Changes In Internal Strain Research Articles

Hybrid coating SnO2 for enhanced Li ions storage

Anode SnO2 in lithium-ion batteries suffers from volume expansion and agglomeration. Here, the SnO2 nanoparticles are hybrided with ZrO2 particles by the support of carbon nanotube networks. The obtained SnO2/C/ZrO2 composite shows improved electrochemical performances. Investigations reveal that the carbon nanotubes shorten the transmission path of electrons and Li+ ions. Ball milling with ZrO2 promotes the formation of nanosized SnO2 to weaken the internal strain change, being beneficial to buffering volume change during electrochemical cycling afterwards. High-resolution 6,7Li NMR investigations indicate that conversion and alloying reactions are stepwise involved for SnO2/C/ZrO2 anode. The strategy of designing SnO2/C/ZrO2 composite from the morphology-controlled metal-organic frameworks for energy storage widens the possibility to fabricate promising materials with enhanced performances.

Production of a nanocrystalline composite of Al–4% Cu/SiC by a mechanical milling method

Aluminum powders with an average particle size of 45 μm and copper with a particle size of <60 μm were used to produce a solid solution of Al–4 Cu. The effect on the formation time of solid solution and changes in internal strain and the aluminum lattice parameter of adding SiC particles to the milling was studied. The results showed that the addition of 10% SiC to the powder mixture reduced alloying of the Al–4% Cu solution from 10 to 4 h, which would accelerate the process of mechanical alloying. Moreover, when the milling time was increased to 10 h, the average size of primary crystals was reduced from 81 to 21 nm; when SiC was added to the powder mixture the crystallite size was further reduced, with the average size reaching 16 nm. The initial strain also rose from 0.18% to 0.67% and the initial strain of the powder mixture containing 10% SiC reached 0.76%. The resulting powder was evaluated by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results were used to determine the average size of the crystals, the lattice parameter and the internal strain and the SEM images were used to investigate changes in morphology, shape and particle size of the powder.

Interplay between strain, defect charge state, and functionality in complex oxides

We use first-principles calculations to investigate the interplay between strain and the charge state of point defect impurities in complex oxides. Our work is motivated by recent interest in using defects as active elements to provide novel functionality in coherent epitaxial films. Using oxygen vacancies as model point defects, and CaMnO3 and MnO as model materials, we calculate the changes in internal strain caused by changing the charge state of the vacancies, and conversely the effect of strain on charge-state stability. Our results show that the charge state is a degree of freedom that can be used to control the interaction of defects with strain and hence the concentration and location of defects in epitaxial films. We propose the use of field-effect gating to reversibly change the charge state of defects and hence the internal strain and corresponding strain-induced functionalities.

Composite cure simulation scheme fully integrating internal strain measurement

This study proposes a new approach to determine key material parameters for stress/strain calculation of curing composite laminates and validate the simulation. Specifically, fiber Bragg grating (FBG) strain sensors are embedded in a composite laminate and the two key parameters for simulation, composite shrinkage strain and stiffness change during curing, are simultaneously determined from in-situ measurements by the embedded sensors. Furthermore, the simulation is validated using internal strain change during curing. This paper begins by presenting an overview of the proposed simulation scheme and by comparing it with previous approaches to highlight its advantages. Material parameter determination using a shear-lag effect at the edge of the embedded sensors is then described and the practical procedure to obtain the key parameters is demonstrated using a carbon/epoxy laminate. Finally, cure simulation is conducted for validation. Further extension to more general cases including thermoplastic composites is also discussed.

Memorizing and detecting an arrested crack in a foam-core sandwich structure using embedded plastic materials and fiber-optic sensors

The authors recently established the ‘smart crack arrester’ concept to improve the damage tolerance of composite foam-core sandwich structures. The smart crack arrester can simultaneously arrest and detect a crack propagating along the interface between the facesheet and the core. Two fiber Bragg grating (FBG) sensors are embedded at both edges of the arrester to monitor the internal strain change induced by crack propagation. However, since the developed detection technique utilized transient elastic strain change during high-speed crack propagation, the system required a high-cost measurement system and could fail to detect a fatal interface crack in a practical noisy environment. Thus, this study advances the previous approach. Metal wires are additionally embedded alongside the FBG sensors, resulting in a more easily applicable and reliable crack-detection system with a new technical concept. Specifically, the characteristic strain state induced by arresting the interface crack is first ‘memorized’ by plastic deformation of the metal wire, and the consequent residual strain is then ‘statically’ picked up by the FBG sensor as a damage signal. This study begins by simulating deformation of the metal wires and the sensors to evaluate the feasibility of the proposed technique. The significant advantage of adding the metal wires is then demonstrated by comparing data from the new and previous approaches. Finally, a verification test is conducted to confirm that an FBG spectral shape statically obtained after unloading can indicate the propagation direction and tip location of an arrested crack.

