Effects of mechanical deformation on electric performance of rechargeable batteries embedded in load carrying composite structures

Integrating rechargeable battery cells with fibre reinforced polymer matrix composites is a promising technology to enable composite structures to concurrently carry load and store electric energy, thus significantly reducing weight at the system level. To develop a design criterion for structural battery composites, rechargeable lithium polymer battery cells were embedded into carbon fibre/epoxy matrix composite laminates, which were then subjected to tensile, flexural and compressive loading. The electric charging/discharging properties were measured at varying levels of applied loads. The results showed that degradation in battery performance, such as voltagea and energy storage capacity, correlated well with the applied strain under three different loading conditions. Under compressive loading, battery cells, due to their multilayer construction, were unable to prevent buckling of composite face sheets due to the low lateral stiffness, leading to lower compressive strength that sandwich panels with foam core.

Effect of mean stress on multiaxial ratcheting life: a simplified life prediction model based on average equivalent stress amplitude

This article proposes a model to predict uniaxial and multiaxial ratcheting life by addressing the three primary parameters that influence failure life: fatigue damage, ratcheting damage and the multiaxial loading path. These three factors are addressed in the present model by (a) the stress amplitude for fatigue damage, (b) mean stress-dependent Goodman equation for ratcheting damage and (c) an inherent weight factor based on average equivalent stress to account for the multiaxial loading. The proposed model requires only two material constants which can be easily determined from uniaxial symmetric stress-controlled fatigue tests. Experimental ratcheting life data collected from the literature for 1025 and 42CrMo steel under multiaxial proportional and nonproportional constant amplitude loading ratcheting with triangular sinusoidal and trapezoidal waveform (i.e. linear, rhombic, circular, elliptical and square stress paths) have shown good agreement with the proposed model.

Three-dimensional Finite Element modelling of laser shock peening process

Laser shock peening (LSP) is an innovative surface treatment technique for metal alloys, with the great improvement of their fatigue, corrosion and wear resistance performance. Finite element method has been widely applied to simulate the LSP to provide the theoretically predictive assessment and optimally parametric design. In the current work, 3-D numerical modelling approaches, combining the explicit dynamic analysis, static equilibrium analysis algorithms and different plasticity models for the high strain rate exceeding 106s-1, are further developed. To verify the proposed methods, 3-D static and dynamic FEA of AA7075-T7351 rods subject to two-sided laser shock peening are performed using the FEA package–ABAQUS. The dynamic and residual stress fields, shock wave propagation and surface deformation of the treated metal from different material modelling approaches have a good agreement.

Fuzzy logic controller optimized by particle swarm optimization for DC motor speed control

In this paper, we presented an optimized fuzzy logic controller using particle swarm optimization for DC motor speed control. The controller model is simulated using MATLAB software and also experimentally tested on a laboratory DC motor. A comparison of the performance of different controllers such as PID controller, fuzzy logic controller and optimized fuzzy logic controller is presented as well. With reference to the results of digital simulations and experiment, the designed FLC-PSO speed controller obtains much better dynamic behavior compared to PID and the normal FLC designed. Moreover, it can acquire superior performance of the DC motor, and also perfect speed tracking with no overshoot. The optimized membership functions (MFs) are obviously proved to be able to provide a better performance and higher robustness in comparison with a regular fuzzy model, when the MFs were heuristically defined. Besides, experimental results verify the ability of proposed FLC under sudden change of the load torque which leads to speed variances.

Characterization on ferrite microstructure evolution during large strain warm torsion testing of plain low carbon steel

Ferrite grain/subgrain structures evolution during the extended dynamic softening of a plain low carbon steel was investigated throughout the large strain warm deformation by hot torsion. Microstructural analysis with electron back-scattering diffraction (EBSD) scanning electron microscope (FEG/SEM) was carried out on the ferrite microstructural parameters. The results showed that the warm flow stress–strain curves are similar to those affected only by dynamic softening and an extended warm flow softening is seen during large strain deformation up to 30. Furthermore, with an increase in strain up to ~ vert, similar1 the grain size of ferrite, misorientation angle and fraction of high-angle boundaries gradually decrease and fraction of low-angle boundaries increases. With a further increase in the strain beyond ~, vert, similar2, these parameters remain approximately unchanged. No evidence of discontinuous dynamic recrystallisation involving nucleation and growth of new grains was found within ferrite. Therefore, the dynamic softening mechanism observed during large strain ferritic deformation is explained by continuous dynamic recrystallization (CDRX).

