Local Strain Heterogeneities Research Articles

Local strain heterogeneity associated with Al/Si ordering in anorthite, CaAl2Si2O8, with implications for thermodynamic mixing behavior and trace element partitioning in plagioclase feldspars

Abstract Hard Mode IR powder absorption spectroscopy has been used to characterize local strain relaxation associated with Al/Si ordering in a suite of synthetic anorthite samples with structural states that vary from a high degree of Al/Si order through a metastable incommensurate structure at intermediate states of order to long-range order with I1 symmetry. The dominant feature accompanying the changing structural states is line broadening, which has been quantified by autocorrelation analysis and is attributed to local heterogeneous strain variations on a length scale of at least 1–5 unit cells. The autocorrelation results are consistent with contributions to the line broadening as being due to order parameters for both the C1 → I1 and I1 → P1 transitions, which couple biquadratically, λQod2Qdispl2. Close correlation with enthalpy variations from previously published calorimetric data indicates that the driving force for ordering can be understood in terms of elimination of strain fields arising from accommodating more or less rigid AlO4 and SiO4 tetrahedra in the feldspar framework. The metastable incommensurate structure of anorthite is closely analogous to the stable incommensurate structure that develops at intermediate compositions in the plagioclase solid solution, confirming that the same strain relaxation mechanism dominates the properties and behavior of all structural states across the solid solution. Elimination of strain heterogeneity by ordering on the basis of I1 symmetry determines the form of non-ideal mixing shown by the solid solution at high temperatures, and changes in elastic properties may contribute to a break in the slope of partitioning of trace elements between crystals and melt.

Local strain heterogeneity and damage mechanisms in zirconia particle-reinforced TRIP steel MMCs: in situ tensile testing with digital image processing

In this work, the microstructural deformation and damage mechanisms of TRIP steel metal matrix composites (MMCs) reinforced with Magnesia Partially Stabilized Zirconia (Mg-PSZ) particles are investigated by employing in situ tensile testing within a scanning electron microscope chamber, complemented by digital image correlation and advanced image processing techniques. The study is carried out on samples with varied volume fractions (0%, 10%, and 20%) of zirconia particles and damage mechanisms in different samples under specified loading conditions. Through both qualitative and quantitative assessments of deformation, damage, and clustering, the investigation provides a comprehensive understanding of the distribution and damage initiation. The study findings reveal that, generally, the steel matrix exhibits high toughness, with minimal occurrences of microcracking at high strains that cause significant damage. In samples with increasing particle content, delamination at the matrix–particle interface and cracking of Mg-PSZ particles were found to be critical contributors to material failure and were quantitatively analyzed using computational analyses conducted with MATLAB. The work highlights the initiation and evolution of each damage mechanism in zirconia particle-reinforced TRIP steel MMCs to facilitate scientists and engineers in improving manufacturing and application decisions in industries such as automotive, aerospace, and heavy machinery, which demand materials with exceptional toughness and durability.Graphical

On-chip very low strain rate rheology of amorphous olivine films

Recent observations made by the authors revealed the activation of stress induced amorphization and sliding at grain boundary in olivine [1], a mechanism which is expected to play a pivotal role in the viscosity drop at the lithosphere-asthenosphere boundary and the brittle-ductile transition in the lithospheric mantle. However, there is a lack of information in the literature regarding the intrinsic mechanical properties and the elementary deformation mechanisms of this material, especially at time scales relevant for geodynamics. In the present work, amorphous olivine films were obtained by pulsed laser deposition (PLD). The mechanical response including the rate dependent behavior are investigated using a tension-on-chip (TOC) method developed at UCLouvain allowing to perform creep/relaxation tests on thin films at extremely low strain rates. In the present work, strain rate down to 10−12 s−1 was reached which is unique. High strain rate sensitivity of 0.054 is observed together with the activation of relaxation at the very early stage of deformation. Furthermore, digital image correlation (DIC), used for the first time on films deformed by TOC, reveals local strain heterogeneities. The relationship between such heterogeneities, the high strain rate sensitivity and the effect of the electron beam in the scanning electron microscope is discussed and compared to the literature.

