Brittle Regime Research Articles

The Analysis of Low Temperature Toughness on X80 Pipeline Steel Welded Joint

Aiming at the security problems of pipeline steel application, the different positions of the welded joints of circumferentially welding pipeline of X80 steel were investigated by microstructure observation, the hardness, Charpy impact toughness and crack tip opening displacement (CTOD) test at low temperature. The Vickers hardness test results show that there are local softened regions in heat-affected zone (HAZ). Charpy impact test indicate that the ductile–brittle transition temperature of weld is below − 60 °C, the ductile–brittle transition temperature of HAZ is around − 38 °C. CTOD test reveal that the fracture toughness of HAZ shows a large fluctuation since it is in the ductile–brittle transition temperature regime.

Tuning the creep rates of binary Al alloys by considering the effects of the stacking faults, alloying elements, and elastic moduli: a first-principles study

Using first-principles calculations, the effects of intrinsic stacking faults, elastic moduli, and diffusivity on the creep rates of aluminum alloys Al–X (X = Sc, Nb, or Mo) have been investigated. The calculated stacking fault energies of dilute Al show stabilization in the case of Sc and destabilization in the case of Mo and Nb. Although all three impurities confer stiffer elastic properties, Sc appears to retain the ductility of Al but Mo and Nb push the system in the brittle regime. Also, Mo and Nb strongly increase the activation barrier to diffusion, leading to much reduced creep. The results indicate that Mo and Nb can be used in Al alloys to improve elastic properties and creep resistance but only at very low levels, before brittleness becomes an issue.

Microstructural Control of Physical Properties During Deformation of Porous Limestone

AbstractWe performed triaxial deformation experiments in Purbeck limestone (13.8% average porosity) across the brittle‐ductile transition and monitored the evolution of permeability and wave velocities as a function of strain. In the brittle regime, the rock yields in dilation. In the ductile regime, the rock first yields in compaction and then undergoes net dilation at some critical level of strain. The permeability increases after failure in the brittle regime and decreases with increasing compaction in the ductile regime. The wave velocities decrease with increasing strain, and the material becomes transversely isotropic. At axial strains of the order of 5%, the anisotropy parameters (from Thomsen, 1986) are around ε ≈ −0.2 and δ ≈ decrease with increasing axial strain beyond the yield point−0.3. Under hydrostatic conditions, the rock also yields in compaction. The hydrostatic yield point is not marked by any significant drop or increase in wave velocity during loading, but wave velocities decrease (and therefore crack density increases) significantly upon unloading. In all our tests, the permeability change is proportional to the initial porosity change until the point of net dilation is reached. The strain at that point also acts as a scaling factor for the relative drop in P and S wave velocities during deformation. All our experimental data point to a disconnection between the evolution of permeability, porosity, and wave velocities during deformation in the ductile regime: permeability is controlled by a fraction of the micropore network, while wave velocities are mostly influenced by microcracks that do not contribute significantly to either the total rock porosity or fluid flow properties.

Subduction Thermal Regime, Slab Dehydration, and Seismicity Distribution Beneath Hikurangi Based on 3‐D Simulations

AbstractThe downdip limit of seismogenic interfaces inferred from the subduction thermal regime by thermal models has been suggested to relate to the faulting instability caused by the brittle failure regime in various plate convergent systems. However, the featured three‐dimensional thermal state, especially along the horizontal (trench‐parallel) direction of a subducted oceanic plate, remains poorly constrained. To robustly investigate and further map the horizontal (trench‐parallel) distribution of the subduction regime and subsequently induced slab dewatering in a descending plate beneath a convergent margin, we construct a regional thermal model that incorporates an up‐to‐date three‐dimensional slab geometry and the MORVEL plate velocity to simulate the plate subduction history in Hikurangi. Our calculations suggest an identified thrust zone featuring remarkable slab dehydration near the Taupo volcanic arc in the North Island distributed in the Kapiti, Manawatu, and Raukumara region. The calculated average subduction‐associated slab dehydration of 0.09 to 0.12 wt%/km is greater than the dehydration in other portions of the descending slab and possibly contributes to an along‐arc variation in the interplate pore fluid pressure. A large‐scale slab dehydration (>0.05 wt%/km) and a high thermal gradient (>4 °C/km) are also identified in the Kapiti, Manawatu, and Raukumara region and are associated with frequent deep slow slip events. An intraslab dehydration that exceeds 0.2 wt%/km beneath Manawatu near the source region of tectonic tremors suggests an unknown relationship in the genesis of slow earthquakes.

