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为了研究爆炸荷载下青砂岩I型裂纹动态断裂韧度的测试方法,利用内部中心单裂纹圆盘(internal center single crack disc,ICSCD)试样进行了爆炸试验研究。试样由外径为400 mm、内部加载孔径为40 mm、预制裂纹长为60 mm的青砂岩制成。利用同步触发器实现圆盘中心起爆,并同步触发超动态应变仪,通过径向应变片获取爆炸应变曲线、裂纹尖端的环向应变片获取裂纹起裂时刻。以实测爆炸应变曲线为参量,应用Laplace变换推导出试样加载孔壁应力时程曲线表达式,并用数值反演法得出其数值解。利用ANSYS有限元软件,建立数值计算模型,通过相互作用积分法得出了在爆炸荷载作用下砂岩的I型动态应力强度因子曲线。研究结果表明:(1)ICSCD试件能够很好地用来测试岩石的动态起裂韧度;(2)炮孔周边的应力可以通过拉普拉斯变换的数值反演方法得到;(3)通过试验-数值法能稳定计算出ICSCD砂岩构型的动态起裂韧度,其最大误差仅为7%。
相似文献3.
岩石动态断裂韧度的尺寸效应 总被引:1,自引:0,他引:1
采用两种圆孔裂缝平台巴西圆盘试件(一种为直径分别为42、80、122、155 mm的几何相似试件,另一种为直径80 mm、仅裂缝长度不同的单一尺寸试件)对岩石动态断裂韧度的尺寸效应进行了研究。给出了在霍普金森压杆系统上对试件进行径向撞击产生的应变波形和断裂模式。实验结果表明,对于几何相似试件,动态断裂韧度的测试值随着尺寸的增大而增大,而对于单一尺寸试件,其测试值随着中心裂缝长度的增加呈现先增大后减小的趋势。裂缝前端的断裂过程区长度和孕育时间是岩石动态断裂韧度测试值表现为尺寸效应的主要原因,为了减小尺寸效应,建立了考虑这两个参数在空间-时间域对动态应力强度因子的分布进行积分后再平均来确定岩石动态断裂韧度的方法。 相似文献
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介绍了设计的新型圆台式压头及配套的衬片加载部件,推导了采用新的加载部件进行冲击断裂实验时的断裂韧度计算公式。采用SHPB实验装置,用新加载部件对带有V形切口的无烟煤短棒试件的裂纹尖端施加拉伸载荷,测定了无烟煤的动态断裂韧度。结合准静态实验数据得到了无烟煤断裂韧度随加载率lg(dF/dt)的总体变化规律:当lg(dF/dt)6时,无烟煤的断裂韧度缓慢上升,但当lg(dF/dt)6以后,无烟煤的断裂韧度随加载率的增加快速增大。实验表明:圆台式加载比刀刃式加载更具优越性和适应性,是测试岩石类材料短棒试件动态断裂韧度较好的方法。 相似文献
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高应变率下断裂韧性实验的数值模拟 总被引:1,自引:0,他引:1
采用有限元软件ANSYS/LS-DYNA程序对静态和冲击荷载作用下的含裂纹半圆弯曲(SCB)实验进行了数值模拟。根据静态实验的模拟结果,提出了适合复合型加载的Ⅰ型应力强度因子拟合公式,采用该公式计算应力强度因子的最大误差不超过10%。动态实验的模拟结果表明:对于纯Ⅰ型加载的SCB实验,动态应力强度因子随着试样半径、支座间距以及相对裂纹长度的变化呈现规律性变化;当试样半径小于60mm、相对支座间距为1.2、相对裂纹长度在0.1~0.4范围内时,惯性效应的影响较小,采用静态拟合公式计算裂尖的动态应力强度因子的误差约10%;对于复合型加载的SCB实验,当相对裂纹长度为0.2~0.4、裂纹倾角在10°~40°范围内时,采用静态拟合公式计算裂尖的动态应力强度因子的误差小于10%。 相似文献
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增韧环氧树脂的动态裂纹扩展研究 总被引:1,自引:0,他引:1
本文主要进行了环氧及增韧环氧树脂的断裂韧性及裂纹快速扩展的试验研究。试验过程中采用了GLC-1型高速裂纹扩展测试仪来测试裂纹的扩展速度,得到在裂纹扩展过程中裂纹扩展速度曲线。本文结合不同的计算公式及有限元分析方法,讨论了各个确定断裂韧性公式的准确程度,发现传统的静态断裂韧性的分析方法所得到的结果偏大,有一定的危险性,建议使用试验与数值计算相结合的方法;同时还发现增韧不仅可以提高材料的静态和动态断裂性能,而且在裂纹扩展过程中可以起到减缓裂纹扩展的作用 相似文献
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James F. Doyle 《Experimental Mechanics》1984,24(1):10-16
An experimental method is investigated whereby the strain response from an impacted beam is sufficient to determine the contacting force. Once the force is known, it is shown how the contact law can be determined. Experimental results for an impacted aluminum beam are demonstrated. 相似文献
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Brittle fracture: Variation of fracture toughness with constraint and crack curving under mode I conditions 总被引:1,自引:0,他引:1
The effect of constraint on brittle fracture of solids under predominantly elastic deformation and mode I loading conditions
is studied. Using different cracked specimen geometry, the variation of constraint is achieved in this work. Fracture tests
of polymethyl methacrylate were performed using single edge notch, compact tension and double cantilever beam specimens to
cover a bread range of constraint. The test data demonstrate that the apparent fracture toughness of the material varies with
the specimen geometry or the constraint level. Theory is developed using the critical stress (strain) as the fracture criterion
to show that this variation can be interpreted using the critical stress intensity factorK
Cand a second parameterT orA
3,whereT andA
3are the amplitudes of the second and the third term in the Williams series solution, respectively. The implication of this
constraint effect to the ASTM fracture toughness value, crack tip opening displacement fracture criterion and energy release
rateG
Cis discussed. Using the same critical stress (strain) as the fracture criterion, the theory further predicts crack curving
