Viscous Deformation Research Articles

Fluid-assisted viscous deformation of pseudotachylyte veins near the frictional-viscous transition of the crust: Insights from the Gavilgarh–Tan Shear Zone, Central India

Fluid-assisted viscous deformation of pseudotachylyte veins near the frictional-viscous transition of the crust: Insights from the Gavilgarh–Tan Shear Zone, Central India

Interrogating an along-strike variation in the evolution and rheology of a large continental strike-slip fault zone

Along-strike variations in lithology, temperature, fluid activity, etc. can induce rheological changes in strike-slip faults that may be recorded by different fault rocks and fabrics. This article interrogates localized formation of granite-derived mylonite in a large strike-slip fault zone in which ultramylonite is the principle granite-derived fault rock to better understand this rock record of faulting. Microtextures show that rate-limiting deformation mechanisms in mylonite were dislocation creep in quartz and diffusion creep in very-fine-grained feldspar aggregates. Microtextures also show that mylonite formation is fully compatible with continuous viscous deformation whereas coeval ultramylonite along strike formed after whole-rock cataclasis at the brittle-viscous transition. Differential stresses determined from quartz aggregates in ultramylonites are 40–150% greater than stresses in mylonites. Hence, mylonites represent a local weak sector within this otherwise relatively strong fault zone. Mylonite formation is correlated with syndeformational chemical alteration as well as quartz microstructures and mineral assemblages indicating elevated deformation temperatures. Not all mylonite samples record significant chemical alteration. Therefore, mylonite formation likely records locally elevated temperatures. These results illustrate how a local shift in deformation conditions can affect the evolution and rheology of a large strike-slip fault zone, and how fault rocks record these processes.

Development of permeable networks by viscous-brittle deformation in a shallow rhyolite intrusion. Part 1: Field evidence

Efficient outgassing of shallow magma bodies reduces the risk of explosive eruption. Silica-rich magmas are too viscous for exsolved gas bubbles to escape the system through buoyant forces alone, and so volatile overpressure is often released through deformation-related processes. Here we present a case study on magma emplacement-related deformation in a shallow (∼500 m depth) rhyolite intrusion (the Sandfell laccolith, Eastern Iceland) to investigate the establishment of degassing (volatile exsolution) and outgassing (gas escape) networks in silicic sub-volcanic intrusions. We observe viscous and brittle deformation features: from vesiculated flow bands that organized into ‘pore channels’ in the ductile regime, to uniform bands of tensile fractures (‘fracture bands’) that grade into breccia and gouge in the brittle regime. Through field mapping, structural analysis, and anisotropy of magnetic susceptibility (AMS) measurements, we show that areas with higher degrees of brittle deformation are proximal to abruptly changing AMS fabrics, and flow band orientations and point to laccolith-wide strain partitioning in the magma. We associate the changes in flow fabrics and the intensity of brittle deformation to the transition from dominantly horizontally flowing magma during initial sill-stacking to up to the NE magma flow linked to the propagation of a trap-door fault from the N to the SE. The establishment of intrusion-scale brittle permeable networks linked to changes in strain partitioning that facilitated magma flow during different stages of laccolith growth would have profoundly assisted the outgassing of the entire laccolith. Magmatic fracturing captures viscous and brittle processes working in tandem as an efficient outgassing mechanism, and should be considered in sub-volcanic intrusions elsewhere.

How surface modification of cellulose nanocrystals affects the crystallization process of poly (β-hydroxybutyrate)

Hydroxyl groups on the surface of cellulose nanocrystals (CNC) are modified by chemical methods, CNC and the modified CNC are used as fillers to prepare PHB/cellulose nanocomposites. The absorption peak of carbonyl group of the modified CNC (CNC-CL and CNC-LA) appears in the FT-IR spectra, which proves that the modifications are successful. Thermal stability of CNC-CL and CNC-LA is better than that of pure CNC. Pure CNC is beneficial to the nucleation of PHB, while CNC-CL and CNC-LA inhibit the nucleation of PHB. The spherulite size of PHB and its nanocomposites increases linearly over time, and the maximum growth rate of PHB spherulite exists at 90 °C. Rheological analysis shows that viscous deformation plays the dominant role in PHB, PHBC and PHBC-CL samples, while the elastic deformation is dominant in PHBC-LA. According to the rheological data, the dispersion of CNC-CL and CNC-LA in PHB is better than that of CNC. This work demonstrates the impact of modified CNC on the crystallization and viscoelastic properties of PHB. Moreover, the interface enhancement effect of modified CNC on PHB/CNC nanomaterials is revealed from the crystallization and rheology perspectives.

