Uniaxial Stress Field Research Articles

Modelling and validating of constitutive relationship between uniaxial stress and AC electromagnetic field

The phenomenon of stress-induced alteration in the magnetic field of ferromagnetic materials and certain conductive non-ferromagnetic materials is herein referred to as the mechano-electromagnetic effect (MEME). It has great application potential in nondestructive testing of stress. However, the physical mechanism of MEME is still unclear, and most stress-magnetic field correlation models are phenomenological and dependent on testing conditions, making them difficult to apply in measurements. In this paper, a constitutive model of MEME was established by assuming that the underlying physical mechanism of MEME is an intrinsic response of material to stress through changes in permeability and conductivity. Based on the constitutive models of stress–magnetic permeability and stress–conductivity, the uniaxial stress–AC electromagnetic-field constitutive model was proposed and validated. In the uniaxial tensile experiment of Q235 specimen, the prediction results of the model agree well with the experimental findings with satisfactory accuracy and generality. The constitutive model provides a new interpretation of the mechanism of MEME and a new method for simulation of stress-affected electromagnetic field.

The effects of stress ultrasonic rolling on the surface integrity and fatigue properties of TiB2/7050 Al composite

In the present work, a new surface mechanical strengthening (SMS) technique named stress ultrasonic rolling (SUR), which is ultrasonic rolling (UR) assisted with a uniaxial tensile elastic stress field, was reported and successfully conducted on 5 % wt TiB2/7050Al composite. Based on the experimental analysis and numerical simulation, the effects of SUR on surface integrity and fatigue performance of the composite were comprehensively investigated. Compared with ordinary UR, SUR further enhanced the fatigue strength at 106 cycles of the composite by 5 % and prolonged the fatigue life of the composite under the stress level of 532.8 MPa by 1.8 to 3.3 times, which are attributed to the comprehensive effect of excellent surface finish, larger and deeper compressive residual stress (RSc) layer, dispersed TiB2 particles distribution in the surface, and superficial nanocrystalline structures. Besides, the assistance of uniaxial tensile elastic stress field did not increase the amount of surface plastic deformation, which indicates the RSc generated by SUR should have similar mechanical and thermal stability to that produced by ordinary UR treatment.

Large reversible multicaloric effects over a broad refrigeration temperature range in Co and B co-doped Ni–Mn–Ti alloys

Solid-state refrigeration is considered a promising alternative to traditional vapor compression refrigeration technology. Researchers demonstrated that Ni–Mn–Ti alloys have a remarkable elastocaloric effect. However, the Ni–Mn–Ti alloy can only operate under a uniaxial stress field due to its antiferromagnetic austenite, which narrows its range of refrigeration temperatures. Here, we activated the magnetism of the alloy by replacing some Ni atoms with Co atoms. The Ni–Co–Mn–Ti–B alloy demonstrates a reversible maximum magnetic entropy change(ΔSm) of 24.9 J kg−1 K−1 and achieves an adiabatic temperature change of 7.8 K under a 7 T magnetic field. Additionally, we demonstrate that adding boron (0.2%) can improve the mechanical properties and cyclic stability in Ni–Mn–Ti alloys. The elastocaloric effect of 21.3 K with high cycle stability (1013 cycles) were successfully achieved in the directionally solidified (Ni35Co15Mn35Ti15)99.8B0.2 alloy. Furthermore, we have demonstrated that the magnetoelastic coupling effect can effectively extend the refrigeration temperature range. The alloys achieved large caloric effects in the temperature range of 240 K–340 K. This provides a new strategy for designing high-performance materials for wide-temperature-domain refrigeration.

