共查询到20条相似文献,搜索用时 15 毫秒
1.
J. Jelwan 《Journal of Applied Mechanics and Technical Physics》2017,58(1):129-138
This paper re-examines the creep life methodology based on the continuum damage mechanics (CDM) of the Kachanov and Rabotnov theory. Uniaxial creep and multiaxial creep rupture formulations are presented taking into account the primary creep effect. The scalar damage parameter is computed up to time-to-rupture as a function of time and stress. The methodology implemented is based on the uniaxial time-to-rupture obtained experimentally. The times-to-rupture for bars with different notches are calculated. It is demonstrated that the use of the damage parameter is vital to indicate the critical damage location where failure occurs. Results are compared to those obtained experimentally. It is shown that the primary creep inclusion has a significant effect on the damage distribution zone. 相似文献
2.
A. M. Lokoshchenko V. V. Nazarov 《Journal of Applied Mechanics and Technical Physics》2007,48(4):542-546
The problem of the long-term strength of an extended thick-walled tube containing a corrosive medium in the internal cavity
is solved. The diffusion of this medium into the tube material is analyzed. The diffusion equation is solved approximately
by introducing the diffusion front, and the error of the solution is estimated. The dependence of the time of fracture of
the tube on the variable tensile stress and the concentration of the medium filling the cavity is obtained.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 4, pp. 88–93, July–August, 2007. 相似文献
3.
The first attempt of finding of optimal shape for bars in presence of body forces with respect to mixed creep rupture is made. For given volume of the bar, distribution of initial cross-section, ensuring the longest life-time to mixed rupture is sought. The finite strain theory and physical law in form of Norton's law generalized for true stresses and logarithmic strains are applied. Using the method of parametric optimization, the best of linear and quadratic functions describing the initial shape of the bar are found. The shape of initial strength is corrected in a way leading to longer life-time. Results of both approaches are compared. 相似文献
4.
为研究应变率对钢筋与混凝土界面粘结性能的影响,利用高速拉伸试验机进行了光圆钢筋的动态拔出实验。通过合理设计加载夹具和测试方法,得到不同应变率下光圆钢筋的“粘结-滑移”全程曲线。实验结果表明:随着应变率的增大,钢筋-混凝土界面的粘结强度显著提高,且界面失效形式由拔出失效为主转变为混凝土试件的破裂破坏为主;粘结强度的动态增强因子(fDIF)随应变率的增长斜率明显可以分为低应变率和高应变率两个区段。低应变率下,fDIF 增长较为缓慢;而高应变率下,fDIF快速增长;转变应变率约为33 s^-1。 相似文献
5.
大量锈蚀钢筋混凝土偏压构件的实验研究表明,随着纵向受力主筋锈蚀率的增大,偏心受压构件的承载力及其刚度均有不同程度的降低。并且由于钢筋锈蚀,钢筋混凝土偏心受压构件延性也随之降低,脆性性质明显,从而可能使得钢筋混凝土偏压构件的破坏形态发生变化。在对预制钢筋混凝土柱进行快速锈蚀实验85研究的基础上,对锈蚀偏心受压构件的结构性能退化机理和破坏特征进行了分析;在现行计算理论和实验85结果分析的基础上,通过拟合出的锈蚀钢筋与混凝土间的应变不协调系数,对未锈蚀构件的相对界限受压区高度进行修正,得到了锈蚀偏心受压构件相对界限受压区高度的修正公式;考虑锈蚀钢筋截面的削弱、钢筋屈服强度的降低以及钢筋和混凝土之间粘结性能退化的影响,提出锈蚀偏心受压构件正截面承载力计算方法,为今后混凝土结构耐久性评估和可靠性鉴定提供了科学依据。 相似文献
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动态拉伸试验中试样应变测试的有效性分析 总被引:3,自引:0,他引:3
为了评估将试样通过胶粘连接到加载杆的Hopkinson杆装置所获得试样应变的有效性,对四种强度刚度差异较大的纤维增强复合材料进行了动态拉伸试验。试验时,试样通过环氧胶和杆夹层粘接,试样的应变分别按照Hopkinson杆一维应力波理论计算和试样上应变计直接准确测量得到。结果证明:对小变形碳纤维复合材料,按一维应力波理论计算的应变与试样上直接所测应变值偏差超过100%;对较大变形的GFRP和KFRP层合板,两者偏差小于40%。说明采用Hopkinson杆一维应力波理论计算的试样应变不准确。为修正不准确性,一是通过大量数据分析建立按一维应力波理论计算值与直接测量应变之间的关系式,用此式可使此试验装置获得有效的试样应变;二是借助ABAQUS有限元模拟分析得出粘胶层以及试样过渡弧段的变形,用一维应力波理论计算的应变减去此变形,也可获得有效的试样应变。 相似文献
8.