Shear yielding and crazing in dry and wet amorphous PLA at body temperature

Understanding the inelastic, rate-dependent mechanical response of biodegradable polymers is important for the design of load-bearing biodegradable structures with controlled deformation and failure response. In this study, we investigate the mechanical response of amorphous polylactic acid (PLA) in dry and wet conditions prior to the onset of degradation at body temperature. The presence of water decreases the glass transition temperature by 4.5 °C, the storage modulus by 21%, and the compressive and tensile yield strengths by about 10%, despite a small water uptake of 0.93 wt%. The tensile response of PLA is dominated by craze yielding, rather than shear plasticity, and is stable against necking despite pronounced strain softening and local strain heterogeneities measured by Digital Image Correlation (DIC). Further analysis of the DIC strain fields in dry and wet samples suggests a transition from pure craze yielding in dry samples to a coexistence of craze yielding and shear plasticity in wet samples. The mechanism shift between tension and compression behaviour of dry and wet PLA has implications for the design of load-bearing structures and for constitutive modelling.

4D local investigation of mechanical behavior of open-cell foams by enhanced morphological analysis and microstructure-adapted digital volume correlation for tribology applications

In ex-poro-hydrodynamic (XPHD) lubrication, fluid impregnated, open-cell elastomer foams constitute a composite material aiming to improve the load carrying and damping capacity of lubricated systems and to provide more environmentally sustainable solutions. The performance of XPHD-based devices depends on the interactions between solid and fluid phases, occurring and evolving simultaneously during dynamic compression of an imbibed foam. Even at normal regimes, the foam microstructure undergoes large deformations and is prone to strain concentrations which modify its local porosity and influence the mechanical behavior of the composite. In this context, this work focuses on the development of a systematic and accurate characterization technique for describing the main morphological changes happening under uniaxial compression of a high porosity dry open-cell polyurethane foam, by in-situ X-ray microtomography (μCT) testing. A combination of 3D image analysis and digital volume correlation (DVC) is considered to identify and trace the spatial and temporal location of key microstructural features at every loaded state. In this way, the detailed transformations of cells and pores obtained by this method are presented here to give further insight into the deformation mechanisms involved. Then, the advantages and the limits of the overall methodology in analyzing high porosity open-cell foams are regarded in terms of feature segmentation and measurement precision. Both a classic and a microstructure-adapted DVC are compared at their respective scales, and finally their sensibility to emphasize local strain heterogeneities is discussed.

Ultrahigh Energy Storage Density in Glassy Ferroelectric Thin Films under Low Electric Field.

The current approach to achieving superior energy storage density in dielectrics is to increase their breakdown strength, which often incurs heat generation and unexpected insulation failures, greatly deteriorating the stability and lifetime of devices. Here, a strategy is proposed for enhancing recoverable energy storage density(Wr ) while maintaining a high energy storage efficiency (η) in glassy ferroelectrics by creating super tetragonal (super-T) nanostructures around morphotropic phase boundary (MPB) rather than exploiting the intensely strong electric fields. Accordingly, a giant Wr of ≈86 J cm-3 concomitant with a high η of ≈81% is acquired under a moderate electric field (1.7 MV cm-1 ) in thin films having MPB composition, namely, 0.94(Bi, Na)TiO3 -0.06BaTiO3 (BNBT), where the local super-T polar clusters (tetragonality ≈1.25) are stabilized by interphase strain. To the knowledge of the authors, the Wr of the engineered BNBT thin films represents a new record among all the oxide perovskites under a similar strength of electric field to date. The phase field simulation results ascertain that the improved Wr is attributed to the local strain heterogeneity and the large spontaneous polarization primarily is originated from the super-T polar clusters. The findings in this work present a genuine opportunity to develop ultrahigh-energy-density thin-film capacitors for low-electric-field-driven nano/microelectronics.

Grain-scale strain heterogeneity as a function of crystallographic texture in phase-change electro-mechanical ceramics

A reduction in the orientation distribution of grains, via crystallographic texturing, is known to significantly enhance the electro-mechanical response in polycrystalline piezoelectrics. Through calculations of the electric-field-induced strain in phase-changing ceramics, the local strain heterogeneity was also found to increase with crystallographic texture. The increase in grain-scale strain heterogeneity potentially indicates greater stress concentrations within the polycrystal and may degrade the expected lifetime and fatigue behavior in these ceramics. In crystallographic symmetries with higher numbers of polarization directions, it was found that the magnitude of heterogeneity in the response was lower.