Electromechanical properties of [0 0 1]‐textured Mn–PMN–PZT ceramics under uniaxial pressure

AbstractDielectric, ferroelectric, and piezoelectric properties of both random and textured Mn–PMN–PZT ceramics were characterized under uniaxial stress. Textured ceramics exhibit a large piezoelectric response under uniaxial pressure; the bias field piezoelectric constant is higher than 700 pC/N when pressure is below 50 MPa. Moreover, textured ceramics also show better depolarization resistance under uniaxial stress fields; overall, 30% of the origin performance will remain when stress approaches 200 MPa, but for random ceramics, it is only 10%. The ferroelectricity of both random and textured ceramics is suppressed by uniaxial compression. Ec, Pr, Ei, and dissipation energy all decrease with increasing uniaxial stress. In addition, phase‐field simulation was used to better understand the polarization‐changing effects on piezoelectric and dielectric performance. The uniaxial stress causes polarization rotation and increases the angle between polarization and the electric field, which is an important factor leading to the increase of the dielectric constant.

Stress and electric field induced phase transitions for ultra high energy conversion in ferroelectrics

This work focuses on energy harvesting of ferroelectric relaxors PMN-25PT and PZN-8PT single crystals with high uniaxial stress and electric field. Ericsson cycle, which consists of applying and releasing electric field and stress at different steps of the cycle, has been used. A large energy density for PZN-8PT high as 410 mJ/cm3 was obtained. Different working temperatures were tested by experiment and modeled via Landau–Devonshire theory. Optimal working temperatures were identified for high level energy conversion and were successfully predicted by simulation. It appeared that the optimum working temperature was different from that optimizing the d33. Polarization mechanisms induced by these extreme conditions for energy harvesting are explained in the frame of experimental and modeling results. The results obtained at high stress levels tend to indicate that operating along the polarization direction yields the best results, which contradicts conclusions drawn in the case of domain engineered crystals.

Origin of quasi-linear superelasticity at high temperature in Ni–Mn-Ga-Co shape memory alloy

The quasi-linear superelasticity in Ni–Mn-Ga-Co shape memory alloy displays a complete recoverable strain of ∼3% at 473 K for the cubic phase in precursor state. The in-situ neutron diffraction experiments provide the direct evidence on the stress-induced transition from the precursor state to martensite via the continuous variation of lattice parameter and peak width under uniaxial stress field. The anomalous broadening in peak width suggests that the external stress field may trigger very high heterogeneity in lattice distortion for the initial precursor state having randomly-distributed domains with short-range strain ordering prior to the martensitic transformation. The origin of the quasi-linear superelasticity at high temperature is considered as the ruggedness of the local energy landscape. The present investigations provide new insight into the understanding of superelasticity in shape memory alloys.

Electromechanical properties of textured PIN-PSN-PT ceramics under uniaxial stress, hydrostatic pressure, and bias electric field

Textured relaxor-PbTiO3 ceramics have received considerable attention from both academia and industry, due to their crystal-like properties, high composition homogeneity easy-to-process, and relatively low cost compared to their crystal counterparts. In this work, the ⟨001⟩-oriented Pb(In1/2Nb1/2)O3-Pb(Sc1/2Nb1/2)O3-PbTiO3 textured ceramics were fabricated by the template grain growth method. To explore the property variation in these textured ceramics under practical applications of piezoelectric devices, their electromechanical properties were characterized and analyzed under uniaxial stress, hydrostatic pressure, and d.c. bias electric field. The results show that the dielectric constants of all textured ceramics increase with an increase in the uniaxial prestress and hydrostatic pressure but decrease with an increase in the d.c. bias electric field. Among all textured ceramics, the textured ceramic with 3 vol. % BT templates exhibits the best stability under external fields. In particular, the electromechanical coupling factors of the textured ceramic change less than 2% with the hydrostatic pressure increase to 100 MPa. This work provides important data on textured relaxor ferroelectric ceramics, which will benefit the design and application of piezoelectric devices based on textured piezoelectric ceramics.