Hydration of mafic crustal rocks at high temperature during brittle‐viscous deformation along a strike‐slip plate boundary

AbstractThe Poroshiri ophiolite (Hidaka metamorphic belt, Japan) occurs within a crustal‐scale network of high‐temperature, dextral shear zones that accommodated hundreds of kilometres of displacement due to the opening of the Japan Sea in the Neogene. The opholitic rocks comprise ultramafic, mafic and sedimentary protoliths that have been variably hydrated and metamorphosed. This work investigates the mechanisms and timing of fluid influx relative to viscous deformation in metagabbros and amphibolites deformed during exhumation from granulite‐ to amphibolite‐facies conditions. We consider a range of microstructures, from low strain domains and 1–2 mm thick shear bands to mylonites with a thickness of a few meters. Low strain domains of metagabbros exhibit corona textures with symplectites consisting of pargasitic amphibole (Ed0.7) ‐ anorthitic plagioclase (An80–92) ± orthopyroxene ± clinopyroxene forming around olivine and igneous pyroxene and with similar plagioclase–amphibole‐orthopyroxene ± clinopyroxene granoblastic aggregates in micrometric‐thick fractures. These textures result from hydration under low fluid‐rock ratio, with elevated H2O content only occurring locally (H2O > 1–1.2 wt%). Igneous mineral replacement leads to grain size reduction from 1 mm to ~10 μm. Amphibole exhibits a strong core‐rim zonation primarily controlled by the high diffusivity of Fe, Mg and OH and the low diffusivity of Al. Mineral compositional equilibrium is achieved at the scale of 100–200 μm. In mm‐thick localized shear bands and in metric‐scale mylonitic amphibolites, the heterogeneous mineral composition of amphibole (Ed0.2–0.5) and plagioclase (An40−An80) indicates only partial re‐equilibration (at the scale of 200–500 μm) despite higher fluid‐rock ratios and more pervasive fluid percolation than in metagabbros. Plagioclase–amphibole thermometry and equilibrium phase diagrams indicate that the initial fluid infiltration and corona formation occurred at 800–850°C by fracturing and percolation along grain boundaries. This was followed by the main fluid percolation and mylonitization event, which occurred during exhumation and cooling at conditions of 720–580°C, ~4 kbar. Continuous hydration during retrogression was achieved by the influx of dominantly seawater‐derived fluid, as attested by the high chlorine (Cl) contents (>300–400 ppm) of amphiboles in fractures. The heterogeneous distribution of fractures controls the distribution of fluid from the earliest stages of hydration, creating positive feedback where the growth of hydrous minerals as amphibole (up to +300 vol% of amphibole in high strain areas relative to the low‐strain ones) and the formation of fine‐grained mixed domains that led to further localization of viscous strain and mass transfer (variations of ± 30–40% in major elements). The Poroshiri ophiolite therefore represents a good fossil example of a former transpressional plate boundary where coupled metamorphic and deformation processes were triggered by seawater‐derived fluid that percolated to depths of ~15 km.

Creep behavior of epoxy adhesives subjected to different hygrothermal aging conditions—nanoindentation creep tests and theoretical study

Epoxy adhesives have been extensively used in the aerospace, marine, and automotive industries to join different components. A major concern with the use of epoxy adhesives is their viscoelastic behavior in aggressive service conditions such as hygrothermal ageing. Surveying the creep behavior of adhesives is of paramount importance to increase long-term durability. In this work, nanoindentation creep tests were performed on an epoxy adhesive exposed to distilled water and seawater at 55 °C for various ageing durations (0, 14, 38, 160, 251, 383, 582, and 800 h). The hardness, modulus, creep displacement, and creep rate sensitivity were quantitatively investigated to elucidate the effect of hygrothermal ageing. All the mechanical properties were found to decrease with the ageing time. The adhesive subjected to distilled water showed lower creep resistance due to higher absorption of moisture. In addition, linear relationships were observed between different mechanical properties and moisture contents irrespective of ageing conditions. Subsequently, the generalized Kelvin model was applied to investigate the creep compliance and the dependence of different deformation types (elastic, viscoelastic, and viscous deformation) on the ageing time and ageing conditions. The motion of molecular structures was also discussed. Finally, a modified creep model was proposed based on the generalized Kelvin model and continuum damage theories, which established the relationship between the dry and aged adhesive via the moisture-dependent degradation factors. The predicted creep displacements coincided well with the experimental results for the case, demonstrating the reliability of the creep model.

