A Criterion of Local Strength

We propose a local criterion of brittle strength for structurally inhomogeneous materials based on the size effect of mechanical properties of materials under the conditions of stress concentration. It is assumed that the function of local strength of the material depends on the scaling factor equal to the ratio of the size of the zone of stress concentration to the characteristic structural size of the material. We study the problem of strength of a solid body containing a stress concentrator of any size and shape in tension, including the limiting case of degeneration of a smooth concentrator into a rectilinear (or circular) crack. The requirements to the behavior of the critical stress and critical size of the defect are formulated and the form of the function of local strength is specified. For the fracture stress, we deduce interpolation-type expressions and compare the obtained numerical results with the available experimental data.     

金属材料断裂准则研究进展

介绍了金属材料断裂准则的研究进展,包括传统强度理论、现代断裂力学理论及常用断裂准则,并对各种准则的特点进行了简要分析。     

陶瓷材料可靠性分析中的统计断裂强度理论

评述了当前陶瓷材料统计断裂强度理论的发展概况,分析了两种建立强度分布方程的统计方法,探讨了它们用于陶瓷材料可靠性分析和陶瓷部件设计的可行性.并基于对缺陷的尺度分布和方位分布以及裂纹扩展路径不规则性的统一考虑,理论分析了一般应力状态下陶瓷材料的统计断裂强度.     

基于GISSMO断裂准则的6016铝合金断裂行为研究

目的 研究零部件在成形与碰撞过程中,6016铝合金在不同应力状态下的断裂行为。方法 通过准静态拉伸实验,获得了6016铝合金的基本力学性能。利用Nakajima成形极限实验,获得了6016铝合金材料的断裂成形极限曲线。设计了7种涵盖成形及碰撞过程中应力状态的断裂极限测试试样,采用数字图像相关技术(DIC)记录了试样在变形过程中的全场应变。利用实验-有限元反求方法标定了6016铝合金的GISSMO断裂准则的参数,并用帽形件三点弯曲实验验证了模型的合理性。结果 相比于传统断裂成形极限图的预测结果,基于GISSMO断裂准则的仿真结果与实验具有更好的一致性。结论 所建立的GISSMO模型可以用于预测6016铝合金在复杂应力状态下的断裂行为。     

High-cycle Fatigue Fracture Behavior of Ultrahigh Strength Steels

The fatigue fracture behavior of four ultrahigh strength steels with different melting processes and therefore different inclusion sizes were studied by using a rotating bar two-point bending fatigue machine in the high-cycle regime up to 107 cycles of loading. The fracture surfaces were observed by field emission scanning electron microscopy （FESEM）. It was found that the size of inclusion has significant effect on the fatigue behavior. For AtSI 4340 steel in which the inclusion size is smaller than 5.5 μm, all the fatigue cracks except one did not initiated from inclusion but from specimen surface and conventional S-N curve exists. For 65Si2MnWE and Aermet 100 steels in which the average inclusion sizes are 12.2 and 14.9 μm, respectively, fatigue cracks initiated from inclusions at lower stress amplitudes and stepwise S-N curves were observed. The S-N curve displays a continuous decline and fatigue failures originated from large oxide inclusion for 60Si2CrVA steel in which the average inclusion size is 44.4 pro. In the case of internal inclusion-induced fractures at cycles beyond about 1×10^6 for 65Si2MnWE and 60Si2CrVA steels, inclusion was always found inside the fish-eye and a granular bright facet （GBF） was observed in the vicinity around the inclusion. The GBF sizes increase with increasing the number of cycles to failure Nf in the long-life regime. The values of stress intensity factor range at crack initiation site for the GBF are almost constant with Nf, and are almost equal to that for the surface inclusion and the internal inclusion at cycles lower than about 1×10^6. Neither fish-eye nor GBF was observed for Aermet 100 steel in the present study.     

Strength and Fracture Behavior of Ultrathin Pt Wires

Ultrathin metallic wires having defects may show much lower strength compared to the strength of the wire material. To characterize ultrathin Pt wires having the nominal diameter of 625 nm, tensile test of the wires was performed by developing a testing platform and a gripping technology. Fracture stress determined by the tensile test showed much higher value compared with that of bulk Pt. However, the fracture stress of some of the wires was lower than the yield stress of the wire determined by the bending test. From the observation of the fracture surfaces, it was found that the lower fracture stress of the wires was due to the defects in the wires and such wires showed brittle fracture behavior.     