Inverse identification of pipeline steel mechanical state by means of coupled magnetic measurements and artificial neural networks

Artificial neural networks are widely used to develop models able to predict properties of interest by learning and establishing relationships between inputs and outputs of a system. It is particularly relevant for the inversion process in the framework of Non-Destructive Testing (NDT) involving strongly non-linear and non-monotonic behavior and/or saturations. The case-study considered in this work is a magnetic material subjected to uniaxial mechanical stress, plastic strain and magnetic field. An Artificial Neural Networks (ANN) model is proposed to predict the corresponding remanent magnetization, coercive field and the maximum magnetization as target properties. A series of experimental data made of various magneto-mechanical measurements are used to train, evaluate and validate the ANN model. The proposed model suitably predicts the magnetic properties of a second specimen of the material in the same magnetic field, plastic strain and stress ranges as the first specimen. An inverse ANN is then proposed to evaluate the mechanical loading and the plastic strain from the magnetic signature. Unique and accurate solutions are found that proves the relevance of machine learning approach in such NDT application.

Spin-density-wave order controlled by uniaxial stress in CeAuSb2

The tetragonal heavy fermion compound CeAuSb$_2$ (space group $P4/nmm$) exhibits incommensurate spin density wave (SDW) order below $T_{N}\approx6.5~K$ with the propagation vector $\mathbf{q}_A = (\delta_A,\delta_A,1/2)$. The application uniaxial stress along the [010] direction induces a sudden change in the resistivity ratio $\rho_a/\rho_b$ at a compressive strain of $\epsilon \approx -0.5$\%. Here we use neutron scattering to show that the uniaxial stress induces a first-order transition to a SDW state with a different propagation vector $(0,\delta_B,1/2)$ with $\delta_B=0.25$. The magnetic structure of the new (B) phase consists of Ce layers with ordered moments alternating with layers with zero moment stacked along the $c$-axis. The ordered layers have an up-up-down-down configuration along the $b$-axis. This is an unusual situation in which the loss of spatial inversion is driven by itinerant magnetic order. We argue that the change in SDW wavevector leads to a concomitant Fermi surface reconstruction, similar to other materials where a SDW can be controlled by uniaxial stress or magnetic field such as Sr$_3$Ru$_2$O$_7$.

구멍 뚫기 방법을 이용한 균일한 응력장에서의 잔류응력 측정

Residual stress might not only cause structural failure in materials, but also have a significant influence on the safety and life of the object as it superposes with the load applied to machine components or structures. In this paper, the effect of the residual stress analysis procedure and relaxation coefficients was investigated for the practical application of the residual stress measurement method by hole-drilling method, and the reliability of this method was evaluated. To this end, a tensile test was performed to generate a known uniaxial stress field, and the relaxation strain was measured by drilling, and the residual stress was analyzed and compared. Under the conditions of the tensile test, the given longitudinal stress was 49.0 MPa and the transverse stress was 0, while the measured principal stresses were 40.0 MPa and -2.72 MPa. Considering that the general residual stress measurement method has an error of about 20-50%, it is shown that the residual stress measurement results obtained in this paper are reliable.

Multicaloric effect in synergic magnetostructural phase transformation Ni-Mn-Ga-In alloys

Multicaloric effect refers to a thermal response of materials driven by more than one external field. In this work, using a self-designed multicaloric effect characterization setup, we directly measured the adiabatic temperature change ($\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$) under uniaxial stress and magnetic field for a spin-lattice synergic coupled system of Ni-Mn-Ga-In. Both stress and magnetic field favor the martensitic transformation. A large $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$ of \ensuremath{-}6.7 K was achieved in the ${\mathrm{Ni}}_{57}{\mathrm{Mn}}_{18}{\mathrm{Ga}}_{21.45}{\mathrm{In}}_{3.55}$ alloy when simultaneously applying a moderate dual-external-field (uniaxial stress of 95 MPa and magnetic field of 2 T). Such a multicaloric $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$ is 72% higher than the single elastocaloric cooling, which is ascribed to the larger transformation volume fractions obtained under dual fields. Additionally, benefiting from the reduction in critical stress by a bias magnetic field, ${\mathrm{Ni}}_{57}{\mathrm{Mn}}_{18}{\mathrm{Ga}}_{21.45}{\mathrm{In}}_{3.55}$ exhibits a good fatigue resistance with a relatively stable $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$ of \ensuremath{-}5.7 K upon dual-field cycles of about 600 times. Our experimental results reveal that the multicaloric strategy based on the synergic magnetostructural transformation is feasible and promising for solid-state cooling under relatively lower driven fields.

