On the accuracy of nominal, structural, and local stress based approaches in designing aluminium welded joints against fatigue

This paper investigates the accuracy and reliability of nominal stresses, hot-spot stresses, effective notch stresses, notch-stress intensity factors (N-SIFs) and material length scale parameters in estimating fatigue lifetime of aluminium welded joints. This comparative assessment was based on a large number of experimental data taken from the literature and generated by testing, under either cyclic axial loading or cyclic bending, a variety of aluminium welded structural details. Whenever it was required, stress analyses were performed by solving bi-dimensional linear-elastic finite element models. The obtained results demonstrate that the effective notch stress method, the N-SIF approach, and the Theory of Critical Distances (TCD) provide a more accurate fatigue life estimation in comparison with the other methodologies. In this context, the TCD was seen to be easier to adopt, requiring less computational effort than the effective notch stress method and the NSIF approach. Finally, based on the experimental results being re-analysed, a unifying value of 0.5 mm is proposed for the TCD critical distance, with this value allowing aluminium welded connections to be designed accurately irrespective of joint geometry’s complexity

Nominal and local stress quantities to design aluminium-to-steel thin welded joints against fatigue

Welding aluminium to steel to make mechanical joints is possible, but there is, to date, no accepted method for performing the fatigue assessment of such hybrid connections. In this context, the present investigation aims at checking the accuracy of nominal stresses, effective notch stresses, notch-stress intensity factors, and the Modified Wöhler Curve method (applied in conjunction with the Theory of Critical Distances) in estimating fatigue lifetime of butt, cruciform, lap and tee aluminium-to-steel thin welded joints. EWM coldArc® welding technology was used to manufacture the welded specimens that were used for this validation exercise. The samples being tested in the structural laboratory of the University of Sheffield, UK, were manufactured by using AA1050 aluminium and EN10130:1991 steel with main plates thicknesses of 1 mm or 2 mm. The results from this experimental/theoretical investigation demonstrate that all the design methodologies being investigated can be used to perform the fatigue assessment of aluminium-to-steel thin welded joints provided that suitable reference/calibration fatigue curves are used. In the present paper, some quantitative recommendations are given for use in situations of practical interest of the design techniques being considered

On the use of hot-spot stresses, effective notch stresses and the Point Method to estimate lifetime of inclined welds subjected to uniaxial fatigue loading

The present paper addresses the problem of estimating fatigue strength of welded joints when the weld seams are inclined with respect to the direction of the applied cyclic force. From a fatigue design point of view, the main complexity lies in the fact that, with this particular welded geometries, although the applied loading is uniaxial, accurate fatigue assessment can be performed provided that the degree of multiaxiality of the nominal/structural/local stress states at the weld toes/roots is modelled effectively. To this end, in the present investigation the Modified Wöhler Curve Method (MWCM) is attempted to be used to assess the fatigue strength of steel joints with inclined welds by using this multiaxial fatigue criterion in conjunction with nominal stresses, hot-spot stresses, effective notch stresses, and the Theory of Critical Distances (TCD). A large number of experimental results taken from the literature and generated by testing inclined fillet welds was used to check the accuracy and reliability of the MWCM applied along with these different ways of determining the relevant stress states. The results obtained from this validation exercise demonstrate that the MWCM returns satisfactory estimates when it is used to assess fatigue strength in the presence of inclined welds, with this holding true independently of the specific stress analysis strategy being adopted

Static strength and design of aluminium-to-steel thin welded joints

Welding together dissimilar materials, and, in particular, aluminium alloys to steel, has always been a challenge because of the significant difference in their mechanical, thermo-physical and metallurgical properties which causes the formations of hard and brittle intermetallic phases in the welding region. Recently, EWM® has developed a welding process known as ColdArc®, where the heat input and arc stability are precisely controlled. The present study was designed to investigate the static strength of aluminium-to-steel thin welded joints manufactured using EWM coldArc® welding technology. Butt, lap and cruciform welded connections were prepared to assess tensile strength and failure mode of these hybrid welded joints. The visual examination of the fracture surfaces revealed that, regardless of the geometry of the welded connections, the fracture of the joints always took place in the heat-affected zone (HAZ) on the aluminium side. This inspection indicated that the use of EWM coldArc® welding technology had improved the strength of the hybrid welded joint significantly and removed the problem of having a brittle phase in the welding zone. The results obtained from this investigation shows that Eurocode 9 can also be used to design aluminium-to-steel thin welded joints

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018.

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field

Static and fatigue behaviour of aluminium-to-steel thin welded joints

Welding together dissimilar materials, and, in particular, aluminium alloys to steel, has always been a challenge because of the significant difference in their mechanical, thermo-physical and metallurgical properties which causes the formations of hard and brittle intermetallic phases in the welding zone [1]. Recently, EWM® had developed a welding process known as ColdArc®, where the heat input and arc stability are precisely controlled [2]. The present study was designed to investigate the static and fatigue behaviour of aluminium-to-steel thin welded joints manufactured using EWM ColdArc® welding technology. Butt, cruciform and lap hybrid welded joints (Fig.1a-c) were fabricated to study, in terms of nominal stress approach, their tensile strength as well as their fatigue behaviour

Material characteristic lengths to design 3D-printed notched titanium against fatigue

In the present paper, the Theory of Critical Distances (TCD) and the Strain Energy Density (SED) approach are attempted to be used to predict the fatigue lifetime of notched components made from additively manufactured titanium. The reliability of these two methods was checked systematically by using a large number of experimental data we generated by testing notched specimens of 3D printed titanium containing different geometrical features and tested using various loading types and stress ratios. Our methods were seen to be successful, giving predictions falling always within the scatter band of the data from the un-notched material. These results are very interesting, especially considering that both the TCD and the SED are very easy to use because they require only a linear-elastic stress analysis