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The purpose of this research is to understand the effect of process parameters in multi-pass, mandrel-free, room-temperature tube-spinning, and in particular the role of axial feed-rate on the shape and thickness change when producing a hemisphere. This is tackled with a combination of experiments and analysis. The material of this study is heat-treated, commercially-pure aluminum (AA1070) tubes of 100 mm diameter. To produce the hemisphere, seven linear passes are selected. The spinning experiments are conducted for two tube thicknesses (2 mm and 3 mm) under three different axial feed-rates (2, 5, and 7.5 mm/rev.) and identical radial feed-rate (5 mm/pass). It is found that decreasing the axial feed-rate generates less spatial variation in the final thickness, while also making the process slower. During every experiment, the tube wrinkles axially. The experiments are interrupted after different spinning passes, and the shape and thickness are measured. Three different finite element models are described, using axisymmetric, shell and solid elements, respectively. Comparing them to the experiments shows that the computationally-efficient axisymmetric model gives reasonable shape and thickness predictions. The shell element model tends to overpredict the shape and thickness evolution during spinning, while being about 250 times slower. Finally, the solid element model provides good agreement with the experiments across the board, while being only 2 times slower than the shell element one. Hence it is recommended for industrial practice to use the axisymmetric model for preliminary process design (i.e., selection of toolpath and process parameters) and then to refine these selections with the solid element model.

Ionic devices consisted of ion-conductive ceramics such as solid oxide fuel cells (SOFC) and oxygen separation membranes have been developed in the last decades. La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), which is a mixed ionic-electronic conductive ceramics, is especially expected to play an important role in those ionic devices and so its electrochemical properties have been intensively studied.

The present study investigated thermo-mechanical behaviour of A-site deficient perovskites Li3xLa1/3-xTaO3 (LLTaO) and Li3xLa1/3-xNbO3 (LLNbO) with x = 0.00 to 0.06 as a function of temperature by means of thermo-mechanical analysis. LLTaO for all compositions exhibits an orthorhombic-tetragonal phase transition around 200 K, above which it has a tetragonal phase. As the temperature increases from 200 K to 400 K, the linear expansion coefficient shows a slight decrease for all the compositions, followed by a constant value of ~3 × 10−6 K−1 above 400 K regardless of x. On the other hand, LLNbO has an orthorhombic phase for x ≤ 0.02 and the tetragonal for x ≥ 0.04 at room temperature. The linear expansion coefficient of LLNbO with x ≤ 0.02 shows a peak around 470 K, which can be attributed to an orthorhombic-tetragonal phase transition. In addition, the expansion coefficient of LLNbO with x ≥ 0.02 significantly increases as the temperature rises from 200 K to 400 K, followed by a plateau and a relatively abrupt decrease after reaching a temperature above 600 K. Additional ionic conductivity measurement of LLNbO suggested that the inconstant expansion behaviour could be attributed to the lithium-ion motion.

In this study, a lanthanum cobaltite (LCO) “self-pulverisation” mechanism was investigated in an attempt use a novel concept when developing materials. The results confirmed that hydroxylation of a small amount of excessive La2O3 in LCO into La(OH)3 caused self-pulverisation of bulk LCO, which initially had a high mechanical strength, into very fine powders within a few weeks, from which cracks initiated and propagated. Other conventional oxides, such as stabilised zirconia. Intentionally added with the La2O3, were prepared and their self-pulverisation phenomena were demonstrated.

We have investigated the mechanical properties of porous La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) under uniaxial compression. Porous LSCF samples containing polymethyl methacrylate pore former with different diameters (0.4, 1.5 and 10 µm) were examined. The porosity increases with the increase in pore former content, and it also slightly increases with the increase in pore former size. The average pore size is constant for the same size pore former regardless of the porosity, and it is smaller than the original pore former diameter. X-ray diffraction confirms that all the samples have a rhombohedral crystal structure. The samples contain ferroelastic domains and exhibit clear mechanical behavior related to the ferroelasticity under uniaxial compression. The initial modulus, critical stress and compressive fracture strength of the porous sample decrease with the increase in porosity and pore size, where the dependence on the pore size is most clear for the fracture strength. An empirical equation to estimate the fracture strength of porous LSCF is proposed.