Topology optimization of load-bearing capacity

The present work addresses the problem of maximizing a structure load-bearing capacity subject to given material strength properties and a material volume constraint. This problem can be viewed as an extension to limit analysis problems which consist in finding the maximum load capacity for a fixed geometry. We show that it is also closely linked to the problem of minimizing the total volume under the constraint of carrying a fixed loading. Formulating these topology optimization problems using a continuous field representing a fictitious material density yields convex optimization problems which can be solved efficiently using state-of-the-art solvers used for limit analysis problems. We further analyze these problems by discussing the choice of the material strength criterion, especially when considering materials with asymmetric tensile/compressive strengths. In particular, we advocate the use of a L1-Rankine criterion which tends to promote uniaxial stress fields as in truss-like structures. We show that the considered problem is equivalent to a constrained Michell truss problem. Finally, following the idea of the SIMP method, the obtained continuous topology is post-processed by an iterative procedure penalizing intermediate densities. Benchmark examples are first considered to illustrate the method overall efficiency while final examples focus more particularly on no-tension materials, illustrating how the method is able to reproduce known structural patterns of masonry-like structures. This paper is accompanied by a Python package based on the FEniCS finite-element software library.

Deviations in yield and ultimate tensile strength estimation with the Small Punch Test: Numerical analysis of pre-straining and Bauschinger effect influence

There is a growing interest on the Small Punch Test (SPT) and its many applications in a broad range of industries and sectors. The miniature volume of the SPT specimen eases the mechanical characterization of components and structures when standard tests are impracticable. But this miniature test is limited for one of its more constraining requirements: the material isotropy. Since this test subjects the material to triaxial stress and strain fields, isotropy is necessary to compare the resulted data from SPT with the standard tests, which generally show uniaxial stress fields. Another key element of this question is that initially, isotropic material can lose this property due to a cold pre-straining process and the existence of the Bauschinger effect. In this investigation, a numerical study with the finite element method was performed to understand the influence of pre-straining and the Bauschinger effect in yield strength and ultimate tensile strength estimation with the SPT. This study concludes that in the absence of isotropy, generated by a pre-straining, the SPT estimated a mean value of the principal yield strength components of the yield surface. It is also verified that presence of pre-straining in the SPT specimens invalidated their use to calculate the coefficients of the correlation equations for yield strength estimation.

Multicaloric effects in metamagnetic Heusler Ni-Mn-In under uniaxial stress and magnetic field

The world's growing hunger for artificial cold, on the one hand, and the ever more stringent climate targets, on the other, pose an enormous challenge to mankind. Novel, efficient, and environmentally friendly refrigeration technologies based on solid-state refrigerants can offer a way out of the problems arising from climate-damaging substances used in conventional vapor-compressors. Multicaloric materials stand out because of their large temperature changes, which can be induced by the application of different external stimuli such as a magnetic, electric, or a mechanical field. Despite the high potential for applications and the interesting physics of this group of materials, few studies focus on their investigation by direct methods. In this paper, we report on the advanced characterization of all relevant physical quantities that determine the multicaloric effect of a Ni-Mn-In Heusler compound. We have used a purpose-designed calorimeter to determine the isothermal entropy and adiabatic temperature changes resulting from the combined action of magnetic field and uniaxial stress on this metamagnetic shape-memory alloy. From these results, we can conclude that the multicaloric response of this alloy by appropriate changes of uniaxial stress and magnetic field largely outperforms the caloric response of the alloy when subjected to only a single stimulus. We anticipate that our findings can be applied to other multicaloric materials, thus inspiring the development of refrigeration devices based on the multicaloric effect.

