Estimate of Coffin–Manson Curve Shift for the Porous Alloy AlSi9Cu3 Based on Numerical Simulations of a Porous Material Carried Out by Using the Taguchi Array

In real engineering applications, machine parts are rarely completely homogeneous; in most cases, there are at least some minor notch effects or even more extensive inhomogeneities, which cause critical local stress concentrations from which fatigue fractures develop. In the present research, a shift of the Coffin–Manson εa–N material curve in a structure with random porosity subjected to dynamic LCF loads was studied. This allows the rest of the fatigue life prediction process to remain the same as if it were a homogeneous material. Apart from the cyclic σ–ε curve, which is relatively easy to obtain experimentally, the εa–N curve is the second most important curve to describe the correlation between the fatigue life N and the strain level εa. Therefore, the correct shift of the εa–N curve of the homogeneous material to a position corresponding to the porous state of the material is crucial. We have found that the curve shift can be efficiently performed on the basis of numerical simulations of a combination of five porosity-specific geometric influences and the associated regression analysis. To model the modified synthetic εa–N curve, five geometric influences of porosity by X-ray or μ-CT analysis are quantified, and then the porosity-adjusted coefficients of the Coffin–Manson equation are calculated. The proposed approach has been successfully applied to standard specimens with different porosity topography

Predicting the Fatigue Life of an AlSi9Cu3 Porous Alloy Using a Vector-Segmentation Technique for a Geometric Parameterisation of the Macro Pores

Most of the published research work related to the fatigue life of porous, high-pressure, die-cast structures is limited to a consideration of individual isolated pores. The focus of this article is on calculating the fatigue life of high-pressure, die-cast, AlSi9Cu3 parts with many clustered macro pores. The core of the presented methodology is a geometric parameterisation of the pores using a vector-segmentation technique. The input for the vector segmentation is a μ-CT scan of the porous material. After the pores are localised, they are parameterised as 3D ellipsoids with the corresponding orientations in the Euclidian space. The extracted ellipsoids together with the outer contour are then used to build a finite-element mesh of the porous structure. The stress–strain distribution is calculated using Abaqus and the fatigue life is predicted using SIMULIA fe-safe. The numerical results are compared to the experimentally determined fatigue lives to prove the applicability of the proposed approach. The outcome of this research is a usable tool for estimating the limiting quantity of a structure’s porosity that still allows for the functional performance and required durability of a product

Influence of inhomogeneity clusters to fatigue life of dye-casted products

Pri obravnavi ulitkov se večina dosedanjih raziskav omejuje le na vpliv posameznih, izoliranih por. Ta doktorska naloga se zato osredotoča na slabše raziskano področje vpliva obsežne makro poroznosti na dobo trajanja. Gre za celovito raziskavo pogosto uporabljene aluminijeve zlitine v livarski industriji AlSi9Cu3. Pomemben segment raziskav predstavlja opis ugotovljenih makro poroznih defektov, tj. por in hladnih spojev, s tehniko z voksli, ki je nato primerjana še z alternativno tehniko opisa defektov z vektorsko segmentacijo. Povratni inženiring poroznosti je izveden na osnovi µ-CT posnetkov in nato uporabljen za numerični izračun dobe trajanja po teoriji malociklične trdnosti, s komercialnim paketom SIMULIA (Abaqus in fe-safe). Študija služi kot pomoč pri oceni, kdaj so odlitki lahko še uporabni in kdaj so tveganja za hitre iniciacije poškodb zaradi prisotnih por prevelika. Skozi analize lahko primerjamo različne metalurške defekte in dobimo vpogled, kateri bolj in kateri manj vplivajo na znižanje dinamične nosilnosti. V raziskave so vključene tudi eksperimentalno-teoretične primerjave zdržljivosti različnih celičnih struktur z negativnim Poissonovim razmerjem iz zlitine Al7075-T651. Skupni rezultati kažejo na pridobitev koristnih novih orodij, ki jih lahko uporabimo pri ocenjevanju tako urejenih kot tudi naključnih poroznih struktur, ali te še vedno omogočajo funkcionalno delovanje in zahtevano trajnost izdelka.When dealing with casted parts most research to this date is limited to the influence of individual and isolated pores. This doctoral dissertation therefore focuses on the less researched area of the influence of large-scale macro porosity on fatigue life. It is a comprehensive study of commonly used aluminium alloy in the foundry industry AlSi9Cu3. An important segment of research is a description of the identified macroporous defects, i.e. pores and cold shuts with the voxel technique, which is then compared with the alternative technique of defect description using a vector segmentation technique. By applying a reversed engineering the porosity is modelled on the basis of μ-CT scans and then used for the numerical calculation of the fatigue life according to the theory of low-cyclic fatigue with the commercial SIMULIA software (Abaqus and fe-safe). The study serves as an aid in assessing when castings parts may still be useful and when the risks of rapid initiation of fatigue damage due to the pore clusters present are too great. Through analyses, different metallurgical defects can be compared and estimated which defects have greater and which less effect on the reduction of fatigue life. Experimental-theoretical comparisons of the durability of different cellular structures with a negative Poisson ratio from the Al7075-T651 alloy are also included in the research with an objective to first test the proposed methodology on the cases of regular geometric inhomogeneities. The overall results indicate the acquisition of useful new tools that can be used to assess both the ordered and random porous structures, in order to assess whether these still allow functional operation and the required fatigue life of the product

Prediction of static and low-cycle durability of porous cellular structures with positive and negative Poisson\u27s ratios

