射流的最高温度-时间曲线进行研究,并对射流自身是否产生熔化进行判断;对比了多孔药型罩与密实药型罩聚能射流轴线和外表面温度。结果表明:聚能射流轴线温度高,由轴线向外表面逐渐降低,最高温度先增大,11μs增到最大1 743K后减小,最后几乎不变,约为1 378K,多孔药型罩比密实药型罩聚能射流的温度高,延伸性能和稳定性能更好。     

雾化气体淬火过程耦合流场数值模拟及实验研究

运用计算流体动力学(CFD)的方法在FLUENT平台上建立雾化气体淬火的三维非稳态模型,对介质不同速度工况下淬火过程中试件温度场、流体速度场、流体温度场和流体压力场进行了流固热耦合数值模拟,并将模拟结果与边界条件实验结果进行了对比分析。结果表明,同等工况下,介质进口速度越大,流体的速度也越大;同截面上200m/s速度工况下试件上下表面两区域的压力差值比100m/s速度工况下大;试件放在淬火区淬火80s后,200m/s速度工况下试件的最高温度为299.5℃,100m/s速度工况下试件的最高温度为336℃,由此得出淬火介质进口速度越大,淬火试件的温度下降越快,试件冷却速度越快,冷却效果越好。     

船用低合金高强钢止裂温度相关性研究

为研究不同温度场条件下所测止裂温度的相关性,针对4种批号船用低合金高强钢,分别开展等温型双重拉伸试验和梯度温度型(以下简称"梯温型")双重拉伸试验,测得了等温型止裂温度和梯温型止裂温度.结果表明,在同一主拉伸应力水平下,梯温型止裂温度值均高于等温型止裂温度值,两者差值与主拉伸应力近似呈线性增长关系、与板厚近似呈二次函数...     

不同构造冷藏车厢体的冷却性能模拟与比较

本文针对4种结构不同的冷藏车厢体,在相同的运输时间下采用同样货物堆码方式,以苹果为实验材料,利用CFD模拟4种厢体在特定风速、特定制冷温度下其内部温度分布情况,并对厢体冷却性能(温度分布、冷却时间、冷却均匀性)进行对比与分析。经过模拟180 min的冷藏运输结果表明:同时安装侧通风槽及地导轨与单独安装侧通风槽的厢体内部货物温度变异系数分别为0.001 3、0.001 5,冷藏运输后温度在3~4.5℃范围内的货物比重分别为62.06%、59.26%,货物平均温度分别为4.3℃、4.6℃;无导轨型厢体与单独加装地导轨厢体货物的温度变异系数分别为0.002 4、0.002 1,冷藏运输后温度在3~4.5℃范围内的货物比重分别为52.54%、53.44%,货物平均温度分别为5.0℃、4.9℃。结果表明:温度的最大均方根误差分别为0.221℃、0.198℃,最大平均相对误差为18.35%、16.91%,风速模拟值与实测值的最大偏差为0.3 m/s,得出实验值与模拟值有较好的一致性。     

Nonlinear dissipative spring mass model for a percussive drill rod joint of the coupling sleeve type

A nonlinear dissipative spring mass (NDSM) model for a percussive drill rod joint of the coupling sleeve (CS) type is established. Such a joint consists of a cylindrical coupling sleeve with internal thread which connects two drill rods with external threads at their ends. The model disregards wave motion in the coupling sleeve but accounts for axial mobility of the sleeve relative to the rods. This mobility is due to local deformation and slip of the threads. The model is characterized by the mass of the sleeve and by three parameters which represent the coupling between the sleeve and the drill rods through the threads. A static and a dynamic test have been developed for determining the coupling parameters. The model is validated by simulating previous impact tests with a commercial CS joint. Good agreement is obtained between theoretical and experimental results for waves and energies by using values for the two stiffness parameters from the static tests and for the friction parameter from the dynamic tests. Then, the discrepancies for transmitted and dissipated energy are only of the magnitude of the estimated error in the impact tests.     

MT300/KH420碳纤维/聚酰亚胺树脂复合材料层合圆柱壳高温承载性能

基于Donnell-Mushtali近似理论及热弹性理论,考虑结构热变形和材料高温性能衰减等温度影响因素,对MT300/KH420碳纤维/聚酰亚胺树脂复合材料圆柱壳在常温、420℃及周向210~420℃不均匀温度场等热载工况下的承载性能进行了理论分析。并引入一阶屈曲模态缺陷作为几何初始扰动,利用ABAQUS,采用非线性显式动力学方法完成对MT300/KH420复合材料圆柱壳在以上热载工况下的轴压稳定性有限元仿真计算,计算结果与理论分析较为一致。设计并开展MT300/KH420复合材料圆柱壳力-热载荷联合轴压试验,获得圆柱壳在以上热载工况下的破坏载荷和破坏模式。研究表明:高温工况下,力学性能衰减和温场不均匀引起的结构热变形是影响MT300/KH420复合材料圆柱壳轴向失稳载荷的主要因素。      