Marie-Noëlle BussacPierre Collet Gérard Gary Ramzi Othman 《Journal of the mechanics and physics of solids》2002,50(2):321-349
When using a classical SHPB (split Hopkinson pressure bar) set-up, the useful measuring time is limited by the length of the bars, so that the maximum strain which can be measured in material testing applications is also limited. In this paper, a new method with no time limits is presented for measuring the force and displacement at any station on a bar from strain or velocity measurements performed at various places on the bar. The method takes the wave dispersion into account, as must inevitably be done when making long time measurements. It can be applied to one-dimensional and single-mode waves of all kinds propagating through a medium (flexural waves in beams, acoustic waves in wave guides, etc.). With bars of usual sizes, the measuring time can be up to 50 times longer than the time available with classical methods. An analysis of the sensitivity of the results to the accuracy of the experimental data and to the quality of the wave propagation modelling was also carried out. Experimental results are given which show the efficiency of the method. 相似文献
9.
A. M. Neville 《Applied Scientific Research》1960,9(1):71-84
Summary Test data on the recovery of creep of mortar specimens made with different cements are presented. It is shown that, whereas
creep depends on the strength of mortar (as influenced by the cement), the creep recovery is not a function of this strength.
From measurements on the change in weight of specimens, under load and free-standing, it is concluded that creep is not caused
by the movement of water from the cement paste into the surrounding medium. The possibility of creep being connected with
the removal of zeolitic water from calcium silicate hydrates is discussed, and reasons for the non-reversible character of
creep recovery are suggested. 相似文献
10.
Lower bounds on the rupture times of steadily loaded solid circular torsion bars are shown to agree well with values of the rupture times computed using an iterative procedure for different constitutive and damage laws. Corresponding to the lower bound rupture time a single reference stress can be defined for the structure. Multi-axial rupture effects are included in determining a lower bound rupture time and simple statements are made regarding structural performance and different types of material behaviour. The mode of expression of the Kachanov damage parameter in the calculation method is shown to be unimportant. Good agreement is shown between the prediction method and the results of experiments conducted on bars prepared from different materials. 相似文献
11.
Hans Broberg 《International Journal of Solids and Structures》1978,14(12):959-970
Possible sources of the observed scatter in creep deformation and rupture time are discussed. The scatter due to random material properties in creep is considered.A constitutive equation describing these random material properties is formulated. The rupture time of a specimen under constant load is calculated using Hoff s theory of ductile rupture. Rupture is shown to occur at finite elongation, in contrast to Hoff's original analysis.The probability distribution of the rupture time is determined with extremum value analysis and compared with experimentally observed ones. 相似文献
12.
为研究不同参数下表面内嵌纤维筋加固后T 形混凝土梁的破坏模式, 对5 根不同梁端锚固、FRP(fiber reinforced polymer) 筋表面特征和FRP 筋类型的T 形混凝土梁进行受弯性能试验. 结果表明, 无梁端锚固、光圆GFRP (glass fiber reinforced polymer) 筋和CFRP (carbon fiber reinforced polymer) 筋加固梁试件发生粘结破坏. 梁端锚固和FRP 筋表面特征影响加固梁试件的极限载荷, CFRP 筋加固梁试件的屈服载荷和极限载荷较大. 螺纹FRP 筋和有梁端锚固加固梁试件FRP 筋利用率较高. 因此, 有梁端锚固的表面内嵌螺纹GFRP 筋加固是最为有效的加固方式. 相似文献
13.
