Initial Compressive Stress Research Articles

Phase Field Damage Framework for Modeling Thin-Film Silicon Anodes in All-Solid-State Batteries

Recent advancements in solid electrolyte research have revived interest in the concept of silicon anodes for All-Solid-State Batteries (aSSBs). Tan et al. have recently proposed stable cyclic performance of micro-grain size pure silicon anodes paired with sulfide-based solid electrolytes [1]. This development has opened pathways toward potential aSSBs without encountering dendrite growth issues. This rediscovery of the thin-film a-silicon anodes concept has sparked computational interest in simulating the fracture-chemo-mechanical silicon lithiation mechanism. Understanding chemical reactions during lithiation and crack evolution during de-lithiation processes are intriguing topics. Especially, elastic-plastic deformation coupled with phase-field continuous fracture is crucial in comprehending the underlying physics and enhancing performance of battery cell through reverse engineering approaches.In this work, we develop a thermodynamically consistent deformation-diffusion-damage coupled framework to model the evolution of dense, thin-film-like a-silicon anodes during lithiation and delithiation. During delithiation, tensile stress develops inside the film as the lithiated film overcomes the initial stack pressure and compressive stress prevalent during lithiation. As tensile stress and strain evolve, randomly distributed weak spots lead to crack nucleation. This fracture occurs throughout the silicon film, forming sharp vertical cracks, and depending on surface conditions along the solid-state electrolyte, some interfacial cracks may emerge, leading to permanent contact loss and resulting in capacity reduction.From the model, we observed “mud crack” like phenomena, where crack distribution is not controlled by particle’s property, but entire cluster’s thickness matters. While flat model suggests that one that nucleate the crack was weak spots where they make stress concentration over entire body, whether they can evolve into big vertical crack mostly governed by connectivity of such weak spot maps. However, from our interface roughness model, what governs the crack evolution most was not the randomly distributed weak spot, but its geometric relative thickness difference between one another. Due to manufacturing process, perfect interface is hard to be achieved and such geometric irregularity always exist, thus, additive and binder studies along the silicon anode and its interface between sse would be key to achieve long and stable life span for a-silicon based aSSBs. Reference [1] Tan, Darren HS, et al. "Carbon-free high-loading silicon anodes enabled by sulfide solid electrolytes." Science 373.6562 (2021): 1494-1499.

Influence of confining pressure on rock fracture propagation under particle impact

Revealing the influence of confining pressure on the propagation and formation mechanism of rock cracks under particle impact is significant to deep rock excavation. In this study, the three-dimensional fracture reconstruction of the rock after particle impact was carried out by CT scanning, and the stress and crack field evolution of the rock under particle impact were analyzed by PFC2D discrete element numerical simulation. The results demonstrate that after particles impact, a fracture zone and intergranular main crack propagation zone are formed in the rock. The shear stress and tensile stress caused by compressive stress are the main reasons for the formation of the fracture zone, while the formation of the intergranular main crack propagation zone is mainly due to tangential derived tensile stress. The confining pressure induces prestress between rock particles such that the derived tensile stress needs to overcome the initial compressive stress between the particles to form tensile fractures. And the increase in the confining pressure leads to increases in the proportion of shear cracks and friction effects between rock particles, resulting in an increase in energy consumption for the same number of cracks. From a macroscopic perspective, the confining pressure can effectively inhibit the generation of cracks.

Micromechanical analyses on bending of polysynthetically twinned single crystal of titanium aluminide

Micromechanical bending analyses via CPFEM of polysynthetically twinned (PST) single crystal of TiAl composing of one α2-phase lamella and six γ–phase lamellae have been performed. The results have demonstrated that a decrease in the domain size aspect ratio λD/λL or an increase in the volume fraction of α2 phase fα2 have an effect of increasing the induced bending moment and consequently bending resistance under both bending modes of hogging and sagging. The similar variations in λD/λL and fα2 results in a decreasing trends of maximum tensile and compressive initial yield stresses (normal bending stresses), obtained through small strain beam theory. Results have also shown the effects of imposed constraints on the bending behavior; traction-free boundary conditions result in activation of prismatic slips instead of pyramidal slips in α2-phase, leading to a lower observed bending moment for the variables λD/λL and fα2 considered. A scaling law is proposed that relates bending moment to domain size aspect ratio and bending angle.