Human intervertebral disc internal strain in compression: The effect of disc region, loading position, and degeneration

The primary function of the disc is mechanical; therefore, degenerative changes in disc mechanics and the interactions between the annulus fibrosus (AF) and nucleus pulposus (NP) in nondegenerate and degenerate discs are important to functional evaluation. The disc experiences complex loading conditions, including mechanical interactions between the pressurized NP and the surrounding fiber-reinforced AF. Our objective was to noninvasively evaluate the internal deformations of nondegenerate and degenerate human discs under axial compression with flexion, neutral, and extension positions using magnetic resonance imaging and image correlation. The side of applied bending (e.g., anterior AF in flexion) had higher tensile radial and compressive axial strains, and the opposite side of bending exhibited tensile axial strains even though the disc was loaded under axial compression. Degenerated discs exhibited higher compressive axial and tensile radial strains, which suggest that load distribution through the disc subcomponents are altered with degeneration, likely due to the depressurized NP placing more of the applied load directly on the AF. The posterior AF exhibited higher compressive axial and higher tensile radial strains than the other AF regions, and the strains were not correlated with degeneration, suggesting this region undergoes high strains throughout life, which may predispose it to failure and tears. In addition to understanding internal disc mechanics, this study provides important new data into the changes in internal strain with degeneration, data for validation of finite element models, and provides a technique and baseline data for evaluating surgical treatments.

Structural evolution in nano-crystalline Cu synthesized by high energy ball milling

Nano-crystalline copper with a mean crystallite size of 27 nm was synthesized through solid state reduction of Cu 2O by graphite using high energy planetary ball mill. The structural and morphological changes during mechanical milling were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mean crystallite size and residual strain were determined by XRD peak broadening using the Williamson–Hall approximation. It was found that the reaction is completed in a manner like a nucleation and growth process. Although the crystallite size and internal strain changes in Cu 2O were regular during mechanical milling, there was an irregularity in both parameters in Cu particles. This irregularity was probably due to the progressive formation of copper during milling.

A synchrotron radiation study of transient internal strain changes during the early stages of thermal cycling in an Al / SiC w MMC

The advent of x-ray synchrotron sources of extremely high intensity has opened up new opportunities for measuring internals strains deep within engineering materials. The authors report one of the first sets of engineering measurements made at the European Synchrotron Radiation facility (ESRF) achieving extremely fast measurement times ({much_lt}1 sec) and high strain resolution in transmission. This has enabled them to monitor the internal strains in 3 mm thick 10 vol% SiC{sub W}/Al metal matrix composite specimens undergoing thermal cycles of 6--12 minute duration. In this paper the authors focus on the development of elastic strain in both phases during the first few thermal cycles.

A new stroboscopic neutron diffraction method for monitoring materials subjected to cyclic loads: Thermal cycling of metal matrix composites

The use of Bragg diffraction techniques to determine the elastic strain state and thus the stress within a material has been established for several years. Neutrons have the advantage over the more widely used x-rays of greater penetration depth (e.g., half depth of {approximately}20mm in Al, c.f. {approximately}20 {micro}m for x-rays of comparable wavelength), allowing monitoring of bulk properties without the need for surface corrections or sectioning. However to date, long data acquisition times have hamstrung time resolved studies. In this paper the authors present a new stroboscopic method for the monitoring of rapid cyclic phenomenon and use it to study the internal strain changes occurring in an Al/10%SiC whisker composite during thermal cycling.

Modelling of time dependence in ultra-high-modulus polyethylene based on Raman microscopy

Previous research dealt with the modelling of time dependence in ultra-high-modulus polyethylene in terms of mechanical systems. Although such attempts were highly successful in describing time-related phenomena in melt-spun polyethylene, they were less able to account for the behaviour of gel-spun material. Moreover, in the early experiments, only the macroscopic deformation could be determined. Recent advances in Raman microscopy have enabled a study of the changes in internal strain associated with crrep and recovery. This short paper considers some preliminary creep data in terms of mechanical models which, despite their simplicity, are nevertheless able to provide a phenomenological basis for a number of the observed features: most notably the attainment of a strain maximum in one of the differently stressed structural components.

Bone dynamics: stress, strain and fracture.

Bone is a dynamic tissue whose functional mass is controlled by the balance between the endocrine drive towards bone resorption and the mechanically-engendered drive towards bone formation. Strain is the key intermediate variable between loading forces and bone remodelling. Animal studies have shown that static loading of bone has no osteogenic effect; bone loss occurs as if there were no loading at all. However, dynamic loading, that is, cyclic change in internal strain, is strongly osteogenic, with relatively few cycles required for maximum effect. However, if a sufficient number of cycles is applied, repetitive loading can cause stress fractures. This number decreases as internal strains increase. Thus strain redistribution within bone, as caused by muscle fatigue or improper sports equipment, is a significant cause of fracture.

Minimizing changes in internal strain in unimolecular nucleophilic displacement reactions

Minimizing changes in internal strain in unimolecular nucleophilic displacement reactions