Technology of secondary purification by means of short-cycle unheated adsorption

Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 2, pp. 39–40, February, 1995.     

Numerical simulation of prestrain history effect on ductile crack growth in mismatched welded joints

Pipe reeling may lead to plastic pre‐deformation (prestrain) around existing cracks in components; therefore, investigating whether this process accelerates or counteracts ductile crack growth, especially for strength mismatched welded joints, is warranted. This study focused on the effect of prestrain history on ductile crack growth in mismatched welded joints. A single‐edge‐notched tension specimen was selected for numerical study, and the crack was assumed to have existed before a prestrain history was applied. Crack growth resistance curves for plane strain and mode I crack growth under large‐scale yielding conditions have been computed using the complete Gurson model. Meanwhile, symmetrical and non‐symmetrical prestrain cycle modes with different loading levels were applied to the overmatched specimens. The outcome demonstrated that the mismatch ratio (the ratio between the yield stress of the weld metal and base metal) showed a significant effect on fracture resistance regardless of the stage at which the prestrain cycle loading was located. By contrast, the processing of the crack growth was weakened by the increase of prestrain values, and the symmetrical prestrain cycle resulted in greater plastic damage than the non‐symmetrical prestrain cycle did. However, the initial crack length had a non‐significant effect on the ductile fracture considering the prestrain and mismatch effects.     

Fracture investigation of U‐notch made of tungsten–copper functionally graded materials by means of strain energy density

The averaged strain energy density over a well‐defined control volume was employed to assess the fracture of U‐notched specimens made of tungsten–copper functionally graded materials under prevalent mode II loading. The boundary of control volume was evaluated by using a numerical method. Power law function was employed to describe the mechanical properties (elasticity modulus, Poisson's ratio, fracture toughness and ultimate tensile stress) through the specimen width. The effect of notch tip radius and notch depth on notch stress intensity factors and mode mixity parameter χ were assessed. In addition, a comparison based on fracture load between functionally graded and homogeneous W–Cu was made. Furthermore, in this research, it was shown that the mean value of the strain energy density over the control volume can be accurately determined using coarse meshes for functionally graded materials.     

Analytical modelling of residual stress in additive manufacturing

A physics‐based analytical model to assess residual stresses in additive manufacturing made of metallic materials is presented and validated experimentally. The model takes into consideration the typical multi‐pass aspect of additive manufacturing. First, the thermal signature of the process is assessed by predicting the temperature for the problem of a moving heat source, then, the thermally induced stresses in a homogenous semi‐infinite medium are determined. Taking the thermal stresses as input, the residual stresses are calculated analytically to obtain the distribution across the depth. Good agreement is obtained between the analytical prediction and X‐ray measurements made on Selective Laser Melted 316L Stainless Steel. In addition, the analytical approach enables in‐depth interpretations of results with basis in the true mechanisms of the process. Thus, the present model appears as a promising tool for optimization of process parameters in additive manufacturing, which in turn will improve the understanding of process parameters and their effect on properties of the final product.     

Some Expressions for the Strain Energy in a Finite Volume Surrounding the Root of Blunt V-notches

The paper gives some closed form expressions for the strain energy averaged in a finite size volume surrounding the root of blunt V-shaped notches under Mode I loading. The control volume, reminiscent of Neuber’s concept of elementary structural volumes, is thought of as dependent on the ultimate tensile strength and the fracture toughness K_IC in the case of brittle or quasi-brittle materials subjected to static loads. Expressions for strain energy density under plane strain conditions and Mode I loading have been derived from an analytical frame recently reported in the literature, which matches Williams and Creager-Paris’ solutions in the particular cases of plates weakened by sharp V-notches or blunt cracks (U-notches), respectively. In order to validate a local-strain-energy based approach, a well-documented set of experimental data recently reported in this journal by Gómez and Elices has been used. Data refer to blunt and sharp V-specimens of PMMA subjected to static tension loads and characterised by a large variability of notch root radius (from 0 to 4.0 mm) and notch angle (from 0° to 150°). Critical loads obtained experimentally have been compared with the theoretical ones, estimated here by keeping constant the mean value of the strain energy in a well-defined small size volume.     

The proton iron-sulfur cluster environment of the [FeFe]-hydrogenase maturation protein HydF from Thermotoga neapolitana

[FeFe]-hydrogenases contain a complex [4Fe–4S]-2Fe cluster (H-cluster) and are able to efficiently reduce protons to H₂. Due to their potential exploitation for renewable energy production biotechnologies, significant efforts have been put into understanding the mechanisms driving the H-cluster assembly, which involves three conserved proteins. Among them, HydF works as scaffold upon which the H-cluster precursor is synthesized and carrier to deliver it to the hydrogenase, resulting in its activation. A FeS cluster binding sequence (CxHx₄₆-₅₃HCxxC) is conserved in all HydF proteins and should in principle provide four ligands to coordinate the Fe atom. However, we found that alternative metal coordination may exist in different HydF proteins and that only the three cysteines are strictly required, whereas the fourth ligand may vary and is, in any case, readily exchangeable. In this work we analyzed by EPR/HYSCORE the FeS cluster proton environment of HydF from Thermotoga neapolitana to determine the possible role of surrounding residues in the non-cysteinyl iron ligation of the protein.     

On Higher Order Terms in the Crack Tip Stress Field

The influence of higher order terms on the stress field of a cracked plate under in plane loading may not be negligible in some engineering applications. The aim of this note is to present a more accurate analysis of these terms.     

Some new practical equations for rapid calculation of J-integral in plates weakened by U-notches under bending

The paper deals with calculations of the J-integral for a plate weakened by U-notches under Mode I bending loading in the case of a material obeying a linear elastic law. The main aim of the study is to suggest some new equations suitable for calculations of the J-integral under bending loading. Although some closed-form solutions exist in the literature based on elliptic integrals, some expressions, simple to be implemented, are useful as a rapid engineering tool.