Effect of mechanical stress on the traps in silicon nitride thin films

Silicon nitride (SiNx) films were prepared by plasma enhanced chemical vapor deposition (PECVD) and different traps were induced in the films by tuning the RF power ratio during film deposition. Different initial stresses were applied to study the relationship between the mechanical stress and trap density. In-situ stress measurements showed that the film densification occurred above 400 °C during the first thermal cycling. The trap density extracted by the capacitance-voltage measurements showed its lowest value (−0.10 × 1011 cm−2eV−1) at the initial compressive stress (−730 MPa) of the film, which was explained by the hydrogen elimination due to the ion bombardment during the deposition in the compressive film. The increase in trap density (1.60 × 1011 cm−2eV−1) for the tensile films (480 MPa) is attributed to the lowering of the ion bombardment, which increases the formation of Si-H bonds. Interestingly, the performed carrier lifetime measurements for the compressive stressed SiNx films are higher (1200 μs) than the tensile stressed SiNx films (750 μs) which validate the trap density calculations. Fourier transform infrared spectra and refractive index measurements showed that the Si/N ratio increased with the increasing initial stress. Overall, we predict that our current study facilitates the formation of highly endured nitride films for different electrical and optoelectronic applications.

Residual stress development and thermo-elasto-plastic distortion in brake discs

The relationship between thermo–elasto–plastic deformation during braking and the residual stress in brake discs is investigated experimentally in this study. X-ray diffraction is conducted to validate the residual stress distribution in the depth direction, whereas the cut/sectioning method is used to quantitatively measure the residual stress across a broader disc area. In addition, thermo–elastic distortion is quantified using thermal strain measured using a dynamometer. The compressive residual stress is distributed on both the circumferential and radial surfaces of unused brake discs with a magnitude of approximately 30 MPa, which transforms into a tensile stress exceeding 50 MPa in the circumferential direction after continuous braking tests, thus resulting in thermo–elastic distortion. This distortion is proportional to the tensile stress developed along the braking direction, which is primarily caused by plastic deformation due to external force and temperature gradient from the disc surface and core. The distortion magnitude ranges from 60 to 140 µm, depending on the type of pad material. Thermo–elastic disc distortion can be reduced by releasing tensile stress on the plastically deformed disc surface through abrasive wear using frictional pads. However, the magnitude of the initial compressive stress has minor effect on the distortion. The present experimental study provides insights into factors that affect thermo–elasto–plastic distortion in brake discs as well as methods that can reduce the distortion of brake discs in the design stage.

Strain rockburst failure characteristics and mechanism of high stress circular hard rock tunnel triggered by dynamic impact load

Strain rockburst poses a great threat to the construction safety of deep engineering, especially induced by dynamic impact loads such as blasting from the adjacent tunnel excavation. Aiming to clarify the failure characteristics and mechanism of strain rockburst induced by the dynamic impact load, a series of dynamic impact tests under different biaxial prestress conditions were conducted on the sandstone cube specimens with prefabricated circular holes by using the new biaxial Hopkinson pressure bar equipment. The real-time rockburst process and fracture characteristics on both sidewalls were captured by the high-speed camera. The test results show that the strain rockburst process can be divided into: the calm stage, slab buckling and spalling stage, rock slabs ejection stage, and V-shaped notch formation stage. Ultimately, a symmetrical V-shaped notch failure zone was formed on the sidewall, similar to the site. The strain field evolution characteristics and displacement deformation characteristics around the circular hole during the rockburst process were further explained by using digital image correlation (DIC). The failure mechanism of sidewall strain rockburst was closely related to spalling failure, characterized by dynamic tensile failure. The static stress provides the initial compressive stress field and governing the stress distribution around the tunnel. Dynamic impact load disrupts the original stress equilibrium of the surrounding rock, inducing significant alterations in internal stresses and strains within the surrounding rock, consequently inducing spalling or rockburst failure. The influences of lateral pressure on rockburst were also analyzed in detail, while the lateral pressure influences the severity of strain rockburst, which determines the dynamic load response characteristics, influence range of strain concentration zone, displacement deformation characteristics of the tunnel surrounding rock, and the severity of strain rockburst decreases with the increase of lateral pressure.