The effects of water on the strength of black sandstone in a brittle regime

The mechanical behavior of rock is significantly affected by water. To further study the influence of water on the mechanical behavior of rocks, uniaxial compressive loading experiments were performed on black sandstone specimens (collected at a site in Longchang, Sichuan Province, China) with different water contents. The water absorption was first tested to study the evolution of the water content in the specimens. Then, the mechanical behaviors of the specimens after different durations of soaking in water (from dry to saturation) were tested under uniaxial compression. The results showed that, in the stress-strain curves for the specimens, the initial slope and strength decrease with increasing soaking duration and that the curves are strongly nonlinear in the prepeak region. Furthermore, with increasing water content, the elastic modulus and uniaxial compressive strength decrease, while the Poisson's ratio increases. A comprehensive set of predictive empirical relationships is established between the mechanical properties and the water content/soaking duration for the black sandstone. As the soaking duration increases, the failure pattern gradually changes from tensile to shear-dominated failure. A novel observation is that, for two specimens with the same water content, the strength of a specimen with a homogeneous water distribution is lower than that of a specimen with a non-homogeneous water distribution. The results suggest that the water soaking duration, water distribution and loading-saturation sequence of a rock should all be considered in experiments to gain a deeper understanding of the mechanical responses of rocks with different water contents.

Fluid composition changes in crystalline basement rocks from ductile to brittle regimes

Abstract The relationships between deformation and fluid flow have been investigated in the Paleozoic basement of an isolated horst of the Catalan Coastal Ranges. A structural, petrological and geochemical study has been performed in a complex fracture network that resulted from a long-lived tectonic history (from Carboniferous to Miocene). Nine fracture types, developed from a ductile regime in the greenschist facies to a shallow brittle regime, have been characterized in order to establish P, T and fluid compositions during the evolution of the horst. Syn-cleavage and late-cleavage quartz veins (qtz1-chl1 ± mu and late qtz2-chl2-dol1) formed during the Hercynian ductile deformation. These minerals precipitated from metamorphic fluids, possibly evolved from seawater, at temperatures between 240 and 340 °C. En-echelon albite vein arrays (ab-qtz3-chl3 ± ti-an) and NE-SW normal faults generating breccias mark the change from ductile to brittle, from compression to extension and from a closed to an open hydrologic regime. This paragenesis precipitated from the mixing of metamorphic and magmatic fluids at temperatures between 180 and 290 °C during the early Permian extension. Dolomite veins (dol2-chl4-qtz4), precipitated at 210–280 °C from the mixing of previous fluids with hypersaline oxidizing external brines, possibly during the late stage of the early Permian extension. Reverse faults and calcite veins (Cc1-ba) formed either during the Paleogene compression or during the Langhian to early Serravallian minor compression. Calcite and barite precipitated from meteoric or marine waters in an open hydrological system at temperatures below 50 °C. The Miocene extension is represented by NE-SW normal faults with fault gouges and NNW-SSE normal faults cemented by calcite 2 that precipitated at temperatures below 50 °C from meteoric fluids in an open basin-scale hydrological system. The studied horst was part of a relay zone between two segments of the NNW-SE Llobregat fault during the early Permian, explaining the high fracture density and the fast upflowing of hydrothermal fluids at that time, thus controlling the development of albite veins exclusively in this area.