Influence of the material anisotropy in the estimation of the yield strength with the Small Punch Test

The Small Punch Test (SPT) was developed in the 80’s as an alternative miniature test for the characterization of mechanical properties in the nuclear industry. One of the key aspects that materials must fulfill to be used with this miniature test is that of homogeneity and isotropy. The origin of the isotropy requirement comes from the fact that the estimation of mechanical properties using the SPT requires empirical correlations with standard tests, which generally show uniaxial stress fields. By contrast, the SPT shows a multiaxial stress field. There are few publications related with the influence of material anisotropy in the yield strength estimation using the SPT, and most of them are empirical studies. This research was intended to address, with a systematic finite element analysis, the influence that different anisotropy combinations could show in the yield strength estimation using the SPT. Thirty-six anisotropic hypothetical materials were evaluated with SPT simulations using the Hill’48 yield criterion. The yield strength of each material was estimated with the SPT using four correlation methods: Mao’s, CEN’s, the t/10 offset, and the optimized t/10. This study concluded that the SPT was not an appropriate test to evaluate or quantify the material anisotropy, but it was a valuable experimental test to estimate a mean yield strength of the six yielding stress components of the anisotropic material.

Preliminary Research on Response of GCr15 Bearing Steel under Cyclic Compression.

During the bearing service, a series of microstructural evolutions will arise inside the material, such as the appearance of feature microstructures. The essential reason for the microstructural evolution is the cumulative effect of cyclic stress. The Hertz Contact formula is usually adopted to calculate the internal stress, and there is a correlation between the shape and distribution of the feature microstructure and the stress distribution. But it is insufficient to explain the relationship between the morphology of feature microstructures and the rolling direction, such as specific angles in butterfly and white etching bands. The rolling phenomenon will cause the asymmetry of stress distribution in the material, which is the source of the rolling friction coefficient. Moreover, slipping or microslip will produce additional stress components, which also cause the asymmetry of the stress field. However, there is no experimental or theoretical explanation for the relationship between the asymmetry of the stress field and the feature microstructure. According to the current theory, the appearance of feature microstructures is caused by stress with or without rolling. Therefore, it is of great significance to study the formation mechanism: whether feature microstructures will appear in the uniaxial cyclic compression stress field without rolling. In this paper, uniaxial cyclic compressive stress was loaded into a plate-ball system and a cylinder system. The characteristics of microstructural change of bearing steel (GCr15) were studied. It was found that the hardness of the material increased after the cyclic compressive load, and the inclusions interacted with the matrix material. In the local microregion a white etching area was found, although the scale is very small. No large-scale feature microstructures appeared. Other phenomena in the experiment are also described and analyzed. For example, the production of oil film in the contact area and the changing law of alternating load.

Modeling of subsurface ceramic inclusions in metallic matrices

All engineering materials have the potential to contain inhomogeneities that can act as initiators for fatigue cracks during cyclic loading. One class of inhomogeneity that can occur as a result of the processes used to create metallic materials is a ceramic inclusion, typically resulting from the raw material contamination during the melting process. This article examines the predicted behavior of hard ceramic inclusions in a nickel-base superalloy metallic matrix. Compressive residual stresses are created in the inclusion during cool down from a stress-free state at high temperature. The influence of the proximity of the inclusion to the surface of the matrix material is examined, together with the impact of subsequent uniaxial loading on the stress field in the inclusion and in the surrounding material. The stress field in the ceramic inclusion is observed to transition from compressive to tensile as a function of the proximity of the inclusion to the surface of the material and the applied uniaxial stress field. For deep subsurface inclusions, the uniaxial stress field required to achieve a tensile stress in the inclusion is close to the yield stress of the material. The sensitivity of this critical stress to material cyclic hardening behavior and to the temperature difference between the stress-free state and the operating state is also explored. The significance of these modeling results is discussed in terms of the sensitivity of nickel-base superalloys to crack formation and growth from ceramic inclusions and hence the impact on probabilistic fatigue life assessments of the presence, location and size of the ceramic inclusions.

