Material Related Phenomena Research Articles

Thermostat Influence on the Structural Development and Material Removal during Abrasion of Nanocrystalline Ferrite.

We consider a nanomachining process of hard, abrasive particles grinding on the rough surface of a polycrystalline ferritic work piece. Using extensive large-scale molecular dynamics (MD) simulations, we show that the mode of thermostating, i.e., the way that the heat generated through deformation and friction is removed from the system, has crucial impact on tribological and materials related phenomena. By adopting an electron-phonon coupling approach to parametrize the thermostat of the system, thus including the electronic contribution to the thermal conductivity of iron, we can reproduce the experimentally measured values that yield realistic temperature gradients in the work piece. We compare these results to those obtained by assuming the two extreme cases of only phononic heat conduction and instantaneous removal of the heat generated in the machining interface. Our discussion of the differences between these three cases reveals that although the average shear stress is virtually temperature independent up to a normal pressure of approximately 1 GPa, the grain and chip morphology as well as most relevant quantities depend heavily on the mode of thermostating beyond a normal pressure of 0.4 GPa. These pronounced differences can be explained by the thermally activated processes that guide the reaction of the Fe lattice to the external mechanical and thermal loads caused by nanomachining.

A fully generalised approach to modelling fire response of steel–RC composite structures

A three-step model for the performance-based numerical simulations of the fire response of steel–RC two-layered beam-like composite structures is presented and validated. The first step consists of the determination of the evolution of temperatures in the structure׳s surroundings. Moisture and the heat transfer through the RC layer and the conduction of heat over the steel layer are obtained in the second step. In concrete, the transfer of water vapour, dry air, and free water is discussed as well as the evaporation and liquefaction phenomena and the dehydration of concrete and its thermal and mechanical degradation. Within the framework of the third step, a geometrically and materially non-linear mechanical response of the structure is proposed accounting for interlayer slips and uplifts as well as for various material-related phenomena such as the material hardening/softening and creep. The governing equations are solved numerically. An efficient, novel strain-based finite element formulation is introduced for the mechanical analysis. Due to its generality and consideration of several different possible non-linear material, geometrical, and interlayer contact phenomena and their couplings the model can be of a use to a broader fire science community for exploring the impact of different physical parameters on the results of the addressed numerical simulations, thereby providing directions for further research. In the paper a case of such a study is also demonstrated exploring the contribution of the steel sheet and the flexibility of the interlayer connection of a standard trapezoidal steel–RC slab to its ultimate fire resistance. A reasonable contribution of the sheet is proved if the stiffness ratio between the integrated and the external tensile reinforcement of the RC plate is low provided that the contact connection is sufficiently stiff.

The development of the ICME supply-chain: Route to ICME implementation and sustainment

Over the past twenty years, integrated computational materials engineering (ICME) has emerged as a key engineering field with great promise. Models simulating materials-related phenomena have been developed and are being validated for industrial application. The integration of computational methods into material, process and component design has been a challenge, however, in part due to the complexities in the development of an ICME “supply-chain” that supports, sustains and delivers this emerging technology. ICME touches many disciplines, which results in a requirement for many types of computational-based technology organizations to be involved to provide tools that can be rapidly developed, validated, deployed and maintained for industrial applications. The need for, and the current state of an ICME supply-chain along with development and future requirements for the continued pace of introduction of ICME into industrial design practices will be reviewed within this article.

Kohonen mapping of the crack growth under fatigue loading conditions of stainless steels in BWR environments and of nickel alloys in PWR environments

In this study, crack growth rate data under fatigue loading conditions generated by Argonne National Laboratories and published in 2006 were analyzed [O.K. Chopra, B. Alexandreanu, E.E. Gruber, R.S. Daum, W.J. Shack, Argonne National Laboratory, NUREG CR 6891-series ANL 04/20, Crack Growth Rates of Austenitic Stainless Steel Weld Heat Affected Zone in BWR Environments, January, 2006; B. Alexandreanu, O.K. Chopra, H.M. Chung, E.E. Gruber, W.K. Soppet, R.W. Strain, W.J. Shack, Environmentally Assisted Cracking in Light Water Reactors, vol. 34 in the NUREG/CR-4667 series annual report of Argonne National Laboratory program studies for Calendar (Annual Report 2003). Manuscript Completed: May 2005, Date Published: May 2006], and reported by DoE [B. Alexandreanu, O.K. Chopra, W.J. Shack, S. Crane, H.J. Gonzalez, NRC, Crack Growth Rates and Metallographic Examinations of Alloy 600 and Alloy 82/182 from Field Components and Laboratory Materials Tested in PWR Environments, NUREG/CR-6964, May 2008]. The data collected were measured on austenitic stainless steels in BWR (boiling water reactor) environments and on nickel alloys in PWR (pressurized water reactor) environments. The data collected contained information on material composition, temperature, conductivity of the environment, oxygen concentration, irradiated sample information, weld information, electrochemical potential, load ratio, rise time, hydrogen concentration, hold time, down time, maximum stress intensity factor ( K max), stress intensity range (Δ K max), crack length, and crack growth rates (CGR). Each position on that Kohonen map is called a cell. A Kohonen map clusters vectors of information by ‘similarities.’ Vectors of information were formed using the metal composition, followed by the environmental conditions used in each experiments, and finally followed by the crack growth rate (CGR) measured when a sample of pre-cracked metal is set in an environment and the sample is cyclically loaded. Accordingly, one experiment will result in a long vector of data containing information such as [Fe, wt%], [Cr, wt%], [Temperature, T], [Electrochemical potential, ECP], [ K max], [Conductivity, k], [CGR], etc. In that long data-vector, CGR is only one component of the vector. To ‘increase’ the importance of the CGR over the other components of the data-vectors, ‘functional links’ or functions of the CGR (as powers, logarithms, etc.) are added to each one of the vectors, resulting in longer vectors. The trained Kohonen map cells adopt ‘average’ values from all of the vectors stored in that cell. Accordingly, each Kohonen cell is ‘represented’ by and ‘average’ vector. The ‘average’ vectors representing each one of the Kohonen trained cells are topologically arranged on the map surface; i.e. ‘high crack growth rates’ vectors are stored on cells far apart of ‘low crack growth rates’ cells. Each of the parameters forming the vector can be investigated; maps of the trends of each parameter were drawn and those maps were compared to the maps of the CGRs. This paper presents the results by means of 3-dimensional figures that show the beneficial and detrimental effects that each of the variables considered has on the CGR on austenitic stainless steel weld heat affected zones in BWR environments and on nickel alloy welds in PWR environments. Data-mining methodologies (including clustering analysis) are useful to extract information from data. ‘Nuclear waste’ belongs to a category of subjects that are extremely complicated, mainly because many electrochemical and material-related phenomena can occur simultaneously. Stress corrosion cracking can be present among the corrosion problems faced by nuclear waste storage. The data-mining on ‘the effect of material composition and environment on the CGRs’ (presented in this paper – in our knowledge used by first time in the area of nuclear waste) is to be used by the reader as an example of a methodology that can be adopted for other problems encountered in the nuclear waste industry and for which data are available.