Comparative Studies of the Confined Effect of Shear Masonry Walls Made of Autoclaved Aerated Concrete Masonry Units.

Confined walls are popular in areas exposed to seismic action. The advantage of such structures is increased load-bearing capacity, ductility, and energy dissipation. Confined masonry walls are also used to restrain the intensity of cracking and improve load-bearing capacity in areas exposed to seismic action. This paper describes the research on 18 confined walls and presents a comparison with research on unconfined walls (referenced models). The confined models were classified into three series: HOS-C-AAC-without openings and with confining elements around the perimeter; HAS-C1-AAC with a centrally positioned opening and circumferential confinement; and HAS-C2-AAC with a centrally positioned window opening and additional confinement along the vertical edges of the opening. The area of the window opening was 1.5 m2. All walls were made of autoclaved aerated concrete (AAC) masonry units of the nominal density class of 600. The walls were tested under initial compressive stresses σc = 0.1; 0.75; and 1.0 N/mm2. The reference models without confinement (six models of the series HOS-AAC without openings and the series HAS-AAC with openings) were prepared from the same masonry units, had almost the same outer dimensions, and were tested under the same initial compressive stresses σc. The analysis was performed for the morphology of cracks, stress values at the moment of cracking and failure, stiffness, and angles of shear strain. The morphology of cracks was found to depend on initial compressive stresses and the presence of an opening. A significant increase in compressive stress leading to cracks and failure stresses was observed with increasing values of initial compressive stresses. As the wall behavior was clearly non-linear, the bilinear relationship described by energy dissipation E, stiffness at the moment of cracking Kcr, and maximum displacement uu was proposed to be included in the engineering description of the relationship between horizontal load and displacement of confined walls. Confinement along the vertical edges of the opening having an area of 1.5 m2 (acc. to EN 1996-1-1) increased the maximum forces Pmax by ca. 45% and marginally affected the ductility of the wall when compared to the elements with circumferential confinement.

Experimental Study of the Fatigue Life of Off-Highway Steel Wheels Using the Rim Section Test Approach

Wheels are structural components designed to sustain dynamic loads and avoid fatigue failures in service. For their validation, when standard fatigue tests are not feasible due to premature tyre wear, alternative methods should be used. In this paper, the rim section test approach is evaluated for the fatigue life assessment of steel rims for off-highway wheels. Customized specimens were studied by finite element analysis and subjected to bending fatigue tests to obtain the fatigue curve for the critical point of the rim. The results were also compared to fatigue data from standard tests of the base material, confirming the importance of testing components in conditions as similar as possible to the final ones in service. Additional measurements of the specimens’ surface hardness showed how this approach is valid to consider the effects of possible work hardening induced in the components by the production process. The residual stress state, instead, does not seem to be considered appropriately, since the initial compressive residual stresses of the component were released during the manufacturing of the specimens. The overall results of the study confirmed the suitability of the section test approach as an alternative method for the fatigue life evaluation of structural components. Moreover, it could be used for specific investigations concerning the influence of the production process parameters on wheel rims.

Analysis of Joints Patterns in Albian to Santonian Strata on the Eastern Flank of the Abakaliki Anticlinorium: Implications on Paleostress Conditions and Fluid Flow Properties in an Unconventional Petroleum System