Oxidation kinetics and mechanical behaviours of Cr2AlC foam with a porosity of 53 vol.% were investigated. Microstructures of Cr2AlC foams oxidised in the temperature range 1173 to 1473 K for times between 0 and 100 h were examined. Uniaxial compression tests were performed at different temperatures in the range 298–1398 K to assess mechanical properties. The oxidation formed cohesive Al2O3 layers on the Cr2AlC matrix, beneath which porous Cr7C3 was formed. The oxidation kinetics can be expressed by a parabolic law. An excessive oxidation took place first in thin struts, where a breakage Al2O3 layer occurred, followed by an oxygen inflow and decomposition of inner material. At 298 K, non-oxidised Cr2AlC foam fracured intergranularly. Slight oxidation improved compressive strength, as the Al2O3 layer (2.5 µm or thinner) can prevent cracks to propagate from inside outward. However, an excessive oxidation deteriorated any improvement due to the breakage of Al2O3 layer in thin struts followed by the material decomposition. At 1273 K and 1398 K, non-oxidised porous Cr2AlC fractured intergranularly, accompanied by a plastic deformation around small Al2O3 particles segregated at grain boundaries. Oxidised Cr2AlC foams with the Al2O3 thickness of 2.5 µm had a slightly higher brittle-to-plastic transition temperature (~1273 K) than dense Cr2AlC. A thicker Al2O3 layer (~5 µm) was required to reinforce the material due to inferior mechanical properties of Cr2AlC at high temperatures. On the basis of the elucidated oxidation and fracture mechanisms, a safety criterion for high-temperature applications was suggested.

The temperature-dependent work-hardening of AA6061-T6 aluminum alloy is investigated using a combined experimental-numerical approach. Uniaxial tension experiments are performed from room temperature to 500°C, and the force-displacement curves up to fracture are established. Both the yield strength and the work-hardening rate of the material decrease with increasing temperature. Despite the marked increase in the elongation-to-fracture, the uniform elongation remains limited, indicating the early appearance of diffuse necking in the elevated temperature tests. A simplified technique for identifying the work-hardening curves at elevated temperatures and beyond the limit of uniform deformation in uniaxial tension is proposed. The technique uses an isothermal, rate-dependent, finite element (FE) model of the experiments. The post-necking hardening curve is represented by a hybrid Swift/Voce hardening law combined with a form of Johnson-Cook strain-rate dependence. To identify the material model parameters at each temperature, an objective function that correlates the experimental and FE-predicted force-displacement curves is constructed and minimized. These model parameters are then fit with Fourier series across the temperature range considered here, providing smooth functions suitable for subsequent implementation in FE analyses of forming and structural problems. As an illustration, it is shown that a FE model utilizing these material parameters reproduces the full-field features of the elevated temperature experiments very well.

The present study investigated the possibility of evaluating ferroelastic mechanical characteristics by spherical indentation. Finite element simulation of spherical indentation, with a relatively large sphere, of a ferroelastic-plastic material was performed using characteristic bulk data of a typical ferroelastic oxide (La Sr Co Fe O). The simulation results showed that the ferroelastic mechanical behaviour cannot be observed in the indentation load vs depth curve, but is clearly observable in the indentation stress vs indentation strain curve, which can be obtained reliably in experiments by estimating the contact radius using load-partial unloading sequences. The method can be reliable when the indentation stress is under the upper ferroelastic critical stress. Therefore, in principle ferroelastic mechanical characteristics could be evaluated by spherical indentation by obtaining the indentation stress vs indentation strain curve using partial unloading to estimate the contact radius, although the requirements are very difficult to satisfy in actual experiments.