Mechanical Characterization of the Plastic Material GF-PA6 Manufactured Using FDM Technology for a Compression Uniaxial Stress Field via an Experimental and Numerical Analysis.

This manuscript presents an experimental and numerical analysis of the mechanical structural behavior of Nylstrong GF-PA6, a plastic material manufactured using FDM (fused deposition modeling) technology for a compression uniaxial stress field. Firstly, an experimental test using several test specimens fabricated in the Z and X-axis allows characterizing the elastic behavior of the reinforced GF-PA6 according to the ISO 604 standard for uniaxial compression stress environments in both Z and X manufacturing orientations. In a second stage, an experimental test analyzes the structural behavior of an industrial part manufactured under the same conditions as the test specimens. The experimental results for the test specimens manufactured in the Z and X-axis present differences in the stress-strain curve. Z-axis printed elements present a purely linear elastic behavior and lower structural integrity, while X-axis printed elements present a nonlinear elastic behavior typical of plastic and foam materials. In order to validate the experimental results, numerical analysis for an industrial part is carried out, defining the material GF-PA6 as elastic and isotropic with constant Young’s compression modulus according to ISO standard 604. Simulations and experimental tests show good accuracy, obtaining errors of 0.91% on the Z axis and 0.56% on the X-axis between virtual and physical models.

Magnetic frustration and spontaneous rotational symmetry breaking in PdCrO2

In the triangular layered magnet PdCrO2 the intralayer magnetic interactions are strong, however the lattice structure frustrates interlayer interactions. In spite of this, long-range, 120$^\circ$ antiferromagnetic order condenses at $T_N = 38$~K. We show here through neutron scattering measurements under in-plane uniaxial stress and in-plane magnetic field that this occurs through a spontaneous lifting of the three-fold rotational symmetry of the nonmagnetic lattice, which relieves the interlayer frustration. We also show through resistivity measurements that uniaxial stress can suppress thermal magnetic disorder within the antiferromagnetic phase.

A numerical and experimental study of the compression uniaxial properties of PLA manufactured with FDM technology based on product specifications

This paper presents a numerical and experimental study of the compression uniaxial properties of PLA material manufactured with FDM based on product specifications. A first experimental test in accordance with the requirements and conditions established in the ISO 604 standard characterizes the mechanical and elastic properties of PLA manufactured with FDM technology and product requirements in a uniaxial compression stress field by testing six specimens. A second experimental test allows analyzing the structural behavior of the industrial case, evaluating the compression stiffness, the compression yield stress, the field of displacements, and stress along its elastic area until reaching the compression yield stress and the ultimate yield stress data. To improve the structural analysis of the case study, a numerical validation was carried out using two analytical models. The first analytical model applies an interpolation procedure to the experimental results of the tested specimens in order to characterize the uniaxial tension-compression curve versus the nominal deformations by means of an 8-degree polynomial function. The second model defines the plastic material as elastic and isotropic with Young’s compression modulus constant and according to the guidelines established in ISO standard 604. The comparison between experimental tests and numerical simulation results for the study case verify that the new model that uses the proposed polynomial function is closer to the experimental solution with only an 0.36% error, in comparison with the model with Young’s compression modulus constant that reaches an error of 4.27%. The results of the structural analysis of the mechanical element indicate that the elastic region of the plastic material PLA manufactured with FDM can be modeled numerically as an isotropic material, using the elastic properties from the experimental results of the specimens tested according to ISO standard 604. In this way, it is possible to characterize the PLA FDM material as isotropic, obtaining as an advantage its easy definition in the numerical simulation software as it does not require the modification of the constitutive equations in the material database. SEM micrographs have indicated that the fracture of the failed test specimens is of the brittle type, mainly caused by the separation between the central plastic filament layers of the specimens. The results presented suggest that the use of FDM technology with PLA material is promising for the manufacture of low volume industrial components that are subject to compression efforts or for the manufacture of components by the user.