航空材料学报

INFLUENCE OF THE GRAIN ORIENTATION ON THE STRENGTH AND FRACTURE AT ELEVATED TEMPERATURE IN A DIRECTIONALLY -SOLIDIFIED SUPERALLOY,DZ5

Ni Hengfei, Zhang Guohuan, Yan Minggao

1981, 1(2): 1-7.

[Abstract](1524) [PDF 542KB](162)

Abstract:
The orientation dependence of the tensile and stress rupture behavior of a directionally-solidified superalloy,DZ5,has been studied.The tests were perfor-med at temperatures 700℃8 and 950℃.The real orientations of specimens were detemined by the Laue back-reflection method.The results indicated that the ten-sile strength and the stress rupture life at the temperature 700℃ were affected strongly by the orientation,however there appears no considerable effect on those properties at 950℃.As the specimen orientation deviated from the solidiea-tion direction up to 20°,the tensile strength and the stress rupture life at 700℃ were reduced dramatically.The orientation dependence can be explained success fully by schmid's law and the mechanism of the cross-slip strengthening.And the fractography analysis was made by optical and electron scanning microscope.

CHARACTERISTICS OF THE MECHANICAL PROPERTIES AND THE FRACTURES OF AN ALPHA-BETA TITANIUM ALLOY WITH DIFFERENT MICROSTRUCTURES

Ge Zhiming

1981, 1(2): 8-14.

[Abstract](1445) [PDF 500KB](153)

Abstract:
In present work,the influence of three different microstructures on the mechanical properties and the fractures of the martensite type α-β titanium alloy,Ti-6.5Al-3.5Mo-2Zr-0.3Si,was investigated.These three types of mi-crostructures are the equiaxed structure with the volume fraction of equiaxed α about 50%;the mixed structure,consisting of the nearly equiaxed α and the distorted acicular tmorphology;and the lamellar structure which consists of Widmanstatten and grain boundary α It was found that the tensile,impact, high cycle fatigue and the room temperature tensile properties after prolonged exposure at 500℃ of the equiaxed structure are superior to those of the mi-xed and lamellar structures.The highest stress-rupture and creep strength were obtained in the mixed structure which appeared to havea better combi-nation of the properties than the others.The scanning electron fractographs showed that the dimple patterns were observed in the materials with equiaxed and mixed structures.The fractures of the material with the lamellar struc-ture were characterized as the intergranular fracture with the mechanism of microvoid coalescence.

TOUGHENING EPOXY RESIN MATRIX FOR GLASS AND CARBON FIBER COMPOSITES

Ma Ruiran, Ma Manzhen, Pan Shunqing

1981, 1(2): 15-20.

[Abstract](1391) [PDF 444KB](102)

Abstract:
The reaction mechanism,microstructural feature,fracture surface morpho-logy and thermal-mechanical properties of a system consisting of butadiene-acrylonitrile rubber with radom carboxyl groups,epoxy resin of diglycidyl ether of biphenol A(DGEBA)and 2-ethyl-4-methylimidazol(EMI-2,4) were investigated. If was demostrated that DGEBA type epoxy resin can be toughened by incorporating a small amount of rubber and the toughened epoxy resin shows improved toughness without significantly decreasing thermal and mechanical properties.There may be three essential reactions occurring in the system of butadiene-aerylonitrile rubber with radom carboxyl groups and epoxy re-sin of DGEBA type in the presence of EMI-2,4.The toughened epoxy resin system is a two-phase system and each domain has an interface well bonded to the matrix.The rubbery domains in the toughened epoxy resin system can serve as nuclei for crack brenches,thus improve the toughness by dissipating the strain energy that causes the crack to propagate.

STUDY ON WELD HOT CRACKING SENSITIVITY IN CAST SUPERALLOYS K6C AND K18

Shi Changjin, Zhong Zugui, Sha Yunci, Cao Yangchu

1981, 1(2): 21-26.

[Abstract](1522) [PDF 604KB](173)

Abstract:
In this paper,two methods for weld cracking tendency determination, namely,bead-on-plate and weld-circle tests on the restrained plates were used to study the effect of welding heat input and different kinds of filler wires on weld hot cracking in cast Ni-base superalloys K6C and K18.The tempera-ture ranges which are sensitive to hot cracking were also measured.The ca-uses of weld cracking formation in the two alloys was revealed by metallo-graphic analysis.Finally,some effective measures to improve weld hot cra-cking sensitivity were recommended.

AN EVALUATION OF OVERLOAD MODELS ON THE RETARDATION BEHAVIOR IN A Ti-6Al-4V ALLOY

Gu Mingcla, Zhang Yongkui, Yan Minggao

1981, 1(2): 27-34.