基于74mm直径分离式Hopkinson杆(SHPB)实验平台进行了混凝土杆的一维应力层裂实验.采用超高速相机(采样频率:2 $\mu$s/frame)结合数字图像相关法(DIC),记录混凝土试件中的动态位移场实时变化情况,探讨了混凝土在拉伸断裂过程中的表面位移场及速度场演化规律.针对实验中出现的多重层裂现象,基于一维应力波传播理论,指出各个位置在发生层裂时,其最大拉应力均由透射压缩波与反射拉伸波叠加而成,各处层裂发生时均处于一维应力状态.并提出了根据层裂位置左右两点速度趋势变化判断层裂发生时刻的判据.该判据可以给出所有层裂的起裂时间,结合DIC分析直接给出了混凝土多重层裂应变.结果显示混凝土的拉伸强度具有明显的应变率效应,在30 s$^{-1}$的应变率下,其拉伸强度的动态增强因子(DIF)可以达到5.与传统的波叠加法和自由面速度回跳法相比,DIC全场分析法不受加载波形限制,可以精确给出每个层裂的位置和起裂时间,从而得到试件在高应变率加载下不同位置处的断裂应变、拉伸强度及相应应变率,提高了测量效率. 相似文献
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A series of dynamic and static tensile-splitting experiments were performed on concrete and granite specimens to investigate the effect of induced damage on their tensile strength. These experiments were performed as part of a larger effort investigating the penetration process into the two materials. The strain rate each specimen was subjected to remained constant for these experiments, while the level of induced damage was increased. Damage was induced into the specimens through repeated drop-weight impacts and quantified using a statistical technique. The dynamic splitting experiments were performed using a split Hopkinson pressure bar (SHPB), while the static splitting experiments were conducted per the ASTM standard procedures D3967 and C496. As part of the investigation, photoelastic dynamic tensile-splitting experiments were also performed to establish the validity of using static relations for the determination of dynamic tensile strength. The experiments showed that the static splitting strength was highly dependent on the orientation of the induced damage with regard to the applied loading; however the dynamic tensile strength decreased with increasing damage with no apparent dependency on the random damage orientation. Photoelastic experiments have shown that the mechanism of failure changes for the dynamically tested damaged specimens, reducing their dependence on damage orientation. 相似文献
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18.
受拉钢筋混凝土构件破坏过程的数值模拟 总被引:1,自引:0,他引:1
采用三维材料破坏过程分析MFPA3D系统,对钢筋混凝土构件轴心受拉条件下的受力、变形与内部裂纹萌生、扩展及最终破坏全过程进行了数值试验研究。数值模型中引入统计分布函数反映了混凝土的非均匀性影响,并采用具有残余强度的弹性损伤本构模型及其破坏单元材料性质退化方法,利用位移加载方式对钢筋混凝土构件实施拉伸加载。通过对钢筋、素混凝土方形体以及钢筋混凝土方形柱体构件在拉伸作用下破坏过程的数值试验,分析了钢筋与混凝土两种材料之间的相互作用、约束机理和破坏机理。数值试验成果对于深入了解钢筋和混凝土的联合受力规律和钢筋在开裂前后对整体钢筋混凝土结构的作用机制有参考价值。 相似文献
19.
The paper is concerned with the problem of predicting nonlinear creep strains and time to ductile rupture of prismatic rods
under constant tension. The material of the rod is assumed isotropic, homogeneous, and perfectly plastic. The problem is solved
using models that take into account the change in the geometry of the rod during creep, the finiteness of the creep strains,
and the effect of the initial and actual elastic strains. The conditions whereby the characteristic dimension of the rod tends
to infinity and the accumulated and real strains in the viscous flow are limited are used as a failure criterion. The calculated
results are compared with experimental data for a number of steels and alloys to formulate the conditions for the ductile
rupture and embrittlement of metallic materials under uniaxial creep
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Translated from Prikladnaya Mekhanika, Vol. 44, No. 4, pp. 120–133, April 2008. 相似文献
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通过Φ57mm半穿甲弹对钢筋混凝土的垂直侵彻实验,得到了弹丸的撞靶速度、成坑深度、最大侵彻深度以及过载时程曲线等实验数据.对实验后钢筋的断裂特征进行分析,得到钢筋的典型破坏模式.将钢筋的破坏简化为弯曲+剪切断裂和弯曲+拉伸断裂这两种模式.根据混凝土侵彻模型和梁断裂失效理论,建立了刚性弹丸垂直侵彻钢筋混凝土的简化分析模型.将理论计算得到的侵彻深度、速度与过载时间历程分别与实验数据进行对比,结果表明两者吻合较好.研究表明,钢筋只对弹体侵彻过程产生局部影响,混凝土的抗侵彻阻力仍是钢筋混凝土抗侵彻阻力的主要组成部分. 相似文献