Comparison of Abdominal Aortic Aneurysm Sac and Neck Wall Motion with 4D Ultrasound Imaging

The rupture of abdominal aortic aneurysms (AAAs) is associated with high mortality despite surgical developments. The determination of aneurysm diameter allows for follow up of aneurysm growth but fails in precisely predicting aneurysm rupture. In this study, time resolved three dimensional ultrasound (4D ultrasound) based wall motion indices (WMIs) are investigated to see if they are capable of distinguishing between uneven affected regions of the aneurysm wall. In a prospective study, 56 patients with an AAA were examined using 4D ultrasound. Local longitudinal, circumferential, and shear strains were computed using custom methods. The deformation of the neck and sac of each aneurysm was characterised by statistical indices of the obtained distributions of local wall strains (WMIs): mean and peak strain, heterogeneity index, and local strain ratio. The locations of regions with highest local peak strain were determined. Compared with the aneurysm neck, the sac is characterised by low mean strain, but highly heterogeneous deformation, described by high local strain ratio and heterogeneity index. Differences were highly significant (p<.001) for all strain components. The regions with the highest circumferential peak strain were found more often in the posterior part of the aneurysm neck (p<.050) and sac (p<.001) regions, compared with other wall regions. No statistically significant correlation was found between the WMIs and maximum AAA diameter, except for longitudinal mean strain, which decreased with the increasing diameter (rho=-.42, p<.010). Characterisation of wall kinematics by 4D ultrasound based WMIs provides a new and independent criterion for the distinction of diseased tissue in the AAA sac and the less affected neck region. This is a promising step towards the establishment of new biomarkers to differentiate between the mechanical instability of the AAA and rupture risk.

Experimental approach for microscale mechanical characterization of polymeric structured materials obtained by additive manufacturing

In this paper, an original experimental method is developed for local strain characterization at the surface of additively manufactured polymeric materials. The process used herein is material extrusion. This experimental method is based on the use of microscopic speckle pattern deposited at the surface of micro single edge notched specimen (μ_SENT) made of acrylonitrile butadiene styrene (ABS). Two configurations of filament orientation were used for the specimen manufacturing. Images of the μ_SENT specimen surface were recorded during in-situ tensile test. The quantitative analysis of images was made by digital image correlation (DIC). The evolutions of the local strain heterogeneities and the crack tip are evidenced on the kinematic fields. It is shown that the crack propagates in the low resistance path which is the interface area between filaments. It is also evidenced that the intersection of perpendicular filaments in two adjacent layers blocks crack growth. The local strain evolutions at the surface of the specimen are compared to the macroscopic response of the material. The method developed herein allows the determination of the materials mechanical properties. The identification of the crack tip location using digital image correlation (DIC) and J-integral calculation lead to plot the J-R curve. The J-R curves comparison of the two specimen configurations shows that the fracture toughness is directly related to the material structure.

Surface patterning for combined digital image correlation and electron backscatter diffraction in-situ deformation experiments

A considerable amount of information can be gained from combined collection of both digital image correlation (DIC) measurements, and of electron backscattered diffraction (EBSD) data from the same area during in-situ deformation experiments. Such data collection remains a challenge, however, due the influence of the surface markers required for DIC on the EBSD data quality. In this work we demonstrate that by careful control of the sample preparation process, a two-step electropolishing method can be used to generate excellent surface markers for DIC where the markers are integral features on the surface. The method does not require any special equipment and can be used to collect high quality EBSD data and DIC data with sub-micron resolution on the same area during repeated loading as part of in-situ deformation experiments. Combined EBSD and DIC measurements are illustrated in this work for samples of Al deformed in tension to a strain of 10%. Due to the integral nature of the surface markers we demonstrate also that it is possible to perform DIC measurements up to large plastic strains, including the necked region within a tensile sample. A comparison of EBSD and DIC data collected from the same area of a tensile-deformed sample shows that although the EBSD data provide excellent information on the lattice rotations developed during deformation, these data cannot be directly used as a measure of local plastic strain on the scale of the deformation microstructure. The ability to collect both EBSD and DIC data during an in-situ experiment provides, therefore, an opportunity to explore further the complex relationship between local plastic strain heterogeneity and EBSD-based measures of crystal lattice rotation.