Correlation analysis of evaluation methods and indicators for low-temperature performance of epoxy asphalt

Selecting an epoxy asphalt (EA) material with excellent low-temperature performance is a challenging task due to that the traditional test methods and indicators for thermoplastic asphalt may not be appropriate for thermosetting EA, and the binders’ low-temperature performance does not always match that of mixtures. The primary purpose of this study is to determine the appropriate low-temperature evaluation methods and indexes of EA materials and the correlation between the low-temperature performance of EA binder and EA mixture (EAM). First, the low-temperature performance of four EA binders was analyzed using tensile, bending beam rheometer (BBR), and dynamic mechanical analysis (DMA) tests. Then, the low-temperature cracking resistance of the EAMs was evaluated through beam bending and semi-circular bend (SCB) tests. Finally, Pearson correlation analysis was performed separately on the low-temperature indicators of EA binders and EAMs. Moreover, the Grey correlation analysis was employed to determine the correlation between the low-temperature properties of the two. The results showed that the correlation between fracture elongation (ε) and other test indicators was not significant. The multiple indicators of the BBR, such as viscoelastic parameters, viscous deformation ratio (JR), along with the glass transition temperature (Tg) of the DMA, showed consistent evaluation results for the low-temperature performance of the four EA binders. However, the correlation of these indicators with the cracking resistance of the EAM was notably different. The flexural strain energy density of the beam bending test and SCB fracture energies demonstrated excellent correlation. The grey correlation analysis results of these two indicators as reference series were highly similar. Specifically, the novel JR in this study and the Tg exhibited a better correlation with the low-temperature cracking resistance of EAM. These two indicators were preferentially recommended for the evaluation of the low-temperature performance of EA and the prediction of the low-temperature cracking resistance of EAM.

Modeling Analysis of Complex Deformation of Woven Coating Film during the Cyclic Tensile Process.

It is difficult for the existing Burgers model to accurately depict the off-axis cyclic drawing process of woven coatings. In this paper, the mechanical deformation of woven PVC (polyvinyl chloride)-coated film at different temperatures is investigated. One-dimensional (1D) and two-dimensional (2D) constitutive models were established to characterize cyclic deformation processes. The 1D model is an improved Burgers model. The effects of the time dependence of the viscosity coefficient and the ratio of elastic to viscous deformation are considered simultaneously. The accuracy of the 1D model for predicting the cyclic nonlinear deformation at different temperatures and loading rates is improved. The 2D model is a nonlinear orthotropic model using polynomials. On the basis of the single-objective genetic algorithm, the inverse algorithm is used to obtain the shear polynomial coefficients in the tension phase and the shear modulus in the unloading phase, which circumvents performing the difficult shear test. UMAT subroutines of off-axis stretching and off-axis cyclic stretching are written separately. The intelligent inverse algorithm program consists of a single-objective genetic algorithm program, a finite element parametric modelling program, and a UMAT subroutine. The simulation results are compared with the off-axis cyclic tensile test data to validate the effectiveness and accuracy of the proposed 2D model for the analysis of the woven PVC-coated films in the tension-shear coupling state.

Modelling of Multicomponent Fluid Flow in Deforming and Reacting Porous Rock

We propose a coupled hydro-chemo-mechanical model and its 1D numerical implementation. We demonstrate its application to model filtration of a multicomponent fluid in deforming and reacting host rocks, considering changes in the densities, phase proportions and chemical compositions of coexisting phases. We presented 1D numerical implementation on the example of soapstone formation from serpentinite during H₂O-СО2 fluid filtration with low concentration of СО2 coupled with viscous deformation of mineral matrix, considering MgO-SiO2-H₂O-СО2 system. The numerical results show porosity wave propagation by viscous (de)compaction mechanism accompanied with the formation of an elongated zone with higher filtration properties. After the formation of such a channel, the formation and propagation of reaction fronts occurs associated with the transformation of the mineral composition of the original rock. During H2O-CO2 fluid filtration, starting from 1 weight percent of dissolved CO2, carbonization of hydrated serpentinite starts, specifically antigorite transforms to magnesite and talc.