The static and low-cycle durability of three planar cellular structures, hexagonal, auxetic and auxetic-chiral, have been compared. The three structures have the same critical cross-section and are made from an aluminium alloy Al7075-T651. The reference region of each structure is represented by a matrix of nine elementary shaped cells (3 rows by 3 columns). For each structure static and low-cycle fatigue experiments at different loading amplitudes were made. Numerical simulations were then performed for the same boundary conditions to predict the static and low-cycle fatigue durability. For this purpose a continuum damage mechanics approach with element removal was used in explicit dynamic simulations. The results of static simulations were also checked using the eXtended Finite Element Method (XFEM). All the numerical simulations were carried out using Abaqus. Good agreement was observed between the simulated and measured results for each of the three cellular structures

Estimate of Coffin–Manson curve shift for the porous alloy AlSi9Cu3 based on numerical simulations of a porous material carried out by using the Taguchi array

In real engineering applications, machine parts are rarely completely homogeneousin most cases, there are at least some minor notch effects or even more extensive inhomogeneities, which cause critical local stress concentrations from which fatigue fractures develop. In the present research, a shift of the Coffin–Manson ε$_a$–N material curve in a structure with random porosity subjected to dynamic LCF loads was studied. This allows the rest of the fatigue life prediction process to remain the same as if it were a homogeneous material. Apart from the cyclic σ–ε curve, which is relatively easy to obtain experimentally, the ε$_a$–N curve is the second most important curve to describe the correlation between the fatigue life N and the strain level ε$_a$. Therefore, the correct shift of the ε$_a$–N curve of the homogeneous material to a position corresponding to the porous state of the material is crucial. We have found that the curve shift can be efficiently performed on the basis of numerical simulations of a combination of five porosity-specific geometric influences and the associated regression analysis. To model the modified synthetic ε$_a$–N curve, five geometric influences of porosity by X-ray or µ-CT analysis are quantified, and then the porosity-adjusted coefficients of the Coffin–Manson equation are calculated. The proposed approach has been successfully applied to standard specimens with different porosity topography

Predicting the fatigue life of an AlSi9Cu3 porous alloy using a vector-segmentation technique for a geometric parameterisation of the macro pores

Most of the published research work related to the fatigue life of porous, high-pressure, die-cast structures is limited to a consideration of individual isolated pores. The focus of this article is on calculating the fatigue life of high-pressure, die-cast, AlSi9Cu3 parts with many clustered macro pores. The core of the presented methodology is a geometric parameterisation of the pores using a vector-segmentation technique. The input for the vector segmentation is a µ-CT scan of the porous material. After the pores are localised, they are parameterised as 3D ellipsoids with the corresponding orientations in the Euclidian space. The extracted ellipsoids together with the outer contour are then used to build a finite-element mesh of the porous structure. The stress–strain distribution is calculated using Abaqus and the fatigue life is predicted using SIMULIA fe-safe. The numerical results are compared to the experimentally determined fatigue lives to prove the applicability of the proposed approach. The outcome of this research is a usable tool for estimating the limiting quantity of a structure\u27s porosity that still allows for the functional performance and required durability of a product

Improved prediction of low-cycle fatigue life for high-pressure die-cast aluminium alloy AlSi9Cu3 with significant porosity

The fatigue life of a high-pressure die-cast alloy, AlSi9Cu3, with significant porosity is investigated. Standard specimens were cyclically loaded (R =-1) until fatigue rupture occurred. The specimens were [micro]-CT scanned to obtain a 3D representation of the pores. Models were used to computationally predict the fatigue life using two different methods. First, the fatigue life was predicted using a notch-strain approach combined with a Coffin- Manson durability relationship for homogeneous material. Second, the fatigue life was predicted using an homogenised un-notched model that was combined with an adapted Coffin-Manson relationship which consid-ered a fatigue life reduction due to different pore effects.Raziskava zajema analizo dobe trajanja zlitine AlSi9Cu3 s prisotno visoko stopnjo poroznosti. Preizkušanci standardnih oblik so bili ciklično obremenjeni (R = -1), do nastalega utrujenostnega loma. Vzorci so bili ob tem [mikro]-CT skenirani, da smo določili 3D geometrijo por. Modeli so bili nato uporabljeni pri izračunu dobe trajanja po dveh različnih metodah. Prvič, dobo trajanja smo napovedali po pristopu z zareznim učinkom v kombinaciji s Coffin-Manson razmerjem za homogeni material. Drugič, dobo trajanja smo napovedali ob uporabi homogenega idealiziranega modela, v kombinaciji s prilagojenim nivojem Coffin-Manson krivulje, ki upošteva znižanje dobe trajanja zaradi različnih učinkov por

Durability prediction of cyclically loaded CP-W800 fillet welds

Two methods of durability prediction of fillet welds were researched in this study. Namely, the structural Hot-Spot method and the structural stress method fe-safe Verity were applied to fatigue life estimation of a double plate lap fillet weld made of high-strength complex phase CP-W800 steel. Durability predictions were compared against available high-cycle fatigue experimental data obtained for the same weld detail and material. Both 2D and 3D finite element meshes were considered in the simulations. It was shown that comparable predictions were obtained using either the Hot-Spot method or the fe-safe Verity module in the case of the 3D FE mesh. On the contrary, a less conservative durability prediction was observed using the Hot-Spot method and a more conservative durability prediction was gained using the fe-safe Verity module in the case of the 2D FE mesh due to a different consideration of stress concentration around the weld