The present study proposes a method to predict the burst pressures (BPs) of type III filament winding carbon fiber-reinforced plastic (CFRP) composite pressure vessels considering the inhomogeneity of carbon fiber packing through experimental work and simplified mechanical models reflecting the evolution of local damage in the CFRP layers. Vessels that had different carbon fiber volume fractions (Vfs) were prepared and tested to measure their BPs. The inhomogeneity of carbon fiber packing was evaluated using Weibull probability based on the microscopic observation of CFRP cross-sections in the virgin vessels. Detailed stress analyses of pressurized composite vessels considering the carbon Vf were conducted. Unstable fracture of the hoop layer was demonstrated by a simplified mechanical model combined with the inhomogeneity of the carbon Vf and de-bonding between the fiber and matrix. About 20% difference in the BP was measured between tested vessels with and without glass fiber-reinforced plastic layers over CFRP layers. The proposed method for predicting the BP based on the constant stress model enables consideration of the development of local fiber breaking prior to catastrophic fracture and to quantitatively estimate the change in the BP due to the difference in Vf.

The present work investigated the mechanical behavior of porous La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3− δ LSCF under uniaxial compression. The porous (LSCF) samples with the same grain size but different porous structures with 1.5–41% of porosity were prepared using three different pore formers. All the samples had ferroelastic domains and exhibited ferroelastic mechanical behaviors under uniaxial compression. Initial and loading moduli as well as critical stress monotonically decreased and remnant strain increased with increasing the porosity. The initial modulus can be determined by the actual porosity regardless of porous structure or grain size, whereas the other properties were more sensitive to experimental condition such as loading rate and maximum applied stress. Compressive fracture strength could be significantly influenced by porous structure.

This study investigates the mechanical behaviours of A-site deficient perovskite-type Li3xLa1/3−xNbO3 electrolytes (3x = 0.00–0.18) with domain structures. The samples were examined under uniaxial compression in the temperature range of 233–393 K. In the stress vs. strain relationship, the orthorhombic Li3xLa1/3−xNbO3 (3x ≤ 0.06) clearly exhibits non-linear elastic hysteresis, whilst the tetragonal one (3x ≥ 0.12) shows a simple elastic behaviour. Ex-situ scanning electron microscopy observation on a polished surface before and after compression confirmed the martensitic reorientation of the domain structure of the orthorhombic Li3xLa1/3−xNbO3, which explains the observed non-linear hysteresis, whereas the domains of the tetragonal sample remain almost unchanged.

The present molecular dynamics study investigated lithium-ion diffusion in La2/3–xLi3xTiO3 (x = 0.115) with various structural configurations. The diffusion path and conductivity vary significantly depending on the configuration despite the constant lithium content. A highly-ordered configuration in the in-plane or out-of-plane directions tends to require higher activation energy for diffusion. In each configuration, the largest bottleneck area is found in the principal migration path with the short of Ti–Ti distance along the path. A comparison between various models revealed that the activation energy depends not on the size of the bottleneck area but on the dimensionality of lithium motion: a higher dimensionality such as three-dimensional diffusion lowers the activation energy.

In this study, the oxygen non-stoichiometry in La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) under uniaxial compressive stress up to 77 MPa was investigated by means of coulometric titration. The oxygen deficiency determined by the transient current was almost constant under compression, whereas both cell resistance and relaxation time significantly increased and these two parameters showed good correlation. Their increase appears to be related to the oxidation process on the surface of LSCF decelerated by the contact pressure, whereas the compressive stress had little effect on the oxygen deficiency in LSCF. Creep deformation was found to have limited effect on oxygen deficiency. Experimental observation also demonstrated that chemical expansion could cause unexpected internal stress, which would not change the oxygen deficiency.

The present study investigates the mechanical deformation response of lanthanum aluminate (LaAlO 3 ) under various loading rates and temperatures. Ferroelastic domains were observed in samples of different porosity. Uniaxial compression tests were performed at room temperature and different loading rates ranging from 0.03 to 5.75 MPa/s. Temperature variation experiments were performed at 93 K, 193 K, 293 K, 393 K, and 553 K. LaAlO 3 shows non-elastic stress-strain behavior in which hysteresis loops are observed during loading–unloading cycles owing to ferroelasticity. The slope of the stress-strain curve became steeper with increasing loading rate and temperature. After unloading, remnant strain was stored in the material owing to ferroelastic domain switching.