高温烧蚀条件下 C/C材料热力耦合场模拟

热防护材料在高温、高焓、高压环境中因物理、化学和力学因素造成质量损失引起材料烧蚀,使其热力学和热物理性质发生不可逆变化, 表现出复杂的非线性特征。通过对碳基复合材料热化学烧蚀机理分析, 由质量守恒、能量守恒及系统化学反应的热化学平衡原理, 建立相应的热化学和热力学烧蚀模型。基于材料线烧蚀引起边界移动建立热传导方程; 对温度场以及热应力场求解时充分考虑材料变物性特征。通过数值模拟表征材料在高温烧蚀条件下的动态热力学行为, 与实验结果吻合较好, 实现了材料在高温、高过载等复杂因素耦合作用下的实时仿真。      

动载下胶结充填体的力学特性试验研究

胶结充填体的稳定性对于矿山安全生产至关重要。为了研究动载作用下充填体的动力学特性,利用霍普金森压杆(SHPB)对充填体进行单轴冲击试验,研究充填体应力应变曲线、动态抗压强度、动态强度增长因子与平均应变率之间的关系。结果表明,当平均应变率低于60 s^(-1)时,应力应变曲线峰后阶段为"应变回弹"类型;超过80 s(-1)时,应力应变曲线峰后阶段为"应变回弹"类型;超过80 s^(-1)时,为"峰后塑性"类型;介于二者之间时,为"应力跌落"类型;随着平均应变率的增大,试样动态抗压强度先迅速增大,后趋于稳定,对应的平均应变率临界值为80 s(-1)时,为"峰后塑性"类型;介于二者之间时,为"应力跌落"类型;随着平均应变率的增大,试样动态抗压强度先迅速增大,后趋于稳定,对应的平均应变率临界值为80 s^(-1)。利用Gompertz模型能较好的描述充填体动态抗压强度与平均应变率之间的关系;动态强度增长因子与平均应变率正相关,当平均应变率处于40～130 s(-1)。利用Gompertz模型能较好的描述充填体动态抗压强度与平均应变率之间的关系;动态强度增长因子与平均应变率正相关,当平均应变率处于40～130 s^(-1),动态强度增长因子范围在1.5～3之间。     

钻爆法施工中单孔爆破的精细化数值模拟

针对钻爆法施工中常见的炮孔装药结构和围岩条件,建立相应的数值模型,对单孔爆破进行流固耦合的精细化数值模拟。以轴向不耦合系数K_L=1.64的炮孔为例,设其粉碎区和破裂区的形成时间约为100μs和500μs,半径分别为炮孔半径的3.9倍和35倍。当炮孔有效半径(近似粉碎区与破裂区交界处)上径向压力时程的峰值达到296 MPa时,沿着径向呈指数型衰减,其衰减系数α约为-0.87。进一步地,对其余4种不同轴向不耦合系数的炮孔,也展开类似的精细化数值模拟。认为有效半径R_(eq)上的径向压力峰值p_(eq)随不耦合系数K_L的增大呈指数型衰减,并提出了相应的半理论半经验公式。研究结果为进一步确定等效爆破荷载提供了重要依据。     

Experimental study on impact behaviour of concrete-filled steel tubes at elevated temperatures up to 800 °C

The dynamic behaviour of normal strength concrete-filled steel tubes (CFT) at elevated temperatures up to 800 °C under axial impact loading was experimentally studied by using a newly developed spilt Hopkinson pressure bar (SHPB) together with an electrical furnace. The effects of high temperature, impact velocity, steel ratio and slenderness ratio on the impact behaviour of CFT at elevated temperatures were experimentally studied. The stress and strain time history curves of the tested specimens were recorded to analyze the impact behaviour of CFT at elevated temperatures. The failure modes and the effects of the experimental parameters on the impact resistance of CFT are discussed. The test results showed that normal strength concrete-filled steel tube at elevated temperatures had a more excellent impact resistance in the paper than that described in Huo et al. (2009). A simplified calculation method was updated by introducing the reasonable dynamic increase factor model of hot concrete to reasonably assess the impact resistance of CFT at elevated temperatures.     