A modified viscous flow law for natural glacier ice: Scaling from laboratories to ice sheets

Glacier flow modulates sea level and is governed largely by the viscous deformation of ice. Multiple molecular-scale mechanisms facilitate viscous deformation, but it remains unclear how each contributes to glacier-scale deformation. Here, we present a model of ice deformation that bridges laboratory and glacier scales, unifies existing estimates of the viscous parameters, and provides a framework for estimating the parameters from observations and incorporating flow laws derived from laboratory observations into glacier-flow models. Our results yield a map of the dominant deformation mechanisms in the Antarctic Ice Sheet, showing that, contrary to long-standing assumptions, dislocation creep, characterized by a value of the stress exponent [Formula: see text], likely dominates in all fast-flowing areas. This increase from the canonical value of [Formula: see text] dramatically alters the climate conditions under which marine ice sheets may become unstable and drive rapid rates of sea-level rise.

Phenomena-based optimization of load function during nanoindentation experiments for estimating elastic aspect of viscous materials

We propose an optimized load function designed to acquire the elastic aspect during nanoindentation for two viscous polymers, i.e., polycarbonate (PC) and poly (methyl methacrylate) (PMMA). To do so, various load functions are followed where constant strain rate (P˙/P) varies from 0.05 /s to 50.0 /s, maximum load (Pm) from 1000 μN to 9000 μN and unloading rate (P˙UL) from 9.0 × 102 μN/s to 107 μN/s. Depending upon the P˙/P, extent of viscous deformation varies during loading, e.g., slow P˙/P shows more viscous deformation due to sufficient loading time and vice-versa. However, for fast P˙/P, a large amount of viscous deformation is observed only when the tip decelerates at the end of loading since the deceleration zone is the favor of viscous deformation. During holding, it is seen that a large amount of viscous deformation takes place for fast P˙/P at any Pm. Because viscous deformation could not take place during loading due to insufficient time that is why it takes place during holding. In addition, at high Pm large amount of viscous deformation takes place than low Pm. Since it is observed that different time is required for various P˙/P and Pm to saturate the viscous deformation during holding; hence, a novel method is suggested to estimate the required time for any P˙/P and Pm indentation. During unloading, it is noticed that for fast P˙UL less amount of viscoelastic recovery takes place towards Pm, hence, it is recommended that 95%–40% and 95%–60% unloading range should be considered to evaluate the elastic aspect for PC and PMMA, respectively.

Comparative Analysis and Error Assessment of Nanoindentation Evaluation Techniques for NafionTM117

AbstractAdvances in the application of polymers for electrochemical cells require an understanding of their viscous deformation mechanisms and their interaction with moisture. Nanoindentation offers a localized, microscale testing alternative to traditional tensile testing. However, the viscoelastic nature of the polymers, combined with their increased compliance, presents challenges in the analysis of nanoindentation results. In addition, the dependence on moisture results in significant scatter and low repeatability. This study combines nanoindentation and tensile testing as a verification method and compares different correction protocols for static nanoindentation to investigate the mechanical behavior of polymer electrolyte membranes. Comparisons of different indentation devices, analysis methods, and indentation protocols show a significant overestimation of Young’s modulus using the classical Oliver–Pharr method compared to values determined from tensile tests. Nanoindentation at different humidity levels revealed different mechanisms leading to a decrease in Young’s modulus and hardness with increasing humidity.

A nonlinear finite viscoelastic formulation relative to the viscous intermediate configuration applied to plants

AbstractIn the contribution at hand, a new formulation for finite strain viscosity relative to the viscous intermediate configuration is presented. The evolution of the viscous deformations is based upon a new numerical approach, which allows for a consistent consideration of anisotropic finite strain viscoelasticity, according to the authors knowledge. A standard Maxwell model is used to describe viscous behaviour at finite deformations. Furthermore, the orthotropic Yeoh material model is extended to include a distinction between behaviour under tensile and compression loading. The proposed formulation is validated, and parameters of the model are identified by material tests on Sorghum bicolor plants. Subsequently, numerical examples are shown to demonstrate the capabilities of the model. In general, the proposed Yeoh material formulation is shown to accurately represent the inability of fibres to carry compression loading. Furthermore, the viscoelastic approach, developed relative to the viscous intermediate configuration, is demonstrated to be capable of producing plausible results. Additionally, the mechanical behaviour of Sorghum bicolor plants is simulated using the introduced formulation. The results show that the contribution at hand describes a novel methodology to simulate the viscoelastic behaviour of plant materials reliably.

