Initial Structure Of Material Research Articles

Characterisation of Fibre Bundle Deformation Behaviour—Test Rig, Results and Conclusions

Deformation of continuous fibre reinforced plastics during thermally-assisted forming or joining processes leads to a change of the initial material structure. The load behaviour of composite parts strongly depends on the resultant material structure. The prediction of this material structure is a challenging task and requires a deep knowledge of the material behaviour above melting temperature and the occurring complex forming phenomena. Through this knowledge, the optimisation of manufacturing parameters for a more efficient and reproducible process can be enabled and are in the focus of many investigations. In the present paper, a simplified pultrusion test rig is developed and presented to investigate the deformation behaviour of a thermoplastic semi-finished fiber product in a forming element. Therefore, different process parameters, like forming element temperature, pulling velocity as well as the forming element geometry, are varied. The deformation behaviour in the forming zone of the thermoplastic preimpregnated continuous glass fibre-reinforced material is investigated by computed tomography and the resultant pulling forces are measured. The results clearly show the correlation between the forming element temperature and the resulting forces due to a change in the viscosity of the thermoplastic matrix and the resulting fiber matrix interaction. In addition, the evaluation of the measurement data shows which forming forces are required to change the shape of the thermoplastic unidirectional material with a rectangular cross-section to a round one.

Thermodynamics and Structural Properties of Ti3SiC2 in Liquid Lead Coolant

It has been investigated by molecular dynamics method the effect of oxygen injection for Ti3SiC2 corrosion inhibition when this material immersed into high temperature liquid lead coolant. The diffusion coefficient of Ti3SiC2 was determined from mean-square-displacement simulation data. The structures of Ti3SiC2 during corrosion inhibition using oxygen agent were observed by Ovito vizualisation code. The simulations have been done using the Moldy molecular dynamics code. Initial material structure as input of simulation generated by Atomsk, Packmol and VESTA codes based on “file 1520829.cif” format file that taken from the crystallography open database (CoD) website. It is from our work we can show that injecting oxygen with concentration about 0.15 – 0.19 wt%, it seems can stabilize the structure of Ti2SiC3 maximally.

Phase Dynamics on Conversion-Reaction-Based Tin-Doped Ferrite Anode for Next-Generation Lithium Batteries.

The conventional view of conversion reaction is based on the reversibility, returning to an initial material structure through reverse reaction at each cycle in cycle life, which impedes the complete understanding on a working mechanism upon a progression of cycles in conversion-reaction-based battery electrodes. Herein, a series of tin-doped ferrites (Fe3- xSn xO4, x = 0-0.36) are prepared and applied to a lithium-ion battery anode. By achieving the ideal reoxidation into SnO2, the Fe2.76Sn0.24O4 composite anchored on reduced graphene oxide shows a high reversible capacity of 1428 mAh g-1 at 200 mA g-1 after 100 cycles, which is the best performance of Sn-based anode materials so far. Significantly, a newly formed γ-FeOOH phase after 100 cycles is identified from topological features through synchrotron X-ray absorption spectroscopy with electronic and atomic structural information, suggesting the phase transformation from magnetite to lepidocrocite upon cycling. Contrary to the conventional view, our work suggests a variable working mechanism in an iron-based composite with the dynamic phases from iron oxide to iron oxyhydroxide in the battery cycle life, based on the reactivity of metal nanoparticles formed during reaction toward the solid electrolyte interface layer.

Structural Transformations on the Surfaces of Epoxy Composite–Steel Tribological Pair

The modern problems of tribotechnical material science are considered; in particular, the selforganization in polymer composites has been studied. It is established that steady-state selective transfer reduces the wear rate of an epoxy composite material. It is confirmed that it can be used in partial or zero lubrication conditions. The self-organization processes that occur in polymer composites during tribological interaction determine the suitability of a system to be used as a selflubricating material. In friction, the determining factor is not only the initial material structure, but also the surface layer structure formed according to the load–speed operating mode.

Loading history and structure of fracture of material

The bearing capacity of the structured materials and features of their fracture depend on local reaction of elements of structure on loading history. The initial structure of material can be modified in the course of prefracture at the initial stage of loading such that at further deformation, including deformation with the changed ratio of loadings on axes, this induced structure determines the scenario of fracture of material and its strength. The effective strength of heterogeneous materials and scenarios of their fracture are influenced by the level of the intermediate main stress. At compression of a cracked body lack of significant reaction to stresses along the sliding plane is characteristic for initial microcracks (areas of sliding). In a porous body such effect is absent. Therefore at tests with the proportional mode of loading according to the Karman or Böker schemes the effective measured strength can differ.To estimate an influence of a type of initial structural elements – pores and microcracks - on a final phase of fracture at uniaxial compression within a plane problem, an approach based on their equivalence to action of some concentrated forces is used. If the main crack is formed by joining a system of microcracks – the sliding areas, the movement on which causes the wedging forces, then weakening of the action in the process of the main crack growth is small. In case of a porous structure an influence of pores, remote from the crack tip, on the effective stress intensity factor KI in the process of crack sizes increasing weakens much faster. Therefore in a porous body development of echelons of rather short cracks joining small number of pores (N ~ 2-3) is energetically preferable, while occurring of the main cracks is characteristic for a cracked body at a final stage of fracture at compression. For a body with microcracks in which after coalescence of cracks from two and more concentrators the stress intensity factors for the formed defect become larger than it was at the moment of microcracks coalescence, the choice of the fracture scenario – development of the main fault occurs at the initial stage of fracture.In the porous body, forming the cracks with an influence of pores, favorable conditions for initiation of fracture in the new source of fracture at the small size of cracks are only created near the crack tips. The induced structure of fracture arising at partial unloading also influences the fracture mechanism at the subsequent loading. Development of a system of the feathering of cracks in the vicinity of the main fault also belongs to such structures. The last can be used as a method for the main crack arresting.

Simulation of Stress and Strain for Induction-Hardening Applications

The possibility to manage stress and strain in hardened parts might be beneficial for a number of induction-hardening applications. The most important of these benefits are the improvement of fatigue strength, avoidance of cracks, and minimization of distortion. An appropriate and powerful way to take the stress and strain into account during the development of a process is to make use of computer simulations. In-house developed and commercial software packages have been coupled to incorporate the electromagnetic task into the calculations. The simulations have been performed followed by analysis of the results. The influences of two different values of quenching intensity, strength of initial material structure, strength of austenite, surface power density-frequency-time combination, and workpiece diameter on the residual stress are studied. The influence of quenching intensity is confirmed by the series of experiments representing the external hardening of a cylinder with eight variations of quenching intensity. Measured by x-rays, the values of surface tangential stress are used as a dataset for verification of the model being used for analyses.

Material metric, connectivity and dislocations in continua

In this paper, we present a framework within which the role of the initial material structure of a body, or its developing structure in the course of deformation, is accounted for in the constitutive equation of the material. The problem is dealt with at the local level, i.e., at the material neighborhood. If a neighborhood has structure then its geometry cannot be represented by a Euclidean metric. The entire body may thus be non–Euclidean. We formulate the constitutive equation for large deformation in the case where either a neighborhood is non–Euclidean because of its initial structure, or it becomes so by virtue of irreversible internal motion and/or induced dislocation fields, which we discuss at some length. In the formulation of the theory, questions of connectivity arise and are dealt with in the text.