Estimation of the uniaxial compressive strength of Arctic sea ice during melt season

A series of uniaxial compressive tests using ice cores collected in the Arctic Ocean was conducted in the cold laboratory on board R/V Xuelong during the summers of 2012 and 2014. A total of 130 ice samples were tested at temperatures ranging from −9 °C to −3 °C at strain rates ranging from 10−7 s−1 to 10−2 s−1 with the loading direction along the core axis. The uniaxial compressive strength of sea ice depends mainly on two parameters: sea ice porosity and strain rate during the test. Arctic sea ice presented characteristics of weak porosity effect and low transition strain rate. The effect of strain rate on the uniaxial compressive strength could be parameterized using a piecewise function for ductile, transition and brittle regimes. A power-law relationship was found between the uniaxial compressive strength of ice samples and their porosity. These relationships made it feasible to estimate the natural uniaxial compressive strength of ice as a function of in-situ porosity and strain rate. The results derived from the ice samples were extended to large-scale strength of ice sheets based on their porosity profiles determined using field measurements of ice physical properties. The strength of Arctic ice sheets in the summers of 2012 and 2014 was far less than previous estimates, probably because of accelerated interior ice melt caused by Arctic warming.

Feature learning method of acoustic emission signal during single-grit scratching on BK7 in brittle regime

Acoustic emission (AE) signal is released from a material as it undergoes deformation and fracture processes. AE signal provides enough information for monitoring of the interaction between tool and material. AE RMS, AE count rates, and frequency characteristics are always employed in AE-based monitoring techniques. Monitoring sensitivity is not satisfied because information implies in AE signal is lost or weaken to some extent for the present monitoring parameters. When a hard-brittle material is removed in brittle regime, burst-type AE (b-AE) associated with crack and chip is predominant compared with low-amplitude continuous-type AE. It will be more objective and physically meaningful if b-AE event is taken as a unit to be monitored. This paper is dedicated to the method of monitoring b-AE event in AE signal. Ignoring background noise, an AE signal can be looked as a convolution of b-AE events and corresponding coefficients. b-AE events correspond to brittle transient behaviors and include information of fracture mechanism. Coefficients represent intensity and location of crack and chip during removal processes. The two elements of the convolution contain different aspects of signal feature. Considering randomness of AE signals, the convolution form will be realized by self-learning from training data set of AE signals. Dictionary-learning algorithm for decaying oscillation modes of b-AE and sparse representation procedure of an AE signal are detailed in this paper based on the convex optimization theory. AE signals in brittle regime are acquired from tests of single diamond grit scratching on BK7. Simulation and experimental results verify the correctness of the feature learning method. According to the method proposed in this paper, b-AE can be objectively monitored without the interference of varying machining parameters.

Alkali metasomatism as a process for Ti–REE–Y–U–Th mineralization in the Saghand Anomaly 5, Central Iran: Insights from geochemical, mineralogical, and stable isotope data