An analysis of joint patterns were carried out on multiple exposures in Albian to Turonian strata belonging to the Abakaliki Formation (Asu River Group) and the Eze-Aku Formation (Eze-Aku Group) on the eastern flank of the Abakaliki Anticlinorium of the Southern Benue Trough. The analysis was carried out using FracPaQ a MATLAB based toolbox for quantification of fracture patterns. The tool was used to calculate fracture density, and intensity of the traces; to quantify scaling distributions, and to determine dilation tendencies, slip tendencies, and to quantify connectivity, and fluid flow directions. Analysis show the presence of two major joint systems: A Major Cross-Fold Joint (CF-J) system -orthogonal to the regional fold axes- consisting of the CF-J1 set trending NW/SE (315±5°), and a subordinate Longitudinal Joint System (L-J) -subparallel to the fold axes- consisting of a NE-SW L-j1 set, an ENE-WSW (60°±5°) L-j2 set, and an E-W trending L-j3 set. Fracture patterns show intensity and density ranging from 11.2395- 53.3443 m-1 and 85.2747- 629.5928 m-2 respectively. Joints in the NE-SW show high dilation and low slip tendencies given a NW-SE directed maximum principal horizontal stress σH stress field. The units of the Abakaliki Formation show better connectivity and lower permeability anisotropy as both fracture systems are well developed in those units. These joints, having formed in the period leading up to the Santonian inversion would have been ideal conduits for migration and flow of hydrocarbon and mineral fluids. The Cross-Fold System precedes the folding episode in the Santonian period and is likely a result of overpressure conditions due to disequilibrium compaction in the Albian- Turonian strata in an initial compressive regional tectonic stress field. The Longitudinal System formed later and is related to the outer-arc flexure of the folded units taking advantage of the nascent cleavage structures in the folded shale units.

Numerical Modeling and Analysis of Strengthened Steel–Concrete Composite Beams in Sagging and Hogging Moment Regions

Strengthening of composite beams is highly needed to upgrade the capacities of existing beams. The strengthening methods can be classified as active or passive techniques. Therefore, the main purpose of this study is to provide detailed FE simulations for strengthened and unstrengthened steel–concrete composite beams at the sagging and hogging moment regions with and without profiled steel sheeting. The developed models were verified against experimental results from the literature. The verified models were used to present comparisons between the effect of using external post-tensioning and CFRP laminates as strengthening techniques. Applying external post-tensioning at the sagging moment regions is more effective because of the exhibited larger eccentricity. In the form of an initial camber and compressive stresses in the bottom flange prior to loading, this reasonable eccentricity induces reverse loading on the reinforced beams, reducing the net tensile stress induced during loading. Using CFRP laminates on the concrete slab for continuous composite beams is more effective in enhancing the beam capacity in comparison with using the external post-tension. However, reductions in the beam ductility were obtained.

Transverse mixing zone under dispersion in porous media: Effects of medium heterogeneity and fluid rheology

The addition of an environmental remediation modifier—polymer solution—to a Newtonian fluid expands the distribution of remediation agents injected in situ into saturated aquifers (affecting plume velocity and deformation), enhancing remediation efficiency. However, the effect of the flow properties of the polymer solution on the macroscopic transverse dispersion remains poorly understood. In this work, a transparent thin-layer two-dimensional sandbox was constructed to simulate the aquifer, and the transverse distribution range of colored solute—permanganate solution and viscous shear-thinning fluid (permanganate solution + xanthan gum)—was captured in real-time by a camera device during transport in porous media. The boundary dispersion coefficient was obtained by fitting a breakthrough curve of the boundary concentration, while the overall plume dispersion coefficient was determined via image moment analysis. The effects of fluid rheology and heterogeneity on the transverse mixing of the plume were analyzed, and the mechanism of viscoelasticity-induced transverse dispersion and mixing enhancement was summarized. The results indicated that the anisotropic stress generated by polymer fluid deformation at high water velocity increased the fluctuation and transverse distribution of the plume, while higher-viscosity polymers increased the initial extrusion swelling and additional compressive stress, covering a larger area. Xanthan gum enhanced the transverse distribution of the plume mainly through initial injection-extrusion expansion effect, viscoelastic stability of the post-injection part, and streamline crossing attributed to elastic turbulence. This study also verified that the shear-thinning fluid enhanced the effect of transverse dispersion and mixing under heterogeneous conditions, providing insights applicable to groundwater remediation.

