共查询到20条相似文献,搜索用时 15 毫秒
1.
Galip Said Halil Aytekin 《Fatigue & Fracture of Engineering Materials & Structures》2013,36(7):640-649
One of the fundamental aims of fracture mechanics is to define fracture toughness KIC of a material. Hence, the ASTM E399 standard was developed. However according to the standard, large‐sized specimens are required to determine the fracture toughness of low alloy carbon steels. ASTM E1921 standard was developed on the fracture toughness of ferritic steels. In this study, a new method was proposed to determine the fracture toughness of ferritic steels. The purpose of the present paper is to compare the results of the method with the experimental results. Two steels that are used in gas and oil main pipelines were investigated in this study. 相似文献
2.
A method combining experimental and finite element analysis is developed to determine interlaminar dynamic fracture toughness. An interlaminar crack is propagated at very high speed in a double cantilever beam (DCB) specimen made of two steel strips which are bonded together by epoxy with a precrack of about 40 mm length. The face of the front cantilever is bonded to a large solid block and a special fixture is designed to apply impact load to the rear cantilever through a load bar. In the load bar, a compressive square shaped elastic stress pulse is generated by impacting it with a striker bar which is accelerated in an air gun. The rear cantilever is screwed to the load bar; when the incident compressive pulse reaches the specimen, a part of the energy is reflected into the load bar and the rest of it passes to the specimen. By monitoring the incident and the reflected pulses in the load bar through strain gauges, deflection of cantilever-end is determined. The crack velocity is determined by three strain gauges of 0.2 mm gauge length bonded to the side face of the rear cantilever. Further, the first strain gauge, bonded very close to the tip of the precrack, and the crack velocity determine the initiation time of crack propagation.
The experimental results are used as input data in a finite element (FE) code to calculate J-integral by the gradual release of nodal forces to model the propagation of the interlaminar crack. The initiation fracture toughness and propagation fracture toughness are evaluated for an interlaminar crack propagating with a velocity in the range of 850 to 1785 m/s. The initiation toughness and propagation toughness were found to vary between 90–200 J/m2 and 2–13 J/m2, respectively. 相似文献
3.
4.
L.M. Barker 《Engineering Fracture Mechanics》1977,9(2):361-369
A fracture toughness measuring concept is presented which is based on the use of specimen configurations for which the initial crack growth is stable under controlled force (“soft” machine) conditions. The concept is analyzed, and is demonstrated on a specimen configuration consisting of a short rod with narrow longitudinal slots for crack guides. Tests were conducted on two types of aluminum, PMMA, fused quartz and siltstone rock. It is shown that the fracture toughness test is very simple to perform, gives repeatable results, and is equally applicable to both ductile and brittle materials. 相似文献
5.
A. E. PIOTROWSKI M. J. O'Brien 《Fatigue & Fracture of Engineering Materials & Structures》2006,29(7):558-572
A novel mechanical test has been developed to measure the fracture toughness of the silicon‐nitride (Si3N4) balls used in modern hybrid bearings. The ball is compressed diametrally between two hemispherical conforming dies, which causes the ball's equator to bulge, generating a tensile hoop stress. Under applied load, a precrack placed at the equator grows. To calculate the ball's fracture toughness at crack instability, finite‐element calculations of the applied stress field and an analytical solution for the stress intensity factor are used in the ‘two point plus semiellipse’ method. Tests of 16 Si3N4 balls and three soda‐lime glass balls gave fracture toughness measurements in good agreement with accepted published values. The new technique appears to be more accurate than the indentation technique used to measure the toughness of ceramics. As future work, the test can be extended to measure fatigue and stress corrosion properties for Si3N4 balls. 相似文献
6.
Qi-Zhi Wang 《International Journal of Fracture》1997,85(3):231-240
A sandwich three-point bend specimen has recently been proposed to test mode-I interlaminar fracture toughness for fiber-reinforced
composite materials. The test composite consist of a thin layer bonded by two lateral reusable steel bars (Sohn et al. 1995).