The Saghand Anomaly 5 is located in the Bafq-Saghand metallogenic province in the Central Iranian geostructural zone and contains Ti, REEs, Y, U, and Th mineralization. The mineralization is related to alkali-metasomatism and occurs in peripheral alteration zones around the iron ore deposits. Alkali-metasomatism and mineralization were controlled by tectonic activity along fault zones from ductile to brittle regimes of deformation. A metasomatic zoning is developed from outermost unaltered lithologies (subvolcanic diorite and quartz diorite host rocks) inwards to albite-actinolite metasomatite, phlogopite-actinolite metasomatite, and ultimately to magnetite orebodies. The last widespread hydrothermal event corresponds to an epidote2 ± chlorite ± calcite2 ± quartz paragenesis superimposed on all previous mineral associations.Microscopy studies reveal that ilmenite, davidite, allanite-(La), Ti–Y–U–Th-Oxide, REE-Oxide, rutile, and titanite and lesser amounts of thorite are ore minerals of Saghand Anomaly 5. The Ti–REE–Y–U–Th mineralization is related to Na–Ca-metasomatism and Ca-alteration and occurs as disseminated in albite-actinolite metasomatites and locally as veinlet-type in aplites and granites.The geochemical investigations indicate a calc-alkaline and continental-margin arc setting for granite and associated diorite-quartz diorite host rocks in the Saghand Anomaly 5. The REE patterns of the mineralized metasomatites show LREE enrichment and strong Eu negative anomalies. The presence of REE-rich hydrothermal phases suggests a significant mobilization and deposition of REEs, especially La, Ce and Y, by high temperature hydrothermal solutions within the Saghand Anomaly 5.The measured temperatures range from ∼748° to ∼766° C and ∼703° to ∼737° C for Na–Ca-metasomatic and K–Ca-metasomatic stages, respectively, using the magnetite1-actinolite and magnetite2-phlogopite oxygen isotope pairs, respectively. Both δD and δ18O values of actinolite and phlogopite indicate a magmatic source of actinolite and phlogopite forming fluids. In addition, C and O isotopic data of calcite2, from the late veinlets, indicate a magmatic origin of fluids in equilibrium with calcite2 and the formation temperature of 350 to 400° C.

Earthquake induced soft sediment deformation structures in the Paleoproterozoic Vempalle Formation (Cuddapah basin, India)

Soft sediment deformation structures (SSDS) are preserved in a homogenous dolomudstone lithology of crinkly laminated and heterolithic facies of the Paleoproterozoic Vempalle Formation in the Cuddapah Basin. This basin was formed on the eroded basement rocks of the Eastern Dharwar Craton, India. Deformation structures preserved in this succession include combination of breccia and folds, intrastratal faults, cracks, and dikes belonging mostly to a brittle deformation regime associated with ductile imprints. Based on the observed SSDS, their lateral homogeneity and traceability, draping by undeformed strata, proximity of faults as well as apparent lack of storm signatures and gravity induced mass movement, these fine-grained deformed beds can be tentatively ascribed to a large to intermediate depth earthquake with Richter magnitude scale 4 and above, generated during reactivation of basement faults owing to plume related mantle activity. The occurrence of SSDS in the Vempalle Formation emphasizes the role of downwarping along pre-existing planes of weakness in the Archean basement in the evolution of the Cuddapah Basin, analogous to subsidence in present-day continental margin.

Grinding performance of TiCp/Ti-6Al-4V composites with CBN wheels, part I: experimental investigation and surface features

This article presents a comparison study on the machining performance of particulate reinforced titanium matrix composites (PTMCs) in conventional speed grinding (CSG) and high speed grinding (HSG) using monolayer brazed CBN wheels. Grinding forces, temperature and ground surface topology have been analyzed. It is discovered that the grinding forces in CSG are higher than those in HSG. However, grinding temperature in HSG is higher. Grinding scratches and concavities are the dominant ground surface features in both the CSG and HSG. The machined surface obtained in HSG is smoother than that obtained in CSG. The material removal mechanism of PTMCs include ductile removal regime of the metallic matrix and brittle removal regime of the TiC reinforced particles in grinding.

Grinding performance of TiCp/Ti-6Al-4V composites with CBN wheels, part II: material removal behavior based on FEM

In order to understand the material removal behavior of TiCp/Ti-6Al-4V particulate reinforced titanium matrix composites (PTMCs) during conventional speed grinding (CSG) and high speed grinding (HSG), a 3D finite element (FE) model has been established. Based on the FE model, the material removal behavior and the influence of grinding speed on the formation of machined surface feature were discussed. The results show that the material removal behavior in grinding of PTMCs can be divided into ductile regime removal of the metal matrix materials and brittle regime removal of the TiC reinforced particles. The ductile regime removal is dominated by serrated chip formation. The brittle regime removal is dominated by brittle fracture, crack initiation, crack propagation. The grinding speed has a considerable influence on the ground surface features. The ground surface morphology obtained in CSG is more complex and poorer than that obtained in HSG.

Fabric transition with dislocation creep of a carbonate fault zone in the brittle regime

Fabric transition by a switch in the dominant slip system of minerals in the plastic regime can be induced by changes in temperature, strain rate, or water content. We propose here this fabric transition by frictional heating in seismogenic fault zones in the brittle regime. The Garam Thrust in the Taebaeksan Basin of South Korea has a hanging wall of Cambrian dolostone juxtaposed against a footwall of Ordovician limestone and records a minimum displacement of ~120m. In a 10cm thick plastically deformed layer adjacent to the principal slip layer of the fault zone, the lattice preferred orientation of calcite grains suggests that the dominant slip system changes, approaching the principal slip layer, from r 〈02–21〉 and e-twinning, through r 〈02–21〉 and basal 〈a〉, to basal 〈a〉. This fabric transition requires a high temperature-gradient of 40°C/cm, which we infer to result from frictional heating of the seismic fault zone. We suggest that fabric transition within a thin plastically deformed layer adjacent to the principal slip layer of a fault zone indicates an unusually steep temperature gradient and provides strong evidence of seismic slip.

Three‐Dimensional Seismic Structure of the Mid‐Atlantic Ridge: An Investigation of Tectonic, Magmatic, and Hydrothermal Processes in the Rainbow Area

AbstractTo test models of tectonic, magmatic, and hydrothermal processes along slow‐spreading mid‐ocean ridges, we analyzed seismic refraction data from the Mid‐Atlantic Ridge INtegrated Experiments at Rainbow (MARINER) seismic and geophysical mapping experiment. Centered at the Rainbow area of the Mid‐Atlantic Ridge (36°14'N), this study examines a section of ridge with volcanically active segments and a relatively amagmatic ridge offset that hosts the ultramafic Rainbow massif and its high‐temperature hydrothermal vent field. Tomographic images of the crust and upper mantle show segment‐scale variations in crustal structure, thickness, and the crust‐mantle transition, which forms a vertical gradient rather than a sharp boundary. There is little definitive evidence for large regions of sustained high temperatures and melt in the lower crust or upper mantle along the ridge axes, suggesting that melts rising from the mantle intrude as small intermittent magma bodies at crustal and subcrustal levels. The images reveal large rotated crustal blocks, which extend to mantle depths in some places, corresponding to off‐axis normal fault locations. Low velocities cap the Rainbow massif, suggesting an extensive near‐surface alteration zone due to low‐temperature fluid‐rock reactions. Within the interior of the massif, seismic images suggest a mixture of peridotite and gabbroic intrusions, with little serpentinization. Here diffuse microearthquake activity indicates a brittle deformation regime supporting a broad network of cracks. Beneath the Rainbow hydrothermal vent field, fluid circulation is largely driven by the heat of small cooling melt bodies intruded into the base of the massif and channeled by the crack network and shallow faults.

Seismicity in the Vicinity of the Tristan Da Cunha Hot Spot: Particular Plate Tectonics and Mantle Plume Presence

AbstractEarthquake locations along the southern Mid‐Atlantic Ridge have large uncertainties due to the sparse distribution of permanent seismological stations in and around the South Atlantic Ocean. Most of the earthquakes are associated with plate tectonic processes related to the formation of new oceanic lithosphere, as they are located close to the ridge axis or in the immediate vicinity of transform faults. A local seismological network of ocean‐bottom seismometers and land stations on and around the archipelago of Tristan da Cunha allowed for the first time a local earthquake survey for 1 year. We relate intraplate seismicity within the African oceanic plate segment north of the island partly to extensional stresses induced by a bordering large transform fault and to the existence of the Tristan mantle plume. The temporal propagation of earthquakes within the segment reflects the prevailing stress field. The strong extensional stresses in addition with the plume weaken the lithosphere and might hint at an incipient ridge jump. An apparently aseismic zone coincides with the proposed location of the Tristan conduit in the upper mantle southwest of the islands. The margins of this zone describe the transition between the ductile and the surrounding brittle regime. Moreover, we observe seismicity close to the islands of Tristan da Cunha and nearby seamounts, which we relate to ongoing tectono‐magmatic activity.