B4C–(Ti0.9Cr0.1)B2 composites with excellent specific hardness and enhanced toughness

AbstractDense and light B4C–(Ti0.9Cr0.1)B2 composites with excellent mechanical properties were designed and reactively densified from boron, TiC, and Cr3C2 powder mixtures by spark plasma sintering in this work. Due to solid solution effects, the as‐obtained B4C–(Ti0.9Cr0.1)B2 composite exhibited obviously enhanced hardness (43.2 ± 3.0 GPa at 9.8 N) and higher specific hardness (12.82 GPa cm3 g−1) together with improved flexural strength (663 ± 39 MPa) and fracture toughness (KIC, 5.40 ± 0.25 MPa m1/2), compared to the counterparts such as B4C–TiB2 composite and B4C. Toughening contributions in the as‐sintered ceramics were quantitatively analyzed, and higher KIC in B4C–(Ti0.9Cr0.1)B2 was mainly due to their larger initial fracture toughness and compressive stress toughening. The combination of these properties makes B4C–(Ti0.9Cr0.1)B2 composites exhibit great potentials in the application as lightweight structural materials. This work provided an inspiration to achieve lightweight materials with high performance through doping minor‐amount atoms into the matrix.

Residual stress stability of HFMI-treated transverse attachments under variable amplitude loading with the P(1/3) and the linear spectrum

The potential of HFMI treatment to increase fatigue life under service loading remains in debate. However, some recent studies show that even under variable amplitude loading (VAL), fatigue strength is increased compared to untreated welds. Discussions generally focus on the stability of initial compressive residual stresses, which may be reduced during VAL due to high peak stresses. In this context, the potential of HFMI treatment is often only attributed to residual stress stability. This study presents further results on the effect of VAL with a P(1/3) and a linear load spectrum on the residual stress stability of HFMI-treated transverse stiffeners (TS) made of mild steel (S355) and high-strength steel (S700M). The impact of random, High-Low and Low-High loading sequences on the fatigue strength as well as on the residual stress behaviour of HFMI-treated joints will be discussed.

Effect of mechanical load on resultant composite piezomodules

A mathematical model has been developed and, on its basis, analytical solutions have been found for the resulting "reduced" electroelastic characteristics, in particular, for deformation (shear) piezomodules and dielectric permeabilities of a transversal-isotropic piezoelectric material (composite), taking into account corrections due to the presence of mechanical axial stresses and electrodeformational reorientation of the axis of symmetry of the material properties under the action of an electric field. In the initial configuration, axial tensile and/or compressive stresses do not result in shear strains of the material, the shifts are initiated by the application of an electric field and are "amplified" by axial stresses of the initial configuration. The effect of increasing the resulting values of deformation piezomodules of the material from the action of axial stresses was revealed. The values of the applied axial stresses do not exceed the values of the loss of stability of the material (elements of the structure and, in general, the composite), which causes the preservation of the effect of increasing piezomodules also under the action of an alternating electric field. The results of numerical modeling are obtained for the transversal-isotropic polymer composite "silicone/PZT-4" with unidirectional piezoelectric fibers with a circular cross section as a partial (limit) case of the structure with oriented ellipsoidal inclusions using the known "generalized singular approximation" based on the method of Green functions of statistical mechanics of composites for calculating tensors of effective properties composite in the current configuration. Deformation anisotropy corrections are calculated through the current coordinates of the guide vector for the symmetry axis of the properties - the orientation direction of the fibers of the composite. It has been found that the most significant effect of increasing shear piezomodules is manifested for a unidirectional fibrous composite with a low-modulus polymer matrix "silicone/PZT-4" at small values of the volume fraction of rigid piezoelectric fibers from the action of compressive longitudinal axial stress.