or instability under mode I loading conditions. Experimental data are presented and compared with the theory. 相似文献
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A novel method for measuring and characterizing dynamic fracture-initiation toughness of elastic-plastic materials 总被引:5,自引:0,他引:5
The characterization and testing methods of the dynamic fracture initiation toughness of elastic-plastic materials under tensile
impact are studied. By using the self-designed bar-bar tensile impact apparatus, a novel test method for studying dynamic
fracture-initiation has been proposed based on the one-dimensional test principle. The curve of average loadv. s. displacement
is smooth until unstable crack propagation, and the kinetic energy which does not contribute to the crack growth can be removed
from total work done by external-force to the specimen. The fracture-initiation point is determined by compliance-changing
rate method. The results show that these methods are feasible and effective. Through the analysis of the conversion between
work and energy of a fracture specimen, the dynamicJ-integral is adopted as a characteristic parameter for elastic-plastic materials under impact loading. TheJ-integral is calculated from
and
curves by using the formula proposed, by Rice. TheJ-integral at fracture initiation is employed to describe the dynamic fracture-initiation toughness of elastic-plastic materials
and the experimental results indicate thatJ
ID can be regarded as a material constant. 相似文献
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Dynamic fracture toughness of high strength metals under impact loading: increase or decrease 总被引:1,自引:0,他引:1
An elusive phenomenon is observed in previous investigations on dynamic fracture that the dynamic fracture toughness(DFT) of high strength metals always increases with the loading rate on the order of TPa.m 1 /2.s 1.For the purpose of verification,variation of DFT with the loading rate for two high strength steels commonly used in the aviation industry,30CrMnSiA and 40Cr,is studied in this work.Results of the experiments are compared,which were conducted on the modified split Hopkinson pressure bar(SHPB) apparatus,with striker velocities ranging from 9.2 to 24.1 m/s and a constant value of 16.3 m/s for 30CrMnSiA and 40Cr,respectively.It is observed that for 30CrMnSiA,the crack tip loading rate increases with the increase of the striker velocity,while the fracture initiation time and the DFT simultaneously decrease.However,in the tests of 40Cr,there is also an increasing tendency of DFT,similar to other reports.Through an in-depth investigation on the relationship between the dynamic stress intensity factor(DSIF) and the loading rate,it is concluded that the generally increasing tendency in previous studies could be false,which is induced from a limited striker velocity domain and the errors existing in the experimental and numerical processes.To disclose the real dependency of DFT on the loading rate,experiments need to be performed in a comparatively large striker velocity range. 相似文献
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大体积混凝土等效裂纹断裂模型研究 总被引:7,自引:0,他引:7
根据大比尺混凝土紧凑拉伸与楔入劈拉试验成果,将裂纹在稳定扩展中断裂有程区应力分布与相应的变形(张开度ω)联系起来,通过“归一化”处理,得到了大体积混凝土断裂过程区长度的解析表达式,建立了大体积混凝土Ⅰ型断裂破坏的等效裂纹断裂模型。 相似文献
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裂纹面摩擦接触引起的断裂韧性增长的研究 总被引:4,自引:2,他引:2
采用弹黏塑性的材料本构关系, 建立了压、剪混合型裂纹常速准静
态扩展的力学模型, 求得了裂纹面摩擦接触条件下裂纹尖端场的数值解, 并基于数
值结果讨论了扩展裂纹的摩擦效应. 计算和分析表明, 裂纹面的摩擦效应主要表现
在两个方面. 第一方面是摩擦会导致裂纹尖端区材料的断裂韧性增高,
并且裂纹面间的摩擦作用越强, 增韧效果越显著. 摩擦增韧的机制可以解释为裂纹
面间的摩擦作用导致裂纹尖端塑性区尺寸变大, 使裂纹尖端场的塑性变形能增加,
从而使得裂纹尖端区材料增韧. 摩擦生热并不是导致材料断裂韧性增长的根本机制.