The mechanical behaviours of lanthanum metal oxides LaCoO3 (LCO), LaAlO3 (LAO), LaGaO3 (LGO), and LaFeO3 (LFO) were investigated under uniaxial compression. Ferroelastic domain structures were observed as striped patterns in LCO, LAO, and LGO, but not in LFO. Rhombohedral LCO displayed a higher critical stress and larger hysteresis in its stress–strain curve than rhombohedral LAO, which could be attributed to the larger rhombohedral angle of LCO than that of LAO. Orthorhombic LFO-B (sintered at 1673 K) exhibited a larger hysteresis and stronger back-switching behaviour than orthorhombic LGO possibly because of the larger orthorhombic strain of LFO-B, whereas LFO-R (sintered at 1473 K) showed elastic behaviour. Comparison revealed that the rhombohedral ferroelastic materials exhibit smaller stress range for domain switching, resulting in more distinct ferroelastic mechanical behaviour, than the orthorhombic ones. This was confirmed by comparing the mechanical properties of LGO below and above its orthorhombic-to-rhombohedral phase transition temperature.

The creep behaviours of the dense and porous Cr2AlC ceramics were investigated, being the first study on creep behaviour of not only Cr2AlC but also porous MAX phase. Creep rates of rather dense (2% of porosity) and porous Cr2AlC (53% and 75%) were measured in the temperature range 1073–1473 K during heating and subsequent cooling after high temperature exposure. The compressive creep tests were performed under stress range of 1–12 MPa. Creep rates of porous Cr2AlC were higher than the ones of the rather dense material at lower temperature but lower at higher temperature, which can be attributed to effects of the formed oxide scale and some crack healing associated with the scale formation. A comparison of the creep rates with other refractory materials reveals favourable properties of the porous Cr2AlC.

The present study investigates the deformation behavior of lanthanum ferrite, LaFeO3 under uniaxial compression. Ferroelastic domains were observed in samples at high temperature etching which was confirmed by scanning electron microscopic observation. XRD patterns of all samples showed characteristics reflection with orthorhombic crystal structure. Uniaxial compression tests were carried out at temperature of 93K, 193K, 293K, 393K, and 553K, at a constant loading rate of 1.0 MPa/s. All samples exhibited non-elastic stress-strain behavior during loading- unloading cycles owing to ferroelasticity. The slope of the stress-strain curves increased with increasing the temperature as well as ferroelastic parameters, initial modulus and loading modulus were increased due to ferroelastic domain switching.

The present study investigates the mechanical behaviour of ferroelastic La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ with porosity ranging from 0.9% to 26.1% under uniaxial compression at room temperature. Both dense and porous samples have ferroelastic domains and exhibit ferroelastic mechanical behaviour. The apparent modulus, compressive strength and critical stress of the material dramatically decrease with increasing porosity, exhibiting exponential relationships. Comparison of the mechanical behaviours of samples with similar porosity but different porous structures reveals that the ferroelastic mechanical behaviour depends not only on porosity but also structural factors such as pore size and distribution.

The current study investigates Sr surface segregation phenomenon for polycrystalline La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 − δ annealed under four-point bending stress to elucidate effects of tensile and compressive stress on the segregation at elevated temperature (1173 K). On the stress-free surface, Sr segregation was mostly observed at the grain boundaries, whereas, on the tensile surface, finer and fewer segregation particles appeared at grain boundaries. For compressive surfaces, the segregation of much smaller and fewer particles was observed at the grain boundaries but also within the grain interiors. The surface segregation was assigned to a Sr-rich phase, possibly SrSO 4 . The present results indicate that Sr surface segregation could be suppressed by applying mechanical stress, especially compressive stress, which could be explained by a counteraction between Sr migration for surface segregation and creep deformation.

Apparent Young’s, shear and bulk moduli and Poisson’s ratio of freeze-cast La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF), envisaged as porous substrate for dense LSCF oxygen transport layers, were investigated at room temperature by a quasi–static hysteresis compression test as a function of the longitudinal strain which was measured in longitudinal direction. Ferroelastic domains were confirmed via electron microscopy. The apparent elastic parameters showed extrema related to ferroelastic domain switching. Apparent Young’s and shear moduli revealed minimum values, while bulk modulus and Poisson’s ratio demonstrated maximum values due to the transverse strain contributed by ferroelastic domain switching. Results are discussed with respect to the behavior and values of the elastic parameters that has been reported previously for dense LSCF.

