摘要:

Abstract—Several surface cold work procedures are developed to induce compressive residual stresses adjacent to a notch in a flat element. It would appear that they should all lead to fatigue life enhancement. For sharp notched specimens excellent fatigue life enhancement is observed. For moderately notched specimens only one of the procedures produces this enhancement. In order to shed light on the shortcomings of two of the procedures, the residual stress field is determined by means of finite element analyses in two and three dimensions. It is observed that the two‐dimensional analyses predict a residual stress field which should lead to fatigue life enhancement. It is the three‐dimensional analyses which help to explain why two of the cold work procedures

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00779.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Fatigue crack growth in an α+β titanium alloy (TA6V) with three microstructural conditions is studied in high vacuum at 300°C. The faster growth rates are observed in the material with a low content of primary α phase and a fine equiaxed microstructure. Near the threshold regime, a slow crystallographic Stage I‐like propagation is observed in the three microstructural types where slip occurs along a single‐plane system which develops within the α grains. These crystallographic facets are identified using an electron backscattering pattern (EBSP) technique and were found to lie on ba

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00780.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—A hypothesis on the statistical relation between the local microscopic directions of fatigue crack growth and the macroscopic crack front shape is postulated. The method of fractographic reconstitution of the fatigue crack front shape from local microscopic directions of crack growth is proposed and tested in two different application

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00781.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The use of a load spectrum in airframe fatigue life predictions is considered. In‐service fatigue lives are predicted using a probabilistic approach that takes into account the main aspects of deterministic methods. Expressions are derived for damage under fixed flight‐hours together with data scatter. The influence of material fatigue properties on scatter are shown. An algorithm for obtaining simple formulae for accounting for equivalent airframe fatigue conditions are demonstrated. An example is given for deriving a safe fatigue life distribution fun

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00782.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Fatigue tests were carried out on welded T‐joints of JIS A5083P‐O Al‐Mg alloy under constant amplitude and superimposed random load waves. Each random wave was generated by superimposing a secondary zero‐mean random process on a constant amplitude pulsating trapezoidal wave, which simply simulated the GAG (ground‐air‐ground) stress cycles, or on a constant d.c. (direct current) component. It is proved that the 1‐dimensional rainflow method is insufficient as the mean stress effects are not considered. From a procedure using a 2‐dimensional rainflow method and the original and a modified Goodman diagram, it was concluded that the mean stress effects on secondary waves are larger in the case of GAG than d.c. Considering this, a life estimation procedure is proposed that gives consistent and acceptable e

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00783.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00784.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The criteria for determining whether ferritic material exhibits fully ductile behaviour are generally based on the fracture toughness vs temperature relationship determined from standard laboratory test pieces (e.g. Charpy V Impact tests or fracture toughness specimens). This relationship defines a ductile‐brittle transition region. When fully ductile, microvoid coalescence behaviour is experienced, and fracture toughness is described as being on the “upper shelf”. At “off the shelf” temperatures brittle, cleavage fracture is experienced. On the lower shelf the material is entirely brittle, exhibiting 100% crystallinity on the fracture face. As the temperature increases, initiation of tearing by microvoid coalescence occurs and some stable tearing can occur prior to the cleavage event. Material toughness increases with temperature until the upper shelf condition is achieved.The characteristics of fracture toughness tests in terms of the toughness level exhibited and the extent of ductile tearing experienced have been used as a guide to whether the structural application (e.g. a pressure vessel) will behave in a brittle or a ductile manner. This paper reports on a feasibility study where various worked examples have been performed to examine the concept of using a “cut off” on the failure assessment diagram, determined from the conditions required to cause plastic collapse of a pressure vessel, as a criterion for defining effective “ductile” operation. Fracture assessment procedures (R6 revisions 2 and 3 and PD6493 levels 2 and 3) have been utilised to determine the influence on pressure vessel performance of the behaviour of fracture toughness test specimens.The procedure of plotting a structural collapse “cut off” on a failure assessment diagram enables the assessment of whether a particular flaw geometry would result in gross deformation of the structure at failure. The use of this procedure provides an unambiguous demarcation between “fracture dominated” and “collapse controlled” conditions. This procedure facilitates judgements on the level of toughness necessary to ensure ductile operation and whether a “tearing plus toughness” requirement is necessary.It is recommended that consideration be given to including structural collapse into fracture assessment procedures carried out using R6 revision 3 or PD 6493:1991 procedures in order to determine the conditions when enhanced toughness no longer influences structural performance (i.e. when effective “

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00785.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The paper discusses the results of fatigue crack growth rate tests conducted in the presence of residual stresses. Three different residual stress distributions, obtained by laser welds, were employed in order to characterize the crack propagation behaviour under different conditions, producing either an increase or a reduction of the stress intensity factor due to external loads. Test results are analysed by means of a non‐linear numerical model (based on the weight function method) and a knowledge of the fatigue crack growth properties of the base material, free from residual stresses. The results of the analysis are discussed with reference to experimental trends, in order to clarify the predictive capabilities of the method and aspects needing further investigat

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00786.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—An efficient and accurate method for computing the fatigue‐life distribution of metal structures is presented. The problem is governed by the basic equations of the Coffin‐Manson‐Neuber local‐strain fatigue theory for notched components. The coefficients of fatigue strength and fatigue ductility, the fatigue notch factor as well as the nominal‐stress amplitude may be random variables with an arbitrary joint distribution. In order to arrive at a direct solution for the fatigue‐life distribution, hence an assessment of the reliability of a component, a collocation method has been developed which gives the total‐strain amplitude as an explicit function of the stress amplitude and the fatigue notch factor. This explicit equation has very close conformity to the corresponding, true, implicit equation. The fatigue‐life distribution is finally expressed in a multiple‐integral closed form. A simple algorithm termed the “complete‐probability fast integration” (CPFI) is developed which gives the exact solution, to any desired accuracy, for the entire ranges of fatigue‐life and reliability. CPFI is superior when compared to the results and procedures of the approximate

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00787.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The initiation and propagation of fatigue cracks in an Al‐Li 8090 alloy in a vapour environment of 0.6 M NaCl solution was investigated. A severe degradation of the resistance to short crack growth was exhibited. Preliminary work carried out to establish the susceptibility of the material to hydrogen embrittlement demonstrated a close correlation between the deformation mode of this alloy and hydrogen absorption. The combination of highly localized slip and highly localized hydrogen fugacity creates a high susceptibility to hydrogen‐assisted crack growth.On the basis of current micro‐mechanical models, it is suggested that hydrogen trapping induces a reduction of the friction stress acting in the crack tip plastic zone. Consequently, enhanced plasticity at the crack tip due to the decrease in friction stress leads to an increase in crack growth rate.An exact solution for a surface crack in a semi‐infinite plane is obtained based on a dislocation crack model. Using this solution a computer method is developed to calculate the time‐dependent short crack growth rate and fatigue lifetime. Both solutions show good correspondence with the experimen

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00788.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY