Non-recoverable Deformation Research Articles

Biomechanical Evaluation of Suture Augmentation of Dorsal Locking Plate Fixation in Transverse Patella Fractures.

Adjunctive suture augmentation of patellar plate fixation has yet to be investigated. Our biomechanical study sought to evaluate whether suture augmentation improves dorsal patellar locking plate fixation. Our hypothesis was that suture augmentation would improve fixation of this construct. A transverse patella fracture in six matched cadaveric pairs was stabilized using a patellar locking plate with or without suture augmentation. Specimens were tested at 60° knee flexion with load placed through quadriceps. Cyclic loading followed by load to failure was done. Stiffness, deformation at peak, and nonrecoverable deformation were calculated. During cyclic loading, suture augmentation demonstrated a higher average stiffness throughout all loads. At the final cycle, deformation was markedly higher without suture augmentation. Average load to failure was higher with suture augmentation. Maximum load to failure occurred at 2500 N in both groups. Suture augmentation in a transverse patellar fracture model improved dorsal plate fixation, leading to less fracture displacement at the final load. Although suture augmentation demonstrated higher stiffness and lower deformation, these trends were not statistically significant. In both groups, plate fixation sustained very high loads, which reflects the fixation strength of the dorsal locking plate and screw construct in this fracture model.

Biomechanical Comparison of FiberLock Suspensionplasty and Flexor Carpi Radialis Ligament Reconstruction for Treatment of Thumb Carpometacarpal Osteoarthritis.

The purpose of this study was to compare the cyclic and load to failure characteristics of post-trapeziectomy suspensionplasty with the FiberLock Suspension System (FLSS; Arthrex Inc., Naples, Florida) to flexor carpi radialis ligament reconstruction (FCRLR). We hypothesized that the FLSS will have increased stiffness, yield, and ultimate load compared with FCRLR. Ten matched pairs of cadaveric hands were used. One side of each pair was randomly assigned to receive the FCRLR or FLSS and the contralateral side received the other suspensionplasty. A complete trapeziectomy was performed followed by FLSS or FCRLR. Cyclic and load to failure characteristics were measured with loading in the distal to proximal direction. A preload of 1 N with 30 cycles of 1 N to 10 N was applied, followed by load to failure. A paired t test was used for statistical analysis (P < .05). The FLSS had significantly decreased nonrecoverable deformation and deformation at peak load during cyclic loading (P < .04). The FLSS also had significantly increased stiffness, yield load, ultimate load, and load and energy absorbed at 10 mm displacement compared with FCRLR (P < .04). All 10 FCRLR specimens failed with suture tearing through the tendon. Nine FLSS specimens failed due to suture slipping from the SwiveLock anchor (Arthrex Inc., Naples, Florida) and 1 failed due to the FiberTak anchor (Arthrex Inc., Naples, Florida) pulling through the index metacarpal. Suspensionplasty with the FLSS demonstrated greater structural integrity compared with FCRLR following trapeziectomy. The FLSS procedure may result in decreased thumb subsidence and decreased construct failure.

Analysis and design of RC unbonded PT shear walls in isolation and integrated into buildings: A state-of-the-art review

Shear walls play crucial roles in buildings located in the seismically active regions by efficiently mitigating the impact of seismic forces. However, they have drawbacks regarding their non-recoverable deformation and, thus, lack of reusability once damaged during an earthquake. One potential solution to this problem is the use of post-tensioned (PT) shear walls. These walls rock over the base during seismic events and regain their original position after the event, showing self-centering behaviour. The self-centering behaviour makes these walls reusable and reduces the downtime of the structure, thus making them a sustainable solution over conventional shear walls. Often, they are fitted with either internal or external energy dissipators to enhance the energy dissipation capacity. The present study aims at reviewing past analytical and numerical works, design methods, and international codes on reinforced concrete (RC) PT shear walls. The study also focuses on the models used in the past to investigate the behaviour of these walls. The parameters that affect the performance of RC PT shear walls are presented. Also, the global behaviour and the system interaction of RC PT shear walls integrated into buildings have been discussed. Finally, this paper presents the summary and critical observations, along with future recommendations on RC PT shear walls.

Determination of the Design Parameters of SMA Cables for Self-Centering Frame Structures

In order to improve the force performance of traditional anti-buckling energy dissipation bracing with excessive non-recoverable deformation caused by strong seismic action, this paper presents a prestress-braced frame structure system with shape memory alloy (SMA) and investigates its deformation characteristics under a horizontal load. Firstly, this paper establishes a theoretical analysis model by analyzing the geometric relationship between the deformation of SMA cables and inter-story displacement based on the internal force balance equation. The model is used to solve the anti-lateral displacement stiffness of the SMA cable-supported frame structure and to derive a reasonable formula for calculating the initial prestress and cross-sectional area of SMA cables. Then, the mechanical behavior of the SMA cable-supported frame structure system under an equivalent horizontal load is simulated using ABAQUS software and compared with the calculated results of conventional tie-supported and non-dissipative-supported frame structures. The results show that the force performance of the frame structure system determined by the SMA cable design method proposed in this paper is significantly improved under the horizontal load. Furthermore, it can ensure a certain ductility requirement of the frame structure system, which verifies the effectiveness of the design method of the SMA cable frame structure system proposed in this paper.

Biomechanical characteristics of a new looping stitch versus the classic Krackow stitch for distal biceps fixation

The purpose of this study was to quantify the biomechanical characteristics of a new looping stitch, developed with the concepts of a looping, locking stitch that decreases needle penetrations of the tendon, and compare it to a classic Krackow stitch for distal biceps suture-tendon fixation. The Krackow stitch with No. 2 braided suture and the looping stitch with a No. 2 braided suture loop attached to a 25-mm-length by 1.3-mm-width polyblend suture tape were compared. The Looping stitch was performed with single strand locking loops and wrapping suture around the tendon, resulting in half the needle penetrations through the graft compared to the Krackow stitch. Ten matched pairs of human distal biceps tendons were used. One side of each pair was randomly assigned to either the Krackow or the looping stitch, and the contralateral side was used for the other stitch. For biomechanical testing, each construct was preloaded to 5 N for 60 seconds, followed by cyclic loading to 20 N, 40 N, and 60 N for 10 cycles each, and then loaded to failure. The deformation of the suture-tendon construct, stiffness, yield load, and ultimate load were quantified. Comparisons between the Krackow and looping stitches were performed with a paired t-test using P<.05 as statistically significant. The Krackow stitch and looping stitch had no significant difference in stiffness, peak deformation, or nonrecoverable deformation after 10 cycles of loading to 20 N, 40 N, and 60 N. There was no difference between the Krackow stitch and looping stitch in load applied to displacement of 1 mm, 2 mm, and 3 mm. The ultimate load showed that the looping stitch was significantly stronger compared to the Krackow stitch (Krackow stitch: 223.7±50.3 N; looping stitch: 312.7±53.8 N) (P=.002). The failure modes were either suture breakage or tendon cut through. For the Krakow stitch, there was 1 suture breakage and 9 tendons cut through. For the looping stitch, there were five suture breakages, and five tendons cut through. With fewer needle penetrations, incorporation of 100% of the tendon diameter, and a higher ultimate load to failure compared to the Krackow stitch, the Looping stitch may be a viable option to reduce deformation, failure, and cut-out of the suture-tendon construct.

Quantifying physical and rheological properties of trichloroethylene-asphalt system to improve performance evaluation of recycled asphalt

In extracting the aged asphalt from field pavement via centrifugal extraction method, the trichloroethylene solvent tends to reside in the recycled asphalt, which can bias the property assessments of the recycled asphalt. This research evaluated the physical and rheological properties of the recycled asphalt that contained different masses of trichloroethylene, via fluorescence microscopy, Fourier transform infrared (FTIR) and dynamic shear rheology tests. Based on the test results, the effects of trichloroethylene on the properties of asphalt-trichloroethylene system were derived. It was found that the fluorescence microscope worked well for distinguishing the morphologies of trichloroethylene and asphalt in the trichloroethylene-asphalt system. A method was thus developed based on microscope image recognition to calculate the content of trichloroethylene in the asphalt. The FTIR results indicated that the interactions between the trichloroethylene and asphalt compositions generated two new absorption peaks in the infrared spectra, namely 562 cm−1 and 994 cm−1. The ratio of the above two peak areas (i.e., I994/I562) exhibited a two-stage linear varying trend with the trichloroethylene content, which provided references for predicting the trichloroethylene content in the asphalt using the infrared spectra. Trichloroethylene also influenced the rheological properties of recycled asphalt, including the shear modulus, phase angle, non-recoverable deformation and elastic recovery. As the trichloroethylene content rose, the shear modulus and elastic recovery of the trichloroethylene-asphalt system reduced, while the phase angle and non-recoverable deformation of the system increased. The above relationships between the trichloroethylene content and the properties of the asphalt-trichloroethylene system were expected to exclude the effect of the residual trichloroethylene on the asphalt properties, to improve the performance assessments of the recycled asphalt.

Effect of maleic anhydride grafted and gamma-irradiated waste polypropylene on rheological properties of asphalt binder

ABSTRACT Waste polymers have been employed as a modifier in bitumen to improve the performance of the binders and reduce plastic pollution. Grafting of maleic anhydride (MA) is a method to increase the chemical and physical consistency between the polymer and binder. In this study, maleic anhydride grafted waste polypropylene was employed as a bitumen modifier. Gamma irradiation is applied to waste polypropylene to improve the compatibility. The effects of MA-grafted irradiated waste polypropylene (PP-γ-MA) on physical and rheological properties of bitumen were investigated through a test program. Storage stability tests signifies that the gamma irradiation could diminish the phase separation between the modifier and bitumen. The thermorheological tests showed employing PP-γ-MA improves the high temperature performance, whilst it has a slightly adverse effect on low temperature performance of bitumen. The results of multiple stress creep recovery (MSCR) test indicate that PP-γ-MA reduces the non-recoverable deformation and enhanced elastic recovery of the material, whereas the linear amplitude sweep (LAS) test result signifies PP-γ-MA improved the fatigue life of asphalt by increasing fatigue damage resistance under different strain levels. The rheological test results emphasised on the usability of PP-γ-MA as a modifier in binders.

A thermodynamic-based large deformation viscoplastic constitutive relationship for asphalt concrete compaction

This research proposes a large deformation, time-dependent viscoplastic constitutive relationship to enhance the prediction of the compaction degree of asphalt concrete materials under laboratory and field conditions. A large-deformation thermodynamic-based framework is presented. The Helmholtz free energy and rate of energy dissipation functions were assumed to derive rate-dependent constitutive relationships to relate multi-axial state of stresses to the recoverable and non-recoverable deformation response of asphalt concrete during compaction. A straightforward method that allows the calibration of the proposed model against laboratory compaction data (e.g., data from Superpave Gyratory Compactor; SGC) is presented. Numerical algorithms associated with the proposed constitutive relationship were implemented in the finite element (FE) code Abaqus via the user material subroutine UMAT. The model is calibrated against SGC deformation data at different number of gyrations (time). The calibrated model was utilized to predict the field compaction of asphalt concrete. Comparisons of the model predictions and field measurements showed that the model is capable of predicting the compaction of asphalt concrete materials both in the laboratory and in the field.

Prediction of Time to Soil Failure Based on Creep Strength Reduction Approach

Soils experience the unrecoverable, continuous deformation known as creep when they are subjected to a stage of constant deviator stress. Creep deformation is due to extrusion of adsorbed water in clay particles, causing the non-recoverable deformation and eventually reduction in the soil shear strength. This study aims to develop a method to determine the creep strength reduction behaviour of soils and prediction of time to occurrence of the creep failure. Case studies on clayey soils including halloysite-rich soil and smectite-rich soil were chosen. A series of triaxial creep tests were conducted in order to obtain the necessary experimental data. Based on the results, the ultimate long-term creep strength or critical stress level of halloysite-rich soil and smectite-rich soil was 85 and 55% of the soil peak strength, respectively. The ultimate time of creep strength reduction in halloysite-rich soil and smectite-rich soil was 10.34 and 46.08 years, respectively. The maximum creep strength reduction ratio of halloysite-rich soil and smectite-rich soil was 0.2 and 0.45, respectively. The developed method allowed predicting time to creep failure of soil specimens.

Investigation of Rheological Properties of Blended Cement Pastes Using Rotational Viscometer and Dynamic Shear Rheometer

To successfully process concrete, it is necessary to predict and control its flow behavior. However, the workability of concrete is not completely measured or specified by current standard tests. Furthermore, it is only with a clear picture of cement hydration and setting that full prediction and control of concrete performance can be generalized. In order to investigate the rheological properties of blended cement pastes, a rotational viscometer (RV) was used to determine the flow characteristics of ordinary and blended pastes to provide assurance that it can be pumped and handled. Additionally, a dynamic shear rheometer (DSR) was used to characterize both the viscous and elastic components of pastes. Ordinary Portland cement paste and blended pastes (slag, fly ash, and silica fume) were investigated in this study. The stress and strain of the blended specimens were measured by the DSR, which characterizes both viscous and elastic behaviors by measuring the complex shear modulus (the ratio of total shear stress to total shear strain) and phase angle (an indicator of the relative amounts of recoverable and nonrecoverable deformation) of materials. Cement pastes generally exhibit different rheological behaviors with respect to age, mineral admixture type, and cement replacement level.

Thermo-Responsive Shape-Memory Effect and Surface Features in Polycarbonate (PC)

The influence of programming strain and temperature on the shape memory effect and surface morphology in programmed polycarbonate (PC) samples via uni-axial stretching is investigated. It is found that the samples programmed at around the glass transition start temperature not only have micro-cracks on their surface, but also show a necking phenomenon. Furthermore, the surface of the necked area is concave, but the surface of the non-necked area is convex. On the other hand, despite the samples programmed at high temperatures being able to deform in a uniform manner at macroscopic scale, their surfaces are still uneven, either concave or convex. While the samples programmed at low temperatures are able to achieve full shape recovery, stretching at higher temperatures over the glass transition range to a higher strain may result in non-recoverable deformation.

Modeling the response of exogenously crosslinked tissue to cyclic loading: The effects of permanent set.

Bioprosthetic heart valves (BHVs), fabricated from exogenously crosslinked collagenous tissues, remain the most popular heart valve replacement design. However, the life span of BHVs remains limited to 10-15 years, in part because the mechanisms that underlie BHV failure remain poorly understood. Experimental evidence indicates that BHVs undergo significant changes in geometry with in vivo operation, which lead to stress concentrations that can have significant impact on structural damage. These changes do not appear to be due to plastic deformation, as the leaflets only deform in the elastic regime. Moreover, structural damage was not detected by the 65 million cycle time point. Instead, we found that this nonrecoverable deformation is similar to the permanent set effect observed in elastomers, which allows the reference configuration of the material to evolve over time. We hypothesize that the scission-healing reaction of glutaraldehyde is the underlying mechanism responsible for permanent set in exogenously crosslinked soft tissues. The continuous scission-healing process of glutaraldehyde allows a portion of the exogenously crosslinked matrix, which is considered to be the non-fibrous part of the extra-cellular matrix, to be re-crosslinked in the loaded state. Thus, this mechanism for permanent set can be used to explain the time evolving mechanical response and geometry of BHVs in the early stage. To model the permanent set effect, we assume that the exogenously crosslinked matrix undergoes changes in reference configurations over time. The changes in the collagen fiber architecture due to dimensional changes allow us to predict subsequent changes in mechanical response. Results show that permanent set alone can explain and, more importantly, predict how the mechanical response of the biomaterial change with time. Furthermore, we found is no difference in permanent set rate constants between the strain controlled and the stress controlled cyclic loading studies. An important finding we have is that the collagen fiber architecture has a limiting effect on the maximum changes in geometry that the permanent set effect can induce. This is due to the recruitment of collagen fibers as the changes in geometry due to permanent set increase. This means we can potentially optimize the BHV geometry based on the predicted the final BHV geometry after permanent set has largely ceased. Thus, we have developed the first structural constitutive model for the permanent set effect in exogenously crosslinked soft tissue, which can help to simulate BHV designs and reduce changes in BHV geometry during cyclic loading and thus potentially increasing BHV durability.

Rheological properties and anti-aging performance of asphalt binder modified with wood lignin

This study evaluated the potential use of wood lignin as partial substitute and performance modifier in asphalt binder. The rolling thin film oven (RTFO) and pressure aging vessel (PAV) methods were performed on asphalt samples to simulate different aging conditions. The Rotational Viscosity (RV), Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) tests were utilized to explore the influence of adding lignin on the rheological properties of asphalt binder. The Fourier Transform Infrared Spectroscopy (FTIR) was used to evaluate the anti-aging performance of lignin on asphalt binder. The rutting resistance of lignin modified asphalt binder at the high temperature was evaluated using Multi Stress Creep and Recovery (MSCR) test, while the fatigue life of asphalt binder was characterized using Linear Amplitude Sweep (LAS) test. The viscosity test results showed that the addition of wood lignin into asphalt binder caused stiffening effect. The DSR and BBR test results implied that adding lignin positively affected high-temperature rutting performance without adversely influencing low-temperature. The MSCR results indicated that the lignin improved the elastic recovery and reduced non-recoverable deformation of asphalt binder. The FTIR results indicates that the presence of lignin can help resist the formation of carbonyl structure in the aging process, and thus improved aging resistance of asphalt binder. The LAS test results showed that fatigue resistance of asphalt was negatively affected by lignin. The study results suggest that wood lignin is a promising modifier for asphalt materials with economic savings and environmental benefits.

Separation of drying strains and the calculation of drying stresses considering the viscoelasticity of red pine wood during drying

ABSTRACTThe objective of this study was to separate drying strains into elastic, viscoelastic, and viscous strains using free shrinkage and recovery from the deformation of slices at stress relief. The apparent shrinkage deformation was obtained by measuring the change in width of drying specimens during drying. Using the slice method, elastic and viscoelastic deformation were defined as the instantaneous change in width of a slice right after cutting and the change in the width of a slice with constant moisture content during 48 h, respectively. Viscous deformation, permanent and nonrecoverable deformation of wood, was defined as the difference in deformation between free shrinkage and the sum of the apparent, elastic, and viscoelastic deformations. These elastic, viscoelastic, and viscous strains were applied to a viscoelastic model, and coefficients of viscoelasticity and viscosity were derived. The drying stress and deformation of red pine wood at specific times during the drying process can be predicted using each coefficients and modulus of elasticity obtained by experiment.

Increased risk of muscle tears below physiological temperature ranges.

ObjectivesTemperature is known to influence muscle physiology, with the velocity of shortening, relaxation and propagation all increasing with temperature. Scant data are available, however, regarding thermal influences on energy required to induce muscle damage.MethodsGastrocnemius and soleus muscles were harvested from 36 male rat limbs and exposed to increasing impact energy in a mechanical test rig. Muscle temperature was varied in 5°C increments, from 17°C to 42°C (to encompass the in vivo range). The energy causing non-recoverable deformation was recorded for each temperature. A measure of tissue elasticity was determined via accelerometer data, smoothed by low-pass fifth order Butterworth filter (10 kHz). Data were analysed using one-way analysis of variance (ANOVA) and significance was accepted at p = 0.05.ResultsThe energy required to induce muscle failure was significantly lower at muscle temperatures of 17°C to 32°C compared with muscle at core temperature, i.e., 37°C (p < 0.01). During low-energy impacts there were no differences in muscle elasticity between cold and warm muscles (p = 0.18). Differences in elasticity were, however, seen at higher impact energies (p < 0.02).ConclusionOur findings are of particular clinical relevance, as when muscle temperature drops below 32°C, less energy is required to cause muscle tears. Muscle temperatures of 32°C are reported in ambient conditions, suggesting that it would be beneficial, particularly in colder environments, to ensure that peripheral muscle temperature is raised close to core levels prior to high-velocity exercise. Thus, this work stresses the importance of not only ensuring that the muscle groups are well stretched, but also that all muscle groups are warmed to core temperature in pre-exercise routines.Cite this article: Professor A. H. R. W. Simpson. Increased risk of muscle tears below physiological temperature ranges. Bone Joint Res 2016;5:61–65. DOI: 10.1302/2046-3758.52.2000484.

The Influence of Constructional Parameters on Deformability of Elastic Cotton Fabrics

This research is focused on the influence of constructional parameters such as the type of weave and density on deformability of pure cotton and cotton/elastane fabrics. In the research, two basic weaves were used: the plain and twill weave without (pure cotton) and with 6.2 percent of elastane in the weft direction. The density of the warp yarns was before bleaching 22yarns/cm and after end treatment (bleaching) from 24 to 31 yarns/cm. The chosen densities in the weft direction were 17 and 20 yarns/cm. The fabrics were cyclically loaded with maximum load 17.66 N. The non-recoverable deformation was measured after 30 seconds of relaxation after the fourth cycle of loading, according to ASTM D 3107–75. The research results show that elastane incorporation significantly decreased the non-recoverable deformation after loading. In the case of the twill weave, the decrease of non-recoverable deformation was from around 20% – twill without elastane to around 5% – twill with elastane – fabrics 7B and 8B. The non-recoverable deformation level decrease with fabrics in plain weave was also significant (from around 24% – plain without elastane to around 12% – plain with elastane). From the results of non-recoverable deformation, it is clearly seen that the chosen type of weave, plain and twill, significantly influenced the non-recoverable deformation level. The increase of density in the weft direction from 17 yarns/cm to 20 yarns/cm for pure cotton and cotton/elastane fabrics insignificantly influenced the non-recoverable deformation level. This means that the density increase of 3 yarns/cm is too low to significantly influence the deformability of pure cotton and cotton/elastane fabrics.

A Super Energy Mitigation Nanostructure at High Impact Speed Based on Buckyball System

The energy mitigation properties of buckyballs are investigated using molecular dynamics (MD) simulations. A one dimensional buckyball long chain is employed as a unit cell of granular fullerene particles. Two types of buckyballs i.e. C60 and C720 with recoverable and non-recoverable behaviors are chosen respectively. For C60 whose deformation is relatively small, a dissipative contact model is proposed. Over 90% of the total impact energy is proven to be mitigated through interfacial reflection of wave propagation, the van der Waals interaction, covalent potential energy and atomistic kinetic energy evidenced by the decent force attenuation and elongation of transmitted impact. Further, the C720 system is found to outperform its C60 counterpart and is able to mitigate over 99% of the total kinetic energy by using a much shorter chain thanks to its non-recoverable deformation which enhances the four energy dissipation terms. Systematic studies are carried out to elucidate the effects of impactor speed and mass, as well as buckyball size and number on the system energy mitigation performance. This one dimensional buckyball system is especially helpful to deal with the impactor of high impact speed but small mass. The results may shed some lights on the research of high-efficiency energy mitigation material selections and structure designs.