Preferred Orientation of Quartz in Metamorphic Rocks from the Bergell Alps

Crystal preferred orientation of 47 samples of quartzite and eight samples of associated marbles from the Bergell Alps have been analyzed with time-of-flight neutron diffraction and EBSD. The results show a clear distinction of texture types for quartzites transformed from Triassic sandstones and quartz layers in gneiss. Textures of Triassic quartzites are overall weak and display a maximum of c-axes perpendicular to the foliation or a crossed girdle perpendicular to the lineation. Pole figures for positive rhombs {10 1 ¯ 1} show a maximum perpendicular to the foliation and negative rhombs {01 1 ¯ 1} generally display a minimum. Based on polycrystal plasticity models this texture type can be attributed to a combination of basal and rhombohedral slip. Asymmetry of the distributions is attributed to simple shear and local strain heterogeneities. The relatively weak texture is partially caused by muscovite limiting dislocation motion and grain growth, as well as adjacent layers of marble that accommodate significant strain. Most quartz layers in gneiss, including mylonites, display a texture with a-axes parallel to the lineation and a c-axis maximum in the intermediate fabric direction. This texture type can be attributed to dominant prismatic slip. Many samples are recrystallized and recrystallization appears to strengthen the deformation texture. The study shows good agreement of neutron diffraction and EBSD. Neutron diffraction data average over larger volumes and maximum pole densities are generally lower and more representative for the bulk material. With EBSD the microstructure and mechanical twinning can be quantified.

Assessment of Stress-Strain Behavior of Corroded Steel Reinforcement Using Digital Image Correlation (DIC)

Abstract Understanding the stress-strain behavior of corroded rebars is essential for understanding the structural behavior of corroding reinforced concrete structures. However, conventional methods of testing have several drawbacks, which have led to differences in opinion among researchers regarding the mechanical behavior of corroded rebars. This article proposes an improved method using Digital Image Correlation (DIC) to assess the stress-strain behavior of corroded rebars. The study is conducted in two phases: (a) development of the testing and evaluation method and (b) determination of the mechanical properties (i.e., yield strength, ultimate strength, and ultimate strain) of naturally corroded cold-twisted deformed (CTD) steel rebars using the developed method. The stress-strain behavior of one pristine plain mild (PM) steel and 13 naturally corroded steel rebars collected from a 15-year-old building are investigated in this study. The experimental results show that the proposed method can provide more accurate estimates of mechanical properties than the conventional methods. The developed method facilitates a better understanding of the stress-strain behavior at the fracture location (FL) and other local points of interest on corroded steel rebars. Because DIC measures local strains, the proposed method is able to measure local strain heterogeneity and therefore distinguish between the effects of geometrical variations from those due to true material degradation. This is in contrast to the conventional methods wherein deformation is measured over a finite gauge length, which results in a measurement of average deformation rather than true local deformation. This study emphasizes the need for measurement of full-field deformation to assess the stress-strain behavior of the corroded rebars with highly uneven cross-sectional area.

Effect of Strain Heterogeneities on Microstructure, Texture, Hardness, and H-Activation of High-Pressure Torsion Mg Consolidated from Different Powders.

Severe plastic deformation techniques, such as high-pressure torsion (HPT), have been increasingly applied on powder materials to consolidate bulk nanostructured materials. In this context, the aim of the present study is to compare the plastic deformation characteristics during HPT of two distinct Mg-based powder precursors: (i) atomized micro-sized powder and (ii) condensed and passivated nanopowder. Dynamic recrystallization could take place during HPT consolidation of the atomized powder particles while the oxide pinning of the grain boundaries restricted it for the condensed powder. Consequently, there have been substantial differences in the development of the microstructure, texture, local strain heterogeneities, and hardness in the two types of consolidated products. Different types of local strain heterogeneities were also revealed in the consolidated products. The associated diversity in microstructure within the same consolidated product has been demonstrated to have an effect on the hydrogen activation kinetics to form hydrides for these Mg-based materials that could be suitable for solid state H-storage applications.