[Abstract](1431) [PDF 763KB](165)

Abstract:
Overload retardation behavior under different overload ratios and different crack lengths in a Ti-6Al-4V titanium alloy has been investigated.The effect of some major factors on retardation behavior is discussed.The retardation behavior can be considered as the results of interaction effects between overload and cyclic loads.It is suggested the retardation process may be divided into five stages.From an analysis of the modes of fatigue fractures, the overloading process of fatigue crack growth in these tests can be regarded as mainly in a plane strain condition or a mixed mode in which the plane strain occurs predominantly.Thus,at a given overload ratio Qo1the number of delay cycles No caused by an overload increases with a decrease of Ko1under plane strain condition. In this paper,the Wheeler,Willenborg,Maarse,and Matsuoka models were selected in view of engineering application.An evaluation of the describ-ing capacity and life prediction of these models on retardation behavior have been made.The Matsuoka model based on the crack closure concept was found comparatively to be in good agreement with the experimental results.It is also recognized that the experimental values of overload delay effect zone size are considerably greater than the calculated values suggested by theabove mentioned models.

THE ⊿Kth AND da/dN OF LY-12CS ALUMINUM ALLOY IN BOTH 3.5% NaCl SOLUTION AND LABORATORY AIR

Mu Zaiqin, Yin Huazi, Tian Tiezhong, Xie Sishi

1981, 1(2): 35-42.

[Abstract](1432) [PDF 489KB](144)

Abstract:
The threshold △Kthand the fatigue-crack-growth rate da/dN were inves-tigated with LY-12CS aluminum in both 3.5% NaCl Salution and laboratory air.Three load ratios R were selected.That is R=0,0.33,0.67.The results showed that the △Kthfor the case of 3.5% NaCl solution was apparently lower than that in laboratory air However,the da/dN for 3.5% NaCl solution was found to be 1.6 to 3.4 times higher than that in air when the stress in-tensity range △K increased from 7 to 15kg/mm3/2for all three load ratios. In addition,△Kthtends to decrease and da/dN increase with increasing load ratio(or average stress)for both experimental environments.

A STUDY OF LOW-CYCLE THERMAL FATIGUE BEHAVIOR OF THE SUPERALLOYS GH36 AND GH132

Hao Fengxiang, Wang Haiqing

1981, 1(2): 43-50.

[Abstract](1331) [PDF 628KB](168)

Abstract:
In this paper,the performances of elevated temperature low-cycle fatigue and thermal fatigue of two superalloys GH36 and GH132 are discussed. From experimental measurement of two types of fatigue,some comparable results have been obtained.These experimental results may be considered as a theoretical base for the material selection and designing of components of turboengins.An approach to expiess the crack growth at high temperature by J-intergral had been made,and some material constants used in the for-mula are reported.

FRACTURE ANALYSIS OF COMPOSITE MATERIALS

Yang Bingxian

1981, 1(2): 51-58.

[Abstract](1358) [PDF 486KB](239)

Abstract:
In this paper some problems of fracture mechanics of composite materials are discussed.If the composite materials can be treated as homogeneousani-sotropic,parameters of fracture mechanics,such as stress intensity factor (K)or strain energy release rates(G)and Rice's J integral can be used just as that in metals.The singularity of stress fields is also r-1/2 and Jinte-gral is also path independent as that in metals.But when the composite ma-terials are treated as inhomogeneous,the expression of the stress intensity factor and the singularity of stress fields are quite different from that of homogeneous metals,and they are dependent on the position of the crack tip. The path independency of the Rice's J integral is not assured when the crack is in an inhomogeneous composite materials.By introducing a re-defined J integral,the path independency can be retained.

INVESTGATION OF X-RAY QUANTITATIVE PHASE ANALYSIS METHOD

Sheng Deguan, Yang Chengyue, Zhao Rufen

1981, 1(2): 59-67.

[Abstract](4210) [PDF 559KB](141)

Abstract:
According to Alexander's relation between diffraction intensity and weight fraction,two new calculation equations of x-ray quantitative phase analysis are obtained.According to these equations,two new methods of quntitative phase analysis are established,that is the method with reference sample and the method without standard sample.One of them can be used in the phase analysis without determined phases which are used as standard sample.Therefore,the problem to obtain pure phase is solved.The other can be used in the phase analysis sample, in such a case internal standard samples are not necessaty.The experimental operations,therefore,can be simplified and the determination accuracy can be improved.

EVALUATING THE CADMIUM EMBRITTLEMENT IN STEEL USING ACOUSTIC EMISSION

Deng Rihong, Peng Juying

1981, 1(2): 68-88.

[Abstract](1408) [PDF 7327KB](80)

Abstract:
This paper describes the application of acoustic emission to the study of cadmium embrittlement in steel.The experimental results show that the fracture of cadmium embrittlement is delay.The relationship among crack nucleation,crack growth and acoustic emission properties are tried to be found. The fracture mechanism of cadmium embritllement in steel is discussed.

1981 Vol. 1, No. 2