Investigation on critical crack-free cutting depth for single crystal silicon slicing with fixed abrasive wire saw based on the scratching machining experiments

The experimental research of single crystal silicon scratching machining is crucial for micro component machining, precision grinding and fixed abrasive wire saw precision slicing of single crystal silicon. The fixed abrasive wire saw slicing is the main slicing technology of large diameter single crystal silicon slicing process. During the fixed abrasive wire saw slicing process, the brittle material removal mode results in micro crack damage in wafer surface layer, which reduces the strength of sliced silicon wafer, and restricts silicon wafer thinner. The crack-free slicing surface could be obtained while the material is in ductile removal mode. In this study, the scratching machining experiments with the Nano Indenter and Berkovich diamond indenter scratching on single crystal silicon (100) plane along [010] orientation is conducted. The constant normal force 20mN, 100mN, and varied normal force from 0mN to 50mN are applied on the Berkovich indenter. The material removal mode is mainly in ductile regime while 20mN constant normal force, and the material removal mode is mainly in brittle regime and cleavage fracture emerge while 100mN constant normal force. The tangential friction force of scratching machining process changes from smooth to fluctuate when the varied normal force from 0mN to 50mN, and material removal mode from ductile regime to brittle regime. The critical normal force of ductile transition to brittle is 26mN. However, the scratching machining experimental results near the ductile regime removal mode show that the scratch exists obvious elastic recovery. The elastic recovery of scratch affects the material removal amount and machining accuracy. Based on the scratching machining experimental results, the critical crack-free cutting depth per abrasive for single crystal silicon slicing with fixed abrasive wire saw is analyzed. The results in this paper are useful for the single crystal silicon micro component machining and slicing process parameters selection of fixed abrasive wire saw.

Strain localization and elastic-plastic coupling during deformation of porous sandstone

Results of axisymmetric compression tests on weak, porous Castlegate Sandstone (Cretaceous, Utah, USA), covering a range of dilational and compactional behaviors, are examined for localization behavior. Assuming isotropy, bulk and shear moduli evolve as increasing functions of mean stress and Mises equivalent shear stress respectively, and as decreasing functions of work-conjugate plastic strains. Acoustic emissions events located during testing show onset of localization and permit calculation of observed shear and low-angle compaction localization zones, or bands, as localization commences. Total strain measured experimentally partitions into: A) elastic strain with constant moduli, B) elastic strain due to stress dependence of moduli, C) elastic strain due to moduli degradation with increasing plastic strain, and D) plastic strain. The third term is the elastic-plastic coupling strain, and though often ignored, contributes significantly to pre-failure total strain for brittle and transitional tests. Constitutive parameters and localization predictions derived from experiments are compared to theoretical predictions. In the brittle regime, predictions of band angles (angle between band normal and maximum compression) demonstrate good agreement with observed shear band angles. Compaction localization was observed in the transitional regime in between shear localization and spatially pervasive compaction, over a small range of mean stresses. In contrast with predictions, detailed acoustic emissions analyses in this regime show low angle, compaction-dominated but shear-enhanced, localization.