A pressure solution flow law for the seismogenic zone: Application to Cascadia.

We develop a linear viscous constitutive relationship for pressure solution constrained by models of deformed metasedimentary rocks and observations of exposed rocks from ancient subduction zones. We include pressure and temperature dependence on the solubility of silica in fluid by parameterizing a practical van't Hoff relationship. This general flow law is well suited for making predictions about interseismic behavior of subduction zones. We apply the flow law to Cascadia, where thermal structure, geometry, relative plate velocity, and Global Positioning System velocity field are well constrained. Results are consistent with the temperature conditions at which resolvable ductile strain is recorded in subducted mudstones (at depths near the updip limit of the seismogenic zone) and with relative plate motion accommodated completely by viscous deformation (at depths near the downdip limit of the seismogenic zone). The flow law also predicts the observed forearc tapering of slip rate deficit with depth.

Ascent and emplacement controls of mafic magmas in the mid crust − evidence from 3D modelling of basic bodies of the Koperberg Suite, Namaqualand

Abstract The 3D modelling of basic bodies of the Koperberg Suite (1060 to 1030 Ma) and their wall rocks from Narrap Mine illustrates the distribution, geometries and, by implication, processes that determined the ascent and emplacement of the mantle-derived mafic magmas into the partially-molten, mid-crustal granite-gneiss sequence of the Okiep Copper District in Namaqualand. The lens-like, discontinuous geometry of basic bodies suggests the transfer of the mafic magmas as self-contained, buoyancy-driven hydrofractures. The presence of both shallowly-dipping, foliation-parallel sills and subvertical lenses in zones of steep foliation development, so-called steep structures, indicates an emplacement of the mafic magmas under low deviatoric stresses and irrespective of the regional stress field. Instead, the emplacement of the mafic magmas parallel to pre-existing anisotropies (tectonic fabrics or lithological contacts) highlights those differences in tensile strength and fracture toughness parallel to or across anisotropies determined the propagation of the magmas. This also accounts for the common occurrence of basic bodies in steep structures in which the vertical gneissosity promoted the buoyancy-driven ascent of the mafic magmas. On a regional scale, the mechanical stratification of the subhorizontal, sheet-like granite gneisses and interlayered metasediments exerted important controls on the ascent of Koperberg Suite magmas. The preferential emplacement of basic bodies in schist and gneiss units suggests that the lower rigidity of the ductile wall rocks facilitated magma emplacement through a combination of viscous wall-rock deformation and fracture blunting that led to the arrest of the magma-filled hydrofractures. Multiple intrusive relationships of successively emplaced magma batches suggest that later magmas reutilised earlier established magma pathways, particularly in steep structures. High-rigidity lithologies, such as the massive Springbok Quartzite, in contrast, only allowed for smaller fracture apertures and limited dilation, resulting in the pinching of basic bodies and rather stringer-like geometries. It is conceivable that the higher fracture toughness of the quartzite may also have prevented propagation of the mafic magmas through the Springbok Quartzite and, instead, led to the ponding of basic bodies below the metasediments. The geometry and structural and lithological controls of basic bodies at Narrap Mine are similar to Koperberg Suite intrusions documented from many of the other mine workings in the Okiep Copper District. This suggests similar underlying emplacement controls of the cupriferous rocks, which can be extrapolated on a regional scale and that may guide exploration.

Intrusion tip velocity controls the emplacement mechanism of sheet intrusions

Space for intruding magma is created by elastic, viscous, and/or plastic deformation of host rocks. Such deformation impacts the geometries of igneous intrusions, particularly sills and dikes. For example, tapered intrusion tips indicate linear-elastic fracturing during emplacement, whereas fluidization of host rocks has been linked to development of elongate magma fingers with rounded tips. Although host rock fluidization has only been observed at the lateral tips of magma fingers, it is assumed to occur at their leading edges (frontal tips) and thereby control their propagation and geometry. Here, we present macro- and microstructural evidence of fluidized sedimentary host rock at the lateral tips of magma fingers emanating from the Shonkin Sag laccolith (Montana, western United States), and we explore whether fluidization could have occurred at their frontal tips. Specifically, we combine heat diffusion modeling and fracture tip velocity estimates to show that: (1) low intrusion tip velocities (≤10−5 m s−1) allow pore fluids ahead of the intrusion to reach temperatures sufficient to cause fluidization, but (2) when tip velocities are high (∼0.01−1 m s−1), which is typical for many sheet intrusions, fluidization ahead of propagating tips is inhibited. Our results suggest that intrusion tip velocity (i.e., strain rate) is a first-order control on how rocks accommodate magma. Spatially and temporally varying velocities of lateral and frontal tips suggest that deformation mechanisms at these sites may be decoupled, meaning magma finger formation may not require host rock fluidization. It is thus critical to consider strain rate and three-dimensional intrusion geometry when inferring dominant magma emplacement mechanisms.