The high-cycle fatigue behavior of carburized M50NiL steel with high-energy modification and compound infiltration: A comparative study

In this study, ultrasonic rolling (C + USRP) and plasma nitriding (C + N) is performed on the surface of M50NiL steel after carburizing， the tension-compression fatigue test of R = −1 on different samples. The results show that the maximum fatigue limit of C + N, C + USRP, and single carburizing are 770 MPa, 676 MPa, and 412 MPa, respectively. The residual stress relaxation in the fatigue process of C + N and C + USRP is tested and found that the initial residual compressive stress of C + N is lower than that of C + USRP, but its attenuation value is considerably smaller. The microscopic characterization of samples is conducted after the fatigue tests. The nanometer nitrogen compounds in the composite permeability layer showed a strong pinning effect, however, microplastic deformation limits the fatigue process. The C + N demonstrates a much lower residual compressive stress relaxation, consequently, the C + N short crack propagation effective driving force ΔKeff value decreases. As a result, due to the higher crack closure effect, the C + N fatigue limit is observed higher than the C + USRP.

Residual stress evolution and surface morphology in grinding of hardened steel following carburizing and quenching processes

AbstractIn this paper, the residual stress evolution and surface morphology of quenched 20Cr2Ni4A steel after surface grinding with alumina grinding wheel was investigated. The initial compressive residual stress in the surface layer evolved into tensile stress after grinding. Since thermal stress was the dominated factor, the effect of grinding speed and grinding depth showed significant effects on the level of residual stress. The tensile stress on the ground surface increased by more than 50 % when grinding speed increased from 26 m/s to 34 m/s at the feed speed of 0.19 m/s to 0.26 m/s. The increase of grinding depth from 0.02 mm to 0.03 mm resulted in the increase rate of tensile stress varying between 54 % and 85 % at specific feed speed and grinding speed. Due to the extrusion and cutting of abrasive particles, plastic deformation and grooves were found on the machined surface. The influence of grinding heat and grinding force caused a plastic deformation layer and grinding burn layer within 20 μm.

Stability of a plane Couette flow over inhomogeneously stressed solids

In this paper, we investigate the stability of a plane Couette flow over non-linear solids undergoing homogeneous or inhomogeneous initial stresses. Almost all biological and engineering structures are subjected to complex initial residual stresses. We probe here the stability characteristics of a plane Couette flow over these stressed solid surfaces. Since initial stress is commonly inhomogeneous in Nature, our main focus is to analyze the stability of flow over inhomogeneously stressed solids at all Reynolds number regimes, which was not investigated earlier. We apply an initially stressed neo-Hookean solid model which precludes the necessity of using the stress-free reference. A linear perturbation analysis based on an Eulerian–Lagrangian formulation determines the stability associated with short and finite wave modes for zero, low, and high Reynolds number flows. In presence of a uniform initial stress field, the short wave modes are stabilized by tensile stresses and destabilized by compressive stresses in the limit of creeping flow. A similar influence of pre-stress is observed in buckling of columns. On the other hand, the case of spatially varying initial stress is far more intricate due to the inhomogeneous shearing of the solid in the unperturbed state. A linear perturbation introduced to this complicated unperturbed state presents several interesting observations. We find multiple unstable modes for low Reynolds number (Re≪1) creeping flows which were not reported earlier to the best of our knowledge. While literature demonstrates only downstream unstable modes for a plane Couette flow, both upstream and downstream unstable modes are observed for inhomogeneously stressed solids in various Reynolds number regimes. In the creeping flow limit (Re=0), the stability depends mainly on the tensile or compressive initial stress at the solid–fluid interface. When this initial stress is compressive at the interface, only the finite wave modes determine the stability for all thicknesses instead of the short-wave modes. At higher Reynolds number, we report many more interesting results for spatially varying stress-fields which includes an unusual scaling of wall-mode validated through eigenmode analysis.

Using 2D integral breadth to study plastic relaxation in a quasi-lattice-matched HgCdTe/CdZnTe heterostructure.