第二方面是摩擦会导致``断裂延缓'.
利用裂纹面的摩擦来提高构件的承载能力和延长构件的服役寿命具有较大的工程实用价值. 相似文献
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The equation of static and dynamic caustics, and the formulae determining the position of crack tip and stress intensity factor
are given. It is proven that for the case of low speed of crack propagation the static formula is applicable in calculation.
A simple method to measure the static stress-optical constants is proposed. An Optical system which is suitable for the experiments
of dynamic caustics was set-up and used to study the fracture in beam and rings with initial crack under impact loading. A
series of dynamic caustics' photographs and curves showing the variations of corresponding crack lengths and dynamic stress
intensity factors with time, are presented. 相似文献
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The heat generated from dissipative mechanisms during shearing and opening dominated dynamic fracture of polymethyl methacrylate
and polycarbonate was measured with a remote sensing technique that utilizes the detection of infrared radiation. Significant
heating was detected for both materials and both modes of fracture. In the shear dominated experiments, the temperature increase
at the crack tip in polymethyl methacrylate was 85 K, the approximate increase necessary to reach the glass transition temperature.
An adiabatic shear band followed by a dynamically propagating crack were observed during the shear dominated experiments using
polycarbonate. The recorded shear band temperature increase was 45 K. This was followed by an additional 100 K temperature
increase from the ensuing crack, raising the temperature above glass transition. The maximum temperature increase recorded
for the opening mode experiments was 55 K for polymethyl methacrylate and 105 K for polycarbonate. The results of this study
show that temperature effects are significant during the dynamic fracture of polymers. The effects are especially important
in the shear dominated case where local temperatures approach or exceed the polymer glass transition temperature. 相似文献
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The Small-Scale Steady State (S4) test has been recently developed in order to assess the fracture behaviour of polyethylene
(PE) gas distribution pipe material during rapid axial crack propagation. Based on an investigation of the S4 test, a simulation
model of S4 test has been developed. This paper describes the use of the results obtained from the S4 test and program modified
from PFRAC (Pipeline Fracture Analysis Code) to evaluate the fracture toughness of the material,G, which could not be directly obtained from the test, and to predict critical pressure,p
c
, for rapid crack propagation (RCP) in a full scale PE pipe. The algorithms for contact conditions are developed to consider
the opening pipe wall impact against a series containment rings and the capabilities of PFRAC are also extended. WhenG
d
is evaluated, investigations are made on the effect of temperature, wall thickness and crack velocity. In addition, procedures
to evaluate the critical pressure for the S4 test pipe are also discussed. 相似文献
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Zhenjun Yang 《Acta Mechanica Sinica》2006,22(3):243-256
The scaled boundary finite element method (SBFEM) is a recently developed numerical method combining advantages of both finite element methods (FEM) and boundary element methods (BEM) and with its own special features as well. One of the most prominent advantages is its capability of calculating stress intensity factors (SIFs) directly from the stress solutions whose singularities at crack tips are analytically represented. This advantage is taken in this study to model static and dynamic fracture problems. For static problems, a remeshing algorithm as simple as used in the BEM is developed while retaining the generality and flexibility of the FEM. Fully-automatic modelling of the mixed-mode crack propagation is then realised by combining the remeshing algorithm with a propagation criterion. For dynamic fracture problems, a newly developed series-increasing solution to the SBFEM governing equations in the frequency domain is applied to calculate dynamic SIFs. Three plane problems are modelled.
The numerical results show that the SBFEM can accurately predict static and dynamic SIFs, cracking paths and load-displacement curves, using only a fraction of degrees of freedom generally needed by the traditional finite element methods.The project supported by the National Natural Science Foundation of China (50579081) and the Australian Research Council (DP0452681)The English text was polished by Keren Wang. 相似文献