The time-dependent deformation of porous (La0.6Sr0.4)0.95Co0.2Fe0.8O3-&delta, (LSCF) under constant uniaxial compressive stress at room temperature has been studied. Both axial and lateral stress&ndash, strain deformation curves clearly show the non-linear ferroelastic behavior of LSCF perovskite during compression. The ferroelastic characteristics of deformation curves such as coercive stress and apparent loading moduli decrease when the porosity of the samples increases. Ferroelastic creep deformations at applied stresses of 25 and 50 MPa demonstrate that stress and porosity are influencing factors on creep deformation, which increases with increasing stress and porosity. A negative creep or axial expansion and lateral contraction were observed in the sample with 35% porosity under 50-MPa constant compression stress.

In the present study, Sr surface segregation phenomena in La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) subjected to mechanical stress were investigated. LSCF specimens were mirror-polished and annealed under uniaxial compression or four-point bending. The polished surfaces before and after the annealing were characterized with a scanning electron microscope. In the uniaxial compression case, the number of the segregated particle is fewer but the particle size is larger for the compressed sample. In the case of four-point bending, a more significant segregation was observed on the tensile side than on the compressive side, whilst there is least segregation observed on the stress-free surface near the edges, which could be related to a stress gradient through thickness. The observation result indicates, therefore, that the surface segregation in LSCF could be controlled by applying mechanical stress.

The evolution of stress in the SiC particles during crack propagation under monotonic loading in a cast hybrid MMC was investigated by micro Raman spectroscopy. The experiment was carried out in situ in the Raman spectroscopy. Experimental results showed that cracks due to monotonic loading propagated by the debonding of the particle/matrix interface and particle fracture. Secondary cracks those formed in front of the main crack tip coalesced with the main crack in subsequent loading and final failure occurred. A high decrease in stress (several hundreds in MPa) was observed with the interfacial debonding at the interface and with the particle fracture on the particle. Moreover, the critical tensile stresses for particle–matrix interface debonding and particle fracture developed in hybrid MMC were also estimated during the crack propagation.

Uniaxial compression tests of ferroelastic La0.6Sr0.4Co0.2Fe0.8O3-δ were conducted in the temperature range covering the ferro-to-paramagnetic transition at ∼240 K (Tc). An anomalous variation of mechanical behaviour was observed. The apparent elastic modulus drastically decreases above Tc, whilst it is almost constant below Tc; on the other hand, the critical stress for ferroelastic domain switching decreases monotonically with increasing temperature. Furthermore, the back-switching occurs easily and/or rapidly below Tc, but the material becomes brittle.

The fatigue crack growth (FCG) mechanism of a cast hybrid metal matrix composite (MMC) reinforced with SiC particles and Al 2 O 3 whiskers was investigated. For comparison, the FCG mechanisms of a cast MMC with Al 2 O 3 whiskers and a cast Al alloy were also investigated. The results show that the FCG mechanism is observed in the near-threshold and stable-crack-growth regions. The hybrid MMC shows a higher threshold stress intensity factor range, Δ K th , than the MMC with Al 2 O 3 and Al alloy, indicating better resistance to crack growth in a lower stress intensity factor range, Δ K . In the near-threshold region with decreasing Δ K , the two composite materials exhibit similar FCG mechanism that is dominated by debonding of the reinforcement–matrix interface, and followed by void nucleation and coalescence in the Al matrix. At higher Δ K in the stable- or mid-crack-growth region, in addition to the debonding of the particle–matrix and whisker–matrix interface caused by cycle-by-cycle crack growth at the interface, the FCG is affected predominantly by striation formation in the Al matrix. Moreover, void nucleation and coalescence in the Al matrix and transgranular fracture of SiC particles and Al 2 O 3 whiskers at high Δ K are also observed as the local unstable fracture mechanisms. However, the FCG of the monolithic Al alloy is dominated by void nucleation and coalescence at lower Δ K , whereas the FCG at higher Δ K is controlled mainly by striation formation in the Al grains, and followed by void nucleation and coalescence in the Si clusters.