Some time earlier this specimen configuration was used to test fracture toughness of adhesives (Zdaniewsk et al. 1987). However,
formulae for analysing its fracture mechanics parameters such as stress intensity factor and energy release rate can not be
found in the literature. The lack of adequate formulae may explain why suitable quantitative analysis using this specimen
configuration has not been achieved. In this paper, a simple and effective homogenisation method is used to change the bi-material
system, which represents the specimen, into single uniform test material. This physical homogenisation is carried out by geometric
change of the cross section of lateral steel parts based on equal deflection rigidity. For the transformed specimen configuration
of single uniform material, the corresponding stress intensity factor solution from handbooks is available. Two formulae of
stress intensity factor for the sandwich three-point bend specimen are given as upper limit and lower limit respectively,
they are plotted with varying elastic tensile modulus mismatch. Then the relation between stress intensity factor and energy
release rate, with special consideration of orthotropy of the tested composite material, is used to derive its energy release
rate. The specimen and its formulae can also be applied to test other materials such as wood, welded joints (Burstow and Ainsworth,
1995), as well as to test dynamic fracture toughness.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Ebrahim M. Shaji Surya R. Kalidindi Roger D. Doherty Aleksandar S. Sedmak 《Materials Science and Engineering: A》2003,340(1-2):163-169
The multiphase alloy MP35N (35% Ni, 35% Co, 10% Mo, 20% Cr) is a high strength, high toughness alloy of choice for several safety-critical applications in aerospace, oil drilling, and biomedical industries. Several previous attempts in literature to measure the plane strain fracture toughness of commercially drawn MP35N did not produce reliable values since they violated one or more of the criteria stipulated by ASTM standards for a valid measurement of KIc. In most cases, the requirements for plane strain and small scale yielding conditions were not met, since the commercially drawn material was available only with limited cross-sectional dimensions. In this investigation specially designed specimens (modified compact tension (CT) specimens) have been used to measure the plane strain fracture toughness of MP35N in both the unaged and the aged conditions. The KIc of the commercially drawn (53% reduction level) MP35N was measured to be 126 MPa√m, while that of the commercially drawn and aged MP35N was measured to be 98 MPa√m. Both these measurements satisfied all the required criteria stipulated by ASTM standards for valid measurements of KIc. The new procedure used in this study has been verified by the measuring of fracture toughness of Al alloy, using both the modified specimen, as designed here, and the standard one. The results for plane strain fracture toughness of MP35N alloy have been verified by the standard measurement of JIc values for both the aged and the unaged alloys. Finally, on a suitably normalized plot, introduced in this paper, the toughness-strength envelop for MP35 is higher than most of structural alloys, but significantly lower than that of the TRIP steels. 相似文献
8.
9.
Jamal Bidadi Javad Akbardoost Mohammad Reza Mohammad Aliha 《Fatigue & Fracture of Engineering Materials & Structures》2020,43(2):277-291
Study of the thickness effect in predicting the crack growth behavior and load bearing capacity of rock‐type structures is an important issue for obtaining a relation between the experimental fracture toughness of laboratory subsized samples and the real rock structures with large thickness. The fracture of rock masses or underground rock structures at deep strata may be dominantly governed by the tensile or tear crack growth mechanism. Therefore, in this research, a number of mode I and mode III fracture toughness experiments are conducted on edge notch disc bend (ENDB) specimen made of a kind of marble rock to investigate the effect of specimen thickness on the corresponding KIc and KIIIc values. It is observed that the fracture toughness of both modes I and III are increased by increasing the height of the ENDB specimen. Also, the ratio of KIIIc/KIc obtained from each thickness of the ENDB specimens is compared with those predicted by some fracture criteria, and it was shown that the minimum plastic radius (MPR) criterion is the main suitable criterion for investigating the fracture toughness ratio KIIIc/KIc . Also, the effect of ENDB height on fracture trajectory of tested samples is assessed. It is shown that the crack grows curvilinearly in thicker ENDB samples and cannot extend along the crack front in small specimens. 相似文献
10.
11.
12.
A stable correlation between the material fracture toughness characteristics and statistical parameters of scatter of hardness
values has been established.
__________
Translated from Problemy Prochnosti, No. 6, pp. 5–12, November–December, 2007. 相似文献
13.
为了研究2A14T6铝合金焊接接头(焊缝/熔合线/热影响区/母材)的低温(77K/4.2K)断裂韧性,采用表面裂纹法,通过自主研制的低温位移传感器及力学测试系统得到了断裂韧性KIQ性能参数,并结合断口具体分析了形貌与断裂韧性的关系。研究结果表明:该测试系统能够有效的测量材料的低温表面裂纹断裂韧性KIQ;无论在室温还是低温下,焊接接头不同区域的断裂韧性大致为母材〉热影响区〉熔合线〉焊缝;除熔合线变化不明显外,各区域的断裂韧性随温度的降低而增加,呈现较好的规律性;微观断口形貌与断裂韧性试验测试结果有较好的一致性。 相似文献
14.