Thermomechanical response of HSLA-65 steel plates: experiments and modeling

To understand and model the thermomechanical response of high-strength low-alloy steel (HSLA-65), uniaxial compression tests are performed on cylindrical samples, using an Instron servohydraulic testing machine and UCSD’s enhanced Hopkinson technique. True strains exceeding 60% are achieved in these tests, over the range of strain rates from 10⁻³/s to about 8500/s, and at initial temperatures from 77 to 1000 K. The microstructure of the undeformed and deformed samples is examined through optical microscopy.The experimental results show: (1) HSLA-65 steel displays good ductility and plasticity (strain > 60%) even at low temperatures (even at 77 K) and high strain rates; (2) at relatively high temperatures and low strain rates (especially below about 0.1/s), its strength is temperature-insensitive, indicating that the material has good high-temperature weldability; (3) slight dynamic strain aging (DSA) occurs at temperatures over 400 K and in the range of strain rates from 0.001/s to 3000/s, the maximum values of the stress shifting to higher temperatures with increasing strain rates; and (4) the microstructure of the material is not affected much by the changes in the strain rate and temperature.Finally, based on the mechanism of dislocation motion, and using our experimental data, the parameters of a physically-based model developed earlier for AL-6XN stainless steel [J. Mech. Phys. Solids 49 (2001) 1823] are estimated and the model predictions are compared with various experimental results, excluding the dynamic strain aging effects. Good agreement between the theoretical predictions and experimental results is obtained. In order to further verify the model independently of the experiments used for the evaluation of the model parameters, additional compression tests at a strain rate of 8500/s and various initial temperatures are performed, and the results are compared with the model predictions. Good correlation is observed. As an alternative to this model, the experimental data are also used to estimate the parameters in the Johnson–Cook model [Proceedings of the Seventh International Symposium on Ballistics, The Hague, The Netherlands, p. 541] and the resulting model predictions are compared with the experimental data, again excluding the dynamic strain-aging effects. These and related results suggest that the physically-based model has a better prediction capability over a broader strain rate and temperature range.     

Temperature dependence of electron-to-lattice energy transfer in single-wall carbon nanotube bundles

The electron-phonon coupling strength in single-wall carbon nanotube (SWNT) bundles has been studied directly in the time domain by femtosecond time-resolved photoelectron spectroscopy. We have measured the dependence of H(Te, Tl), the rate of energy transfer between the electronic system and the lattice as a function of electron and lattice temperatures Te and Tl. The experiments are consistent with a T5 dependence of H on the electron and lattice temperatures, respectively. The results can be related to the e-ph mass enhancement parameter lambda. The experimentally obtained value of for lambda/[symbol: see text] D2, where [symbol: see text] D is the Debye temperature, suggests that e-ph scattering times at the Fermi level of SWNT bundles can be exceptionally long, exceeding 1.5 ps at room temperature.     

不同强度混凝土高温下动态劈拉性能研究

采用大直径分离式霍普金森压杆(SHPB)装置和加温装置,在不同温度(20 ℃、200 ℃和400 ℃)下对3种不同强度(C20、C45和C70)混凝土材料开展不同应力率的动态劈裂拉伸实验,得到了温度和应力率耦合作用下混凝土材料的动态劈裂强度及相应的破坏形态。实验结果表明,混凝土材料的动态劈裂强度随应力率的增加而增加,且应力率相近时,其动态劈裂强度随温度的增加而明显降低。在此基础上给出了描述混凝土材料在不同温度下的动态劈裂强度与应力率关系的表达式,并确定了相关材料参数。通过对不同应力率和温度耦合作用下混凝土材料的动态劈裂强度进行横向对比,发现混凝土材料动态劈裂强度的温度敏感性随应力率的增加逐渐减小,并且随着混凝土材料强度的增加其温度敏感性也逐渐变小,但是其动态劈裂强度的应力率敏感性却随着温度的升高逐渐增大。     

Determination of inelastic heat fraction of OFHC copper through dynamic compression

An approach to determine the inelastic heat fraction (IHF) value of metal by high-speed compression is established by combining dynamic deformation, infrared (IR) photography and finite element simulation. OFHC copper specimens are dynamically compressed and infrared thermographs captured at a rate of 1000 images/s. FEM simulation of the deformation is undertaken and the initial IHF value input adjusted until the computed average surface temperature matches the experimental data. It is found that for the IHF value identified, the predicted surface temperature distribution also exhibits good correlation with experimental results. For final strains in the range of 44–60%, a consistent IHF value of 0.68 is obtained. Using this value, the surface temperature of a sample deformed to a different final strain and at a different strain rate is predicted by FEM simulation and the numerical results show good agreement with test data in terms of average surface temperature and surface temperature distribution. The temperature field for the entire specimen is also predicted. Results indicate that high-speed compression at a strain rate of 1000/s to a final engineering strain of 70% may result in initiation of dynamic recovery in OFHC copper.