Publisher's Note: Influence of local strain heterogeneity on high piezoelectricity in 0.5Ba(Zr0.2Ti0.8)O3−0.5(Ba0.7Ca0.3)TiO3 ceramics [Phys. Rev. B 95 , 054116 (2017)

Publisher's Note: Influence of local strain heterogeneity on high piezoelectricity in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>0.5</mml:mn><mml:mi>Ba</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mi>Zr</mml:mi><mml:mrow><mml:mn>0.2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi>Ti</mml:mi><mml:mrow><mml:mn>0.8</mml:mn></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>−</mml:mo><mml:mn>0.5</mml:mn><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mi>Ba</mml:mi><mml:mrow><mml:mn>0.7</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi>Ca</mml:mi><mml:mrow><mml:mn>0.3</mml:mn></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:msub><mml:mi>TiO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math> ceramics [Phys. Rev. B <b>95</b> , 054116 (2017)

Local strain heterogeneity and elastic relaxation dynamics associated with relaxor behavior in the single-crystal perovskite Pb(In1/2Nb1/2)O3−PbZrO3−Pb(Mg1/3Nb2/3)O3−PbTiO3

Recently, $\mathrm{Pb}(\mathrm{I}{\mathrm{n}}_{1/2}\mathrm{N}{\mathrm{b}}_{1/2}){\mathrm{O}}_{3}\text{\ensuremath{-}}\mathrm{PbZr}{\mathrm{O}}_{3}\text{\ensuremath{-}}\mathrm{Pb}(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}){\mathrm{O}}_{3}\text{\ensuremath{-}}\mathrm{PbTi}{\mathrm{O}}_{3}$ (PIN-PZ-PMN-PT) relaxor single crystals were demonstrated to possess improved temperature-insensitive properties, which would be desirable for high-power device applications. The relaxor character associated with the development of local random fields (RFs) and a high rhombohedral-tetragonal (R-T) ferroelectric transition temperature $({T}_{\mathrm{R}\ensuremath{-}\mathrm{T}}g120{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C})$ would be critical for the excellent properties. A significant effect of the chemical substitution of $\mathrm{I}{\mathrm{n}}^{3+}$ and $\mathrm{Z}{\mathrm{r}}^{4+}$ in PMN-PT to give PIN-PZ-PMN-PT is the development of local strain heterogeneity, which acts to suppress the development of macroscopic shear strains without suppressing the development of local ferroelectric moments and contribute substantially to the RFs in PIN-PZ-PMN-PT. Measurements of elastic and anelastic properties by resonant ultrasound spectroscopy show that PIN-PZ-PMN-PT crystal has a quite different form of elastic anomaly due to Vogel-Fulcher freezing, rather than the a discrete cubic-$T$ transition seen in a single crystal of PMN-28PT. It also has high acoustic loss of the relaxor phase down to ${T}_{\mathrm{R}\ensuremath{-}\mathrm{T}}$. Analysis of piezoresponse force microscopy phase images at different temperatures provides a quantitative insight into the extent to which the RFs influence the microdomain structure and the short-range order correlation length $\ensuremath{\langle}\ensuremath{\xi}\ensuremath{\rangle}$.

Effect of microstructure on the hardness heterogeneity of dissimilar metal joints between 316L stainless steel and SS400 steel

The dissimilar weld joints between 316L austenitic stainless steel and SS400 ferritic steel were used to investigate the effect that microstructure exerts on hardness heterogeneity in weld joints. In order to identify the constituent phases and deformation mechanisms in the dissimilar weld joints, microstructure characterization of undeformed and deformed specimens was conducted via optical microscope (OM), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM) techniques. Micro-hardness measurements across the different weld regions and mini-tension testing combined with digital image correlation (DIC) were conducted to evaluate the mechanical properties of the base metals (BMs), the weld zone (WZ), and the heat-affected zone (HAZ). Local strain heterogeneity on deformed specimens was also explained by microstructure heterogeneity in terms of grain morphology and constituent phases. Non-uniform enhancements of the strain distributions were distinct in the WZ, which consisted of a dendritic structure with a irregular morphologies. Uneven patterns of a martensite transformation from γ to α′ in the 316L contributed to localized heterogeneity in the strain distribution.

Effect of composition and pressure on the shear strength of sodium silicate glasses: An atomic scale simulation study.