Mechanical behavior, failure mode, and transport properties in a porous carbonate

AbstractWe performed a systematic investigation of mechanical compaction, strain localization, and permeability in Leitha limestone. This carbonate from the area of Vienna (Austria) occurs with a broad range of grain sizes and porosity, due to changes in depositional regime and degree of cementation. Our new mechanical data revealed a simple relation between porosity and mechanical strength in both the brittle and ductile regimes. Increasing cementation and decreasing porosity led to a significant increase of the rock strength in both regimes. Micromechanical modeling showed that the dominant micromechanisms of inelastic deformation in Leitha limestone are pore‐emanated microcracking in the brittle regime, and grain crushing and cataclastic pore collapse in the ductile regime. Microstructural analysis and X‐ray computed tomography revealed the development of compaction bands in some of the less cemented samples, while more cemented end‐members failed by cataclastic flow in the compactant regime. In contrast to mechanical strength, permeability of Leitha limestone was not significantly impacted by increasing cementation and decreasing porosity. Our microstructural and tomography data showed that this was essentially due to the existence of a backbone of connected large macropores in all our samples, which also explained the relatively high permeability (in the range of 2–5 darcies) of Leitha limestone in comparison to other carbonates with significant proportion of micropores.

Experimental investigation on materials removal mechanism during grinding silicon carbide ceramics with single diamond grain

A single grain grinding experiment with fixed speed ratio vs/vw was designed to decouple the effect of grinding speed and undeformed chip thickness (UCT) on the SiC material removal mechanism during elevating the grinding wheel speed. Ground surface and subsurface topography, grinding forces, and specific energy were measured with grinding speed ranging from 20 to 160m/s and maximum UCT agmax from 0.02 to 3μm. The results demonstrated the grinding force and specific grinding energy show an evident decreased tendency with the increasing of grinding speed, despite the agmax value was kept at 0.03, 1μm. However, at agmax=0.3μm, the grinding force has a peak value with the increment of grinding wheel speed. The subsurface has the same trend. Based on the subsurface morphologies, grinding forces, grinding energy, the critical grinding wheel speeds vs=100, 80, 80m/s were determined at the agmax=0.03, 0.3, 1μm, respectively. Besides, grinding forces show different growth rates with the gradually increasing agmax at three stages under typical grinding speeds due to the transition of material removal mechanism. The critical agmax values for ductile-brittle transition and beginning of brittle regime grinding are determined as 0.3 and 1μm by surface and subsurface morphologies, grinding forces, grinding energy, respectively.

Experimental studies on mechanical properties and ductile‐to‐brittle transition of ice‐silica mixtures: Young's modulus, compressive strength, and fracture toughness

AbstractWe measured Young's modulus, fracture toughness, and compressive strength of ice and of ice‐0.25‐μm hard silica bead mixtures in controlled systematic experiments to determine the effect of silica on the ductile‐to‐brittle transition. Unconfined compressive strength was measured in a cold room at −10°C under a constant strain rate ranging from 10−5 to 6 × 10−1 s−1 of mixtures with silica volume fraction f of 0, 0.06, and 0.18. In the brittle regime, the compressive strength σpeak was a maximum at the transitional strain rate and then decreased with increasing strain rate. In the ductile regime, the σpeak increased exponentially with increasing strain rate as . The stress exponent n for f = 0.06 and 0.18 was ~6, twice as large as the value of pure ice, n ~ 3. The transitional strain rate increased with increasing silica volume fraction; 10−3–10−2 s−1 for pure ice, 10−2–10−1 s−1 for f = 0.06, and >6 × 10−1 s−1 for f = 0.18. Fracture toughness and Young's modulus were measured over the range 0 ≤ f ≤ 0.34. Fracture toughness scaled as f0.5, while Young's modulus increased linearly with f. Finally, a theoretical model of the transitional strain rate proposed by Schulson (1990) and Renshaw and Schulson (2001) was compared to the measured transitional strain rates. Model predictions were in accord with measured transitional strain rates for pure ice but somewhat higher than observed for ice‐silica mixtures. Large model uncertainty was due to high sensitivity of the transitional strain rate to the stress exponent n.