Grain size effect on the warm deformation behaviour of a Ti-IF steel

The effect of grain size on the warm deformation behaviour of a titanium stabilized interstitial free (IF) steel was investigated using hot torsion. The initial work hardening regime is followed by the development of a broad stress peak after which work softening occurs. The hypothetical saturation stress (Estrin–Mecking model) and the stress at final strain were relatively insensitive to grain size. However, the strain to the peak stress was strongly dependent on the grain size at low values of the Zener–Hollomon parameter. A simple phenomenological approach, using a combined Estrin–Mecking model and an Avrami type equation, was used to model the flow curves. The hypothetical saturation stress, the stress at final strain and the strain to peak stress were modelled using three different hyperbolic sine laws. A comparison with independent data from the literature shows that the apparent activation energy of deformation determined in this work (Q=372 kJ/mol) can be used to rationalize the steady-state stress in compression data found in the literature.

Dynamic softening of ferrite during large strain warm deformation of a plain-carbon steel

The evolution of dynamic ferrite softening in a plain-carbon steel was investigated by torsion tests during warm deformation at 810 °C, in the two-phase (ferrite + austenite) region, and strain rate of 0.1 s−1 with different strains up to 50. The warm flow behaviour and ferrite microstructural parameters, such as grain size, misorientation angle across ferrite/ferrite boundaries, and the fraction of high-angle and low-angle grain/subgrain boundaries were quantified using electron back scatter diffraction. The results show that with increasing strain up to not, vert, similar2, the ferrite grain size and fraction of high-angle boundaries rapidly decrease and the fraction of low-angle boundaries increases. However, these parameters remain approximately unchanged with increasing strain from not, vert, similar2 to 50. The dynamic softening mechanism observed during large strain ferritic deformation is explained by dynamic recovery and continuous dynamic recrystallization.

Electron back scattered diffraction (EBSD) characterization of warm rolled and accumulative roll bonding (ARB) processed ferrite

An interstitial free (IF) steel was severely deformed using accumulative roll bonding (ARB) process and warm rolling. The maximum equivalent strains for ARB and warm rolling were 4.8 and 4.0, respectively. The microstructure and micro-texture were studied using optical microscopy and scanning electron microscopy equipped with electron back scattered diffraction (EBSD). The grain size and misorientation obtained by both methods are in the same range. The microstructure in the ARB samples after 6 cycles is homogeneous, although a grain size gradient is observed at the layers close to the surface. The through thickness texture gradient in the ARB samples is different from the warm rolled samples. While a shear texture (⟨110⟩//rolling plane normal direction (ND)) at the surface and rolling texture at the center region is developed in the ARB  samples, the overall texture is weak. The warm rolled samples display a sharp rolling texture through the thickness with increasing the sharpness toward the center. These differences are attributed to the fact that the central region of ARB strip is comprised of material that was once at the surface. The ARB process  can suppress the formation of shear bands which are conventional at warm rolled IF steels. EBSD study on the sample with 6th cycle of ARB following the annealing at 750 ◦C verified a texture gradient through the thickness of the sheet. The shear orientations at the surface and at the quarter thickness layers can be identified even after annealing. The overall weak texture and existence of shear orientations make ARB processed samples unfavorable for sheet metal forming in compare with warm rolled samples.

Deformation of magnesium alloys during laboratory scale in-situ x-ray diffraction

In this research work we developed a new laboratory based transmission X-ray diffraction technique to perform in-situ deformation studies on a far more regular basis that is not possible at large scale synchrotron and neutron facilities. We studied the deformation mechanisms in light weight magnesium alloys during in-situ tensile testing.

Microstructure evolution of martensitic Ti-6Al-4V alloy during warm deformation

The microstructure evolution of martensitic Ti-6Al-4V alloy was investigated through uniaxial hot compression at 700°C and a strain rate of 10-3 s-1. A combination of scanning electron microscopy observation in conjunction with high resolution electron back scattered diffraction (EBSD) was used to characterize the microstructure in detail. The development of the microstructure displayed continuous fragmentation of martensitic laths with increasing strain (i.e. continuous dynamic recrystallization), concurrently with decomposition of supersaturated martensite resulting in the formation of equiaxed grains. At a strain of 0.8, an ultrafine equiaxed grained structure with mostly high angle grain boundaries was successfully obtained. The current work proposes a novel approach to produce equiaxed ultrafine grains in a Ti-6Al-4V alloy through thermomechanical processing of a martensitic starting microstructure. © (2014) Trans Tech Publications, Switzerland.

