Untitled

Borbély, András; Mughrabi, H.; Eisenmeier, G.; Höppel, Heinz Werner

doi:10.1023/a:1016350528652

Cited by 46 publications

(11 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…10b). The origin location -close or at the surface -offers highest stress concentration due to superposition of the stress fields of the single particles and the free surface [21]. This effect may be influenced by high compressive stresses, which possibly result in the absence of near-surface crack origins.…”

Section: Fatigue Crack Initiationmentioning

confidence: 99%

Influence of surface residual stresses on gigacycle fatigue response of high chromium cold work tool steel

Sohar¹,

Betzwar-Kotas

Gierl

et al. 2008

Materialwissenschaft Werkst

View full text Add to dashboard Cite

The effect of surface compressive residual stresses (RS) induced by surface grinding and polishing on the gigacycle fatigue behavior of medium-carbon high-chromium alloy cold work tool steel was evaluated. Two test series were performed: Specimens of series I revealed high compressive RS of about -800 MPa at the surface, resulting from grinding with fine emery paper, which treatment had definitely a beneficial influence on the fatigue endurance strength. The existence of surface RS was also revealed to be responsible for the location of the fatigue crack initiation. High compressive RS favored internal crack origins. In this case crack nucleation sites were primary carbide clusters in the interior of the specimen, forming so-called fish-eyes at the fracture surface. In contrast, specimens of test series II had only very low RS, which enabled crack initiation near/at the surface at primary carbides/clusters. Furthermore, it has been shown that the high initial RS are prone to partial relaxation through cyclic loading for which the mechanisms are currently unknown. In this case near-surface induced failure was obtained. It was possible to confirm the experimentally obtained data by the use of the concept of local fatigue strength as function of effective RS. The relaxation of high initial RS was experimentally confirmed through RS measurements at runout specimens (10 10 cycles without failure

show abstract

Section: Fatigue Crack Initiationmentioning

confidence: 99%

Influence of surface residual stresses on gigacycle fatigue response of high chromium cold work tool steel

Sohar¹,

Betzwar-Kotas

Gierl

et al. 2008

Materialwissenschaft Werkst

View full text Add to dashboard Cite

show abstract

“…Besides, given the complexity of implementing the FE calculation, an effort will be made to derive an analytic criteria to estimate the stress concentration level based on the 3D characteristics of individual pores (r,d, shape, etc.) as suggested by Borbely et al [13]…”

Section: Discussionmentioning

confidence: 63%

“…[13] This stress level is responsible for the activation of plasticity which leads to crack initiation. In order to check this assumption, FE calculations based on a realistic 3D microstructure have been performed as described in the following paragraph.…”

Section: Pore Distribution Analysismentioning

confidence: 99%

“…In summary, correlation between fatigue properties and pore characteristics becomes possible when the whole distribution of pores in the samples is taken into account; the distance of pore from surface d and its equivalent size r seem to be two important parameters to consider as they have a direct influence on the local stress level in the vicinity of the pore. [13] This stress level is responsible for the activation of plasticity which leads to crack initiation. In order to check this assumption, FE calculations based on a realistic 3D microstructure have been performed as described in the following paragraph.…”

Section: Pore Distribution Analysismentioning

confidence: 99%

See 1 more Smart Citation

3D Characterization of the Influence of Porosity on Fatigue Properties of a Cast Al Alloy

et al. 2010

View full text Add to dashboard Cite

Because of their high strength to weight ratio, their low processing cost and their ability to be cast in intricate shapes, cast aluminum alloys are widely used in the automotive industry to produce block engines. However, this kind of material always contains pores when no special casting technique is used (between 0.1 and 25% of porosity depending on the process used and the shape of the resulting product). This porosity has a detrimental influence on the mechanical properties. For instance a value as low as 1% (volume fraction) of porosity can lead to a reduction of 50% of the fatigue life and 20% of the fatigue limit compared with the same alloy with a similar microstructure but showing no pores. [1] To correlate fatigue properties of cast Al alloys to the presence of porosity, one can classically study the fracture surfaces of broken fatigue samples in a scanning electron microscope, in order to identify which defect(s) is (are) responsible for crack initiation. However, the main drawback of fractographic studies is that they only reveal the weak link within the pore distribution. When the tail of the distributions matters, as it is the case in fatigue, comparisons with other samples remains qualitative. [2,3] In this study, samples made of an A380 cast alloy were tested in fatigue. A standard fractographic study was carried out on broken samples to determine the size and position of the defect(s) responsible for the fracture. The threedimensional (3D) distribution of pores in the fatigue samples was determined by X-ray tomography. This information was used to establish correlations between the number of cycles to fracture and the whole pore distribution in the sample. Finite element (FE) computations, based on the 3D tomographic images, have also been used to estimate the stress level around pores taking into account their position, size, and shape. Materials and MethodsThe studied material is an A380 alloy (85.8% of aluminum; 8.9% of silicon; 3.1% of copper; 0.7% of zinc; 0.2% of manganese and magnesium; 0.1% of lead, iron, nickel, titanium, chromium, and tin each less than 0.1%-all in wt%). The samples were produced by permanent mold casting as used in the automotive industry for the production of car engines. Based on radiographic inspection, the samples were classified in three categories according to their pore content. Class A corresponds to the lowest volume faction of porosity (below grade 1 of the ASTM E505 standards) and class C to the highest (grade 2 of the ASTM E505 standards). In the present paper only results on the median class are presented (class B -grade 1 of the ASTM E505 standards).The 0.2% yield strength of the Al cast material is 90 MPa and its tensile strength 150 MPa. The fatigue tests were performed at constant stress amplitude (R ¼ À1) with a frequency of 10 Hz on hour glass specimens with a 20 mm gage length and a 5 mm diameter (Fig.

show abstract

“…Such a defect has to be subsurface (internal) so that stress concentrations will be low as shown in detailed finite-element studies. For instance, Borbely et al [23] showed that internal failure originating from pores should be limited to the ones in which defects lie close to the surface, as observed by Staley et al [24] in HIP A206 castings. Such a defect is presented in Figure 4, [17] which shows facets formed around a sand inclusion in an A356 casting.…”

Section: Fig 1-facets Observed By Nyahumwamentioning

confidence: 94%

Fracture Surface Facets and Fatigue Life Potential of Castings

Tiryakioğlu

Campbell

Nyahumwa

2011

Metall Mater Trans B

View full text Add to dashboard Cite

Fatigue potential has been studied in cast aluminum alloys with regard to the fatigue crack initiation mechanism at the casting defects, particularly surface and subsurface defects. The significance of facets is interpreted as the presence of defects in the interior of castings. Furthermore, two varieties of facets have been identified, one originating as a dendrite-straightened bifilm (type I facet) and the other originating from a slip plane mechanism around casting defects (type II facet). The fatigue life potential of castings is reexamined based on the involvement of defects during the formation of both types of facets. It is proposed that the true fatigue life potential of defect free castings has yet to be observed, i.e., if castings can be produced without defects, then their fatigue performance will be significantly higher than even the best performances observed so far.

show abstract

Untitled

Cited by 46 publications

References 6 publications

Influence of surface residual stresses on gigacycle fatigue response of high chromium cold work tool steel

Influence of surface residual stresses on gigacycle fatigue response of high chromium cold work tool steel

3D Characterization of the Influence of Porosity on Fatigue Properties of a Cast Al Alloy

Fracture Surface Facets and Fatigue Life Potential of Castings

Contact Info

Product

Resources

About