The elastoplastic behavior of sodium silicate glasses is studied at different scales as a function of composition and pressure, with the help of quasistatic atomistic simulations. The samples are first compressed and then sheared at constant pressure to calculate yield strength and permanent plastic deformations. Changes occurring in the global response are then compared to the analysis of local plastic rearrangements and strain heterogeneities. It is shown that the plastic response results from the succession of well-identified localized irreversible deformations occurring in a nanometer-size area. The size and the number of these local rearrangements, as well as the amount of internal deviatoric and volumetric plastic deformation, are sensitive to the composition and to the pressure. In the early stages of the deformation, plastic rearrangements are driven by sodium mobility. Consequently, the elastic yield strength decreases when the sodium content increases, and the same when pressure increases. Finally, good correlation was found between global and local stress-strain relationships, reinforcing again the role of sodium ions as local initiators of the plastic behavior observed at larger scales.

Electromechanical Response of Polycrystalline Barium Titanate Resolved at the Grain Scale

Ferroic materials are critical components in many modern devices. Polycrystalline states of these materials dominate the market due to their cost effectiveness and ease of production. Studying the coupling of ferroic properties across grain boundaries and within clusters of grains is therefore critical for understanding bulk polycrystalline ferroic behavior. Here, three‐dimensional X‐ray diffraction is used to reconstruct a 3D grain map (grain orientations and neighborhoods) of a polycrystalline barium titanate sample and track the grain‐scale non‐180° ferroelectric domain switching strains of 139 individual grains in situ under an applied electric field. The map shows that each grain is located in a very unique local environment in terms of intergranular misorientations, leading to local strain heterogeneity in the as‐processed state of the sample. While primarily dependent on the crystallographic orientation relative to the field directions, the response of individual grains is also heterogeneous. These unique experimental results are of critical importance both when building the starting conditions and considering the validity of grain‐scale modeling efforts, and provide additional considerations in the design of novel ferroic materials.

Note: Dynamic meso-scale full field surface deformation measurement of heterogeneous materials.

A dynamic experiment at mesoscale is developed to measure local deformation and strain in granular materials at high temporal and spatial resolutions. The experimental setup is comprised of a high-speed camera along with a high magnification extension tube. The method is demonstrated by measuring the full field strain across and in the boundary of the crystals at a high temporal resolution in polymer bonded sugar crystals and glass beads filled epoxy particulate composite specimens under dynamic loading. In both cases, the local strain heterogeneity is captured successfully. The measured strain and deformation field can be further used to obtain the relative motion of each crystal, crystal rotation, and the relative displacement between the polymer interface and the crystal, which are very critical to understand the local failure mechanisms in heterogeneous materials.

Magnetostructural coupling behavior at the ferromagnetic transition in double-perovskiteSr2FeMoO6

The ordered double-perovskite $\mathrm{S}{\mathrm{r}}_{2}\mathrm{FeMo}{\mathrm{O}}_{6}$ (SFMO) possesses remarkable room-temperature low-field colossal magnetoresistivity and transport properties which are related, at least in part, to combined structural and magnetic instabilities that are responsible for a cubic-tetragonal phase transition near 420 K. A formal strain analysis combined with measurements of elastic properties from resonant ultrasound spectroscopy reveal a system with weak biquadratic coupling between two order parameters belonging to ${\mathrm{\ensuremath{\Gamma}}}_{4}^{+}$ and $m{\mathrm{\ensuremath{\Gamma}}}_{4}^{+}$ of parent space group $Fm\overline{3}m$. The observed softening of the shear modulus by \ensuremath{\sim}50% is due to the classical effects of strain/order parameter coupling at an improper ferroelastic $({\mathrm{\ensuremath{\Gamma}}}_{4}^{+})$ transition which is second order in character, while the ferromagnetic order parameter $(m{\mathrm{\ensuremath{\Gamma}}}_{4}^{+})$ couples only with volume strain. The influence of a third order parameter, for ordering of Fe and Mo on crystallographic B sites, is to change the strength of coupling between the ${\mathrm{\ensuremath{\Gamma}}}_{4}^{+}$ order parameter and the tetragonal shear strain due to the influence of changes in local strain heterogeneity at a unit cell scale. High anelastic loss below the transition point reveals the presence of mobile ferroelastic twin walls which become pinned by oxygen vacancies in a temperature interval near 340 K. The twin walls must be both ferroelastic and ferromagnetic, but due to the weak coupling between the magnetic and structural order parameters it should be possible to pull them apart with a weak magnetic field. These insights into the role of strain coupling and relaxational effects in a system with only weak coupling between three order parameters allow rationalization and prediction of how static and dynamic properties of the material might be tuned in thin film form by choice of strain contrast with a substrate.