TIME DEPENDENT DEFORMATIONS OF A COUPLED BRIDGE: A CASE STUDY

<p>The bridge's span structure comprises a connected beam designed to support a concrete slab poured over parallel steel supports. Simultaneously, segmental construction, shrinkage, and the flow of concrete play a significant role in stress redistribution over time. The span construction is statically indeterminate due to its connections with the abutments, and temporal deformations occur under additional complex conditions. In this analysis, we employed a calculation model based on the layered finite elements method developed by the authors. This model can be utilized to analyse both statically indeterminate supports and the predicted phased construction method. It accounts for changes in the static system and loading, as well as variations in the layers within the coupled section and the viscous properties of the concrete over time. The calculation analysis results reveal that viscous concrete deformations, combined with different moments of activation of individual segments, have a significant impact on stress redistribution over time. Such intricate analyses are indispensable for ensuring the required safety and cost-effectiveness of the bridge span construction.</p>

The UTUH model: a time-dependent unified hardening constitutive model for unsaturated soils

AbstractAn advanced constitutive framework for unsaturated soils, the UTUH model, is proposed in this paper, which considers the joint effect of time, suction and overconsolidation within the framework of sub-loading surface plasticity. A reference line, namely the instantaneously normal compression line (INCLs) for unsaturated soils, is introduced from a conceptual framework drawn from constant rates of strain test results to determine creep time and overconsolidation states of unsaturated soils. Subsequently, an isotropic elasto-viscoplastic constitutive model for unsaturated soils is produced by combining viscous deformation with mechanical and hydraulic deformation through overconsolidation parameter. Net stress, suction and time are adopted as fundamental constitutive variables and time-dependent loading collapse yield surface is derived to characterize the relationship between yield stress, suction, and time. Then, an extension to a triaxial stress state is built in the space of mean effective stress, suction, deviator stress and time variable. The hardening of yield surface and sub-loading surface is controlled by viscoplastic volumetric strain and unified hardening parameter. The performance of the proposed UTUH model is addressed through four numerical studies, and the proposed model is validated against experimental data from the literature.

Nonlinear anisotropic viscoelasticity

In this paper, we revisit the mathematical foundations of nonlinear viscoelasticity. We study the underlying geometry of viscoelastic deformations, and in particular, the intermediate configuration. Starting from the direct multiplicative decomposition of the deformation gradient ▪ , into elastic and viscous distortions ▪ and ▪ , respectively, we point out that ▪ can be either a material tensor ( ▪ is a two-point tensor) or a two-point tensor ( ▪ is a spatial tensor). We show, based on physical grounds, that the second choice is unacceptable. It is assumed that the free energy density is the sum of an equilibrium and a non-equilibrium part. The symmetry transformations and their action on the total, elastic, and viscous deformation gradients are carefully discussed. Following a two-potential approach, the governing equations of nonlinear viscoelasticity are derived using the Lagrange–d’Alembert principle. We discuss the constitutive and kinetic equations for compressible and incompressible isotropic, transversely isotropic, orthotropic, and monoclinic viscoelastic solids. We finally semi-analytically study creep and relaxation in three examples of universal deformations.

Quantification of high temperature stability of mineral wool for fire-safe insulation

Mineral wool, particularly stone wool, is a widely applied thermal insulation material that plays a critical role both in saving energy and in slowing the spread of fire in buildings owing to its high-temperature stability (HTS). However, so far there has been a lack of a universal method to accurately quantify HTS of mineral wool on a small scale. Here, we established a universal method, which is based on measuring the variation of the silhouette area of a cylindrical wool fiber pellet during heating by a hot-stage microscope. Using this method, we detected two main stages of shrinking: 1) the first-stage shrinking related to viscous deformation; 2) the second-stage shrinking caused by melting. Minimizing the first stage shrinking is the key to ensure the fire barrier role of stone wool. The origin of the HTS differences among different types of wool products was clarified by X-ray diffraction, differential scanning calorimetry and thermal expansion.