Energy absorption ability of buckyball C720 at low impact speed: a numerical study based on molecular dynamics

The dynamic impact response of giant buckyball C720 is investigated by using molecular dynamics simulations. The non-recoverable deformation of C720 makes it an ideal candidate for high-performance energy absorption. Firstly, mechanical behaviors under dynamic impact and low-speed crushing are simulated and modeled, which clarifies the buckling-related energy absorption mechanism. One-dimensional C720 arrays (both vertical and horizontal alignments) are studied at various impact speeds, which show that the energy absorption ability is dominated by the impact energy per buckyball and less sensitive to the number and arrangement direction of buckyballs. Three-dimensional stacking of buckyballs in simple cubic, body-centered cubic, hexagonal, and face-centered cubic forms are investigated. Stacking form with higher occupation density yields higher energy absorption. The present study may shed lights on employing C720 assembly as an advanced energy absorption system against low-speed impacts.

Structure and Mechanical Behavior of Elastomeric Multiblock Terpolymers Containing Glassy, Rubbery, and Semicrystalline Blocks

Multiblock copolymers containing glassy poly-(cyclohexylethylene) (C), rubbery poly(ethylene-alt-propylene) (P), and semicrystalline poly(ethylene) (E) were synthesized by sequential anionic polymerization of styrene, isoprene, and buta-diene followed by catalytic hydrogenation. The resulting CECP-CEC (denoted XPX) and CECP (XP) multiblock copolymers each contain 50 vol % of P and equal amounts of C and E. These materials have been studied by dynamic mechanical spectroscopy (DMS), transmission electron microscopy (TEM), small- an wide-angle X-ray scattering (SAXS and WAXS), di!erential scanning calorimetry (DSC), and tensile deformation to characterize the morphology, phase behavior, and mechanical properties. Microphase separation in these compounds is induced by crystallization of Eand/or chemical incompatibility between the three blocks, leading to a new type of morphology which contains continuous region of P and continuous region ofmicrophase-separated X, resulting inmechanically resilientmaterials.Highmolecular weight block copolymers microphase separate with two di!erent length scales associated with segregation between C and E and X and P. These structural features produce a nonclassical scaling relationship for the C!E domain spacing, d ! N0.31, where N is the degree of polymerization of CEC portion. The role of semicrystalline E domains during uniaxial deformation has been exposed withWAXS experiments, which support a two-stepmechanisminvolving recoverable and nonrecoverable deformation to di!erent extents.more » Strain hardening is observed in double-anchored XPX, but not in single-anchored XP, at large tensile strains.« less

Nanoindentation Behavior of Muscovite Subjected to Repeated Loading

A series of repeated loading nanoindentation experiments were performed on muscovite with a sharp indenter tip and loading direction normal to the basal plane, and the maximum load (Fmax⁡) was varied between 0.05 and 2.0 mN to examine the influences of load level on the modes of nanoscale deformation and the resulting estimation of hardness and elastic modulus. A critical maximum load, (Fmax⁡)crit, of about 0.25–0.5 mN marks the material’s completely different responses to repeated loading. If Fmax⁡<(Fmax⁡)crit, fully closed, completely reversible loading-unloading (L/U) hysteresis loops were observed with characteristic smooth, nonlinear curves, which can be attributed to the formation and annihilation of incipient kink bands. If Fmax⁡>(Fmax⁡)crit, dispersed L/U loops characterized by nonrecoverable deformation and randomly occurring pop-ins in the loading section of the loops were observed; moreover, it appears that pop-ins are the major cause for the dispersion of the L/U loops. For the latter case, after a few L/U cycles, pop-ins tend to disappear, and the L/U loops start to merge together, resulting in the shakedown of the repeated loading. A comparison of the unloading section of the loops indicates that the contact stiffness increases with the number of L/U cycles, or the mineral exhibits cyclic hardening behavior. The resulting influences on the hardness and elastic modulus are evaluated against those obtained by monotonic loading and further discussed in accordance with indentation size effects and underlying nanoscale deformation mechanisms at different load levels.