Development of a laboratory-based transmission diffraction technique for in situ deformation studies of Mg alloys

A laboratory-based transmission X-ray diffraction technique was developed to measure elastic lattice strains parallel to the loading direction during in situ tensile deformation. High-quality transmission X-ray diffraction data were acquired in a time frame suitable for in situ loading experiments by application of a polycapillary X-ray optic with a conventional laboratory Cu X-ray source. Based on the measurement of two standard reference materials [lanthanum hexaboride (NIST SRM 660b) and silicon (NIST SRM 640c)], precise instrumental alignment and calibration of the transmission diffraction geometry were realized. These results were also confirmed by the equivalent data acquired using the standard Bragg-Brentano measurement geometry. An empirical Caglioti function was employed to describe the instrumental broadening, while an axis of rotation correction was used to measure and correct the specimen displacement from the centre of the goniometer axis. For precise Bragg peak position and hkil intensity information, a line profile fitting methodology was implemented, with Pawley refinement used to measure the sample reference lattice spacings (d o (hkil)). It is shown that the relatively large X-ray probe size available (7 × 714mm) provides a relatively straightforward approach for improving the grain statistics for the study of metal alloys, where grain sizes in excess of 114μm can become problematic for synchrotron-based measurements. This new laboratory-based capability was applied to study the lattice strain evolution during the elastic-plastic transition in extruded and rolled magnesium alloys. A strain resolution of 2 × 10-4 at relatively low 2θ angles (20-65° 2θ) was achieved for the in situ tensile deformation studies. In situ measurement of the elastic lattice strain accommodation with applied stress in the magnesium alloys indicated the activation of dislocation slip and twin deformation mechanisms. Furthermore, measurement of the relative change in the intensity of 0002 and 10 3 was used to quantify {10 2} 011 tensile twin onset and growth with applied load.

Warm deformation and annealing behaviour of iron-silicon-(carbon) steel sheets

Single pass warm rolling and compression experiments were carried out from ambient to 800°C for ultra-low carbon (ULC) steel with ∼100 ppm carbon and interstitial free (IF) steels, both with two levels of silicon. Subsequently, annealing was done in order to recrystallize the deformed specimens. The main purpose of this study was to understand the effects of rolling temperature and silicon on stress responses and textures. This study comprises two main themes: flow stress and strain rate sensitivity during compression and shear banding and textures in warm rolled specimens. The effects of deformation temperature on in-grain shear bands were different between ULC-Si and IF-Si steels. As in previous work with more conventional steels, in-grain shear bands in the IF grade had low sensitivity to rolling temperature, while those in the ULC grade depended significantly on the deformation temperature. However, the temperature profile of shear banding in the ULC grade was approximately 150°C higher than in previous work. Deformation and recrystallisation textures for both IF and ULC grades depended on their rolling temperatures. The variation of both grain size and texture after annealing can be explained by the rise and fall of in-grain shear banding activity which is related to the strain rate sensitivity.

Enhanced mechanical response of an ultrafine grained Ti-6Al-4V alloy produced through warm symmetric and asymmetric rolling

An equiaxed ultrafine-grained (UFG) microstructure was successfully produced in a Ti-6Al-4V alloy with an average grain size of 110-230. nm through symmetric and asymmetric warm rolling of a martensitic starting microstructure. The UFG material displayed a combination of ultrahigh strength and ductility at room temperature. Compared with the conventional symmetric rolling, the asymmetric rolling process led to a more pronounced effect of microstructure refinement and a higher tensile ductility. The optimum mechanical response was obtained though the asymmetric rolling at 70% reduction, offering an ultimate tensile strength of 1365. MPa and a total elongation of ~23%. Apart from the magnitude of grain refinement, the inclination of basal texture component from the normal towards the rolling direction during asymmetric rolling and possible strain induced β to martensite transformation may concurrently contribute to a remarkable tensile strength-ductility balance.