15.
V. T. TROSHCHENKO 《Fatigue & Fracture of Engineering Materials & Structures》2009,32(4):287-291
The paper considers the peculiarities of fatigue crack propagation and final fracture of metals under cyclic loading. It is shown that the value of the fatigue fracture toughness of steels in an embrittled state is appreciably lower than that of the fracture toughness under static loading. A model of the transition from stable to unstable fatigue crack propagation is justified. 相似文献
16.
17.
The application of peel tests for the measurement of adhesive fracture toughness of metal-polymer laminates is reviewed and the merits of a mandrel peel method are highlighted. The mandrel method enables a direct experimental determination of both adhesive fracture toughness (GA) and the plastic bending energy (GP) during peel, whilst other approaches require a complex calculation for GP. In this method, the peel arm is bent around a circular roller in order to develop a peel crack and an alignment load attempts to ensure that the peel arm conforms to the roller.The conditions for peel arm conformance are thoroughly investigated and the theoretical basis for conformation are established. Experimental investigations involve the study of the roller size (radii in the range 5-20 mm are used), the peel arm thickness (varied from 0.635 to 2.0 mm) and the magnitude of the alignment load. In addition, the plane of fracture is studied since fractures can vary from cohesive to interfacial and this has a profound influence on the value of GA and on interpretation of results.A test protocol for conducting mandrel peel is developed such that the roller size for peel arm conformance can be established from preliminary fixed arm peel tests.The work is conducted on two epoxy/aluminium alloy laminates suitable for aerospace applications. Comparative results of adhesive fracture toughness from mandrel peel and multi-angle fixed arm peel are made with cohesive fracture toughness from a tapered double cantilever beam test. 相似文献
18.
The validity of a statistical method for estimating an engineering lower bound fracture toughness in the ductile-to-brittle transition region is investigated using the Euro fracture toughness dataset generated in the European SM&T Project “Fracture Toughness of Steel in the Ductile-to-Brittle Transition Regime”. The lower bound method is based on the empirical evidence that, in the low probability regime, the cumulative failure probability function tends to be a straight line rather than a curve as is the case for Weibull distributions. The investigation demonstrates that the engineering lower bound toughness values as predicted by the method are related to a cumulative cleavage failure probability lower than 2.5%. Such bound predictions can be achieved on the basis of a small number of cleavage toughness values measured at the temperature of interest. The results confirm the validity of the method. 相似文献
19.
A new testing procedure is suggested for measuring the fracture toughness of brittle materials as superconductors and ceramics. The idea is to perform a compression test on a subcompact square specimen which contains a central hole. The presence of the hole induces a tensile stress at a certain small region attached to the hole. In this region an artificial notch is introduced such that the fracture path satisfies a pure tensile opening mode (mode I) to which the linear fracture mechanics rules apply. The stress distribution on the fracture plane guarantees a certain amount of stable crack extension. The relationship between the critical compressive load and the stress intensity factor is formulated via an available Green function along with a numerical solution (FEM with ANSYS code). The testing procedure is demonstrated with specimens made of two types of tungsten carbide which differ by their grain size only. Test results are examined via fracture toughness and strength values produced by other conventional methods and the agreement is very good. The geometry and loading direction enable the fracture toughness results to be relatively insensitive to the notch tip radius and the crack length, thereby relaxing the requirements for accurate measurements.The small size of the suggested specimen (12.70mm×12.70mm×5mm) and the avoidance of gripping interfaces provide the major cost-wise advantages. 相似文献
20.
Effect of compressive transverse normal stress on mode II fracture toughness in polymeric composites
Effect of transverse normal stress on mode II fracture toughness of unidirectional fiber reinforced composites was studied
experimentally in conjunction with finite element analyses. Mode II fracture tests were conducted on the S2/8552 glass/epoxy
composite using off-axis specimens with a through thickness crack. The finite element method was employed to perform stress
analyses from which mode II fracture toughness was extracted. In the analysis, crack surface contact friction effect was considered.
It was found that the transverse normal compressive stress has significant effect on mode II fracture toughness of the composite.
Moreover, the fracture toughness measured using the off-axis specimen was found to be quite different from that evaluated
using the conventional end notched flexural (ENF) specimen in three-point bending. It was found that mode II fracture toughness
cannot be characterized by the crack tip singular shear stress alone; nonsingular stresses ahead of the crack tip appear to
have substantial influence on the apparent mode II fracture toughness of the composite. 相似文献