Micro-Laue diffraction has been used to record cross-section profiles on a quasi-lattice-matched HgCdTe/CdZnTe heterostructure as a function of the stress induced by a flexion machine. The heterostructure may be decomposed into four different regions according to depth. Sufficiently far from the interface, the CdZnTe substrate is undisturbed by the HgCdTe layer, while the region situated 10 µm beneath the interface presents an in-plane lattice parameter adjustment to the +0.02% mismatched layer. The layer has a 2 µm critical thickness and, beyond, misfit dislocations induce a large peak broadening whose main direction changes with depth. The same occurs over the whole heterostructure once flexion-induced plastification has started. Consequently, the usual full width at half-maximum or integral breadth is no longer relevant, and only a newly defined and rotationally invariant 2D integral breadth correctly measures the plastification-induced peak broadening. Taking into account only the critical thickness region, a 15.1 ± 0.7 MPa tensile HgCdTe elastic limit was measured, slightly overestimated because of the initial compressive layer stress. It was observed that the plastic onset of the substrate perfectly matches the elastic limit of the layer, despite the fact that the substrate elastic limit is expected to be four times higher: a striking demonstration of the propagation of threading dislocations. The 'plastification easiness' is found to be 2.4 times smaller deep inside the substrate than in the layer critical thickness region, while in the substrate lattice adjustment region, the plastification easiness goes from the substrate to the layer value with a 22-25 MPa transition interval. This novel method using the 2D integral breadth allows for easy critical thickness measurement as well as precise plastic onset determination and plastification easiness assessment. It is a quite general method, since it may be applied to the vast class of epitaxial layers for which the critical thickness is larger than the micro-Laue beam size (currently 250 nm).

Stress evolution and thickness change of a lithium-ion pouch cell under various cycling conditions

To design large-sized lithium-ion battery modules for the application of electric vehicles and grid-level energy storage, it is of important significance to understand how stress and dimension of a single pouch cell fluctuate during charge/discharge cycles. In this study, stress evolution under the constant-thickness condition and thickness change under the constant-stress condition are measured for in-house fabricated pouch cells, respectively. The results of stress measurements show that the stress increase percentage generally decreases when the charge/discharge current increases, regardless of the value of the initial compressive stress. With the same current density, the stress increase percentage generally increases when the upper cutoff voltage increases. With the same current density and upper cutoff voltage, the stress increase percentage decreases when the initial compressive stress increases. The results of thickness measurements show that the volume expansion percentage generally increases when the current density increases, regardless of the value of the constant compressive stress. With the same current density, the volume expansion percentage generally increases when the upper cutoff voltage increases. With the same current density and upper cutoff voltage, the volume expansion decreases when the constant compressive stress increases. The results provide important insights into the design principles of battery packs.

Residual stress evolution of 8YSZ:Eu coating during thermal cycling studied by Eu3+ photoluminescence piezo-spectroscopy

Thermal barrier coatings (TBCs) are widely used to protect high temperature structure parts against oxidation and corrosion. The failure mechanism study of TBCs is very important and the stress evolution is core content of failure mechanism research. In this work, a 8YSZ:Eu coating was produced via atmospheric plasma spraying (APS) method. Thermal cycling tests was carried out at 1300 ℃. The residual stress evolution of the coating was detected by a Eu 3+ photoluminescence piezo-spectroscopy based on the relationship between stress and the peak position of 5 D 0 → 7 F 2 transition of Eu 3+ ions. The failure mechanism of the 8YSZ:Eu coating was also studied. The as-sprayed 8YSZ:Eu coating contains metastable t ´ -ZrO 2 and amorphous structure. The stress distribution is inhomogeneous with both compressive stress and tensile stress. After 1000 thermal cycles, the initial compressive stress changed to tensile stress due to the thermal expansion coefficients (TEC) mismatch and irreversible plastic deformation during thermal cycling. With thermal cycling going on, the compressive stress appeared again and the averaged tensile stress decreased due to the volume expansion caused by phase transformation of the t ´ -ZrO 2 to m-ZrO 2 and the formation of cracks. Formation of the thermally grown oxide (TGO), phase transformation, thermal expansion mismatch are factors for the coating failure. • A Eu 3+ photoluminescence piezo-spectroscopy was used to measure the residual stress. • The residual stress distribution and evolution of the 8YSZ:Eu layer during thermal cycling was studied. • A 8YSZ:Eu coating was prepared by atmospheric plasma spraying and thermal cycling behavior was studied.