应变能密度比准则在块体非晶合金中的应用

由于块体非晶合金独特的原子排列结构,导致其具有独特的力学行为。多年来,国内外研究人员对块体非晶合金的断裂行为进行了一系列的研究,并取得了一定的成果。本文简单介绍了近年来国内外针对块体非晶合金断裂准则的研究状况,随后比较全面地介绍了应变能密度比失效准则,并推导了遵循该准则时断裂角θT(载荷方向与断裂面的夹角)与α(断裂面剪应力与正应力的比值)应满足的关系,最后利用Zr41.2Ti13.8Cu10.0Ni12.5Be22.5块体非晶合金的拉伸实验和已有的实验结果,证实了块体非晶合金遵循应变能密度比失效准则。     

Cleavag Fracture Criterion of Low Alloy Steal and Weld Metal in Notched Specimens

The cleavage fracture criterion of low alloy steel and weld metal in notched specimens is investigated in detail based on a great number of experimental data. It has been found that the most cleavage fractures initiate at a distance shorter (left side) than that of the peak stress location below a notch root, and the cleavage fracture in notched specimens must satisfy a dual criterion, i.e., a critical plastic strain (ε_p ≥ ε_pc) for initiating a crack nucleus, and a critical tensile stress (σ_yy ≥ σ_f) for its propagation. According to the dual criterion model, the great number of experimental data of 4PB (four-point bending) tests for the low alloy steel and weld metal and their statistical distribution are explained. The effects of temperature , the local fracture stress σ_f and the critical plastic strain ε_pc on the locations of cleavage initiation sites and the controlling steps of cleavage fracture process are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

断裂故障研究中裂尖塑性区的影响及处理原则

通过对K判据的适用区与裂纹尖端塑性区的比较,在塑性区一定要小于K判据适用区的条件下,给出了K判据的适用边界线和判断脆性断裂的判断式;确定了K判据在结构静强度计算中塑性修正的基本原则,在此基础上讨论得出了塑性区尺寸小于裂纹长度,裂纹扩展寿命的估算方法仍适用,塑性对裂纹扩展寿命估算影响不大,而选用不同的经验公式估算裂纹扩展寿命所出现的误差却很大的结论.     

碳纤维/环氧单向复合材料的统计强度和破坏准则

本文运用了纤维损伤的随机临界核理论及混合法则 ,对碳纤维 /环氧单向复合材料受纵向拉伸时的统计强度及破坏准则作了理论分析与实验研究     

微裂纹对相变陶瓷的相变条件及强度的影响

相变临界条件的研究是相变增韧的关键，材料内大量存在的微裂纹是影响相变陶瓷性能的重要因素。本文用作者改进的等效夹杂理论，研究相变陶瓷中微裂纹对材料强度的影响，建立在外载作用下的相变临界条件。通过Ａｌ_２Ｏ_３／ＺｒＯ_２陶瓷的三点弯曲实验，验证了本文理论模型的合理性。     

Strength of a Cracked Reinforced-Concrete Element from the Viewpoint of Fracture Mechanics

We develop a procedure for the numerical analysis of T-sections of reinforced-concrete elements and evaluation of their strength and crack resistance from the viewpoint of fracture mechanics. The expressions for K _Ic and _Ic are deduced for the case of eccentric compression. The theoretical values of fracture forces are in good agreement with the experimental data and, hence, the proposed procedure can be recommended for the determination of strength and crack resistance of reinforced-concrete columns.     

Photoelectron Counting Theory in Terms of the Wigner and Q Representations of the Light Field

Abstract

We show how to present the standard theory of photoelectron counting in terms of the Wigner and Q representations of the light field.     

On the Statistical Theory of Long-Term Strength of Glass

We present new methods for the evaluation of the statistical parameters of long-term strength of glass and describe the procedure of preparation of specimens (glass disks) for testing, the method of loading, and the experimental procedure. The statistical model of fracture of glass is presented and the conclusions concerning the evaluation of the parameters of strength are made.__________Translated from Problemy Prochnosti, No. 3, pp. 75 – 85, May – June, 2005.     

Express-Method of Ranking of Polymer Materials by Energy Criterion Identification of Fracture Mode

Strength of Materials - To provide the functional adequacy, aesthetic qualities, and durability of the process of restoration of the elements of the dentofacial system, it is required to have the...