Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
163,629
result(s) for
"strains"
Sort by:
Does the Spraino low-friction shoe patch prevent lateral ankle sprain injury in indoor sports? A pilot randomised controlled trial with 510 participants with previous ankle injuries
BackgroundLateral ankle sprains are common in indoor sports. High shoe–surface friction is considered a risk factor for non-contact lateral ankle sprains. Spraino is a novel low-friction patch that can be attached to the outside of sports shoes to minimise friction at the lateral edge, which could mitigate the risk of such injury. We aimed to determine preliminary effectiveness (incidence rate and severity) and safety (harms) of Spraino to prevent lateral ankle sprains among indoor sport athletes.MethodsIn this exploratory, parallel-group, two-arm pilot randomised controlled trial, 510 subelite indoor sport athletes with a previous lateral ankle sprain were randomly allocated (1:1) to Spraino or ‘do-as-usual’. Allocation was concealed and the trial was outcome assessor blinded. Match and training exposure, number of injuries and associated time loss were captured weekly via text messages. Information on harms, fear-of-injury and ankle pain was also documented.Results480 participants completed the trial. They reported a total of 151 lateral ankle sprains, of which 96 were categorised as non-contact, and 50 as severe. All outcomes favoured Spraino with incidence rate ratios of 0.87 (95% CI 0.62 to 1.23) for all lateral ankle sprains; 0.64 (95% CI 0.42 to 0.98) for non-contact lateral ankle sprains; and 0.47 (95% CI 0.25 to 0.88) for severe lateral ankle sprains. Time loss per injury was also lower in the Spraino group (1.8 vs 2.8 weeks, p=0.014). Six participants reported minor harms because of Spraino.ConclusionCompared with usual care, athletes allocated to Spraino had a lower risk of lateral ankle sprains and less time loss, with only few reported minor harms.Trial registration number NCT03311490.
Journal Article
Strain Rate Effect of Siltstone Under Triaxial Compression and Its Interpretation from Damage Mechanics
Four groups (1 × 10–5/s, 1 × 10–4/s, 1 × 10–3/s and 1 × 10–2/s) of triaxial compression tests at a confining pressure of 30 MPa are carried out to clarify the strain rate effect and damage evolution of siltstone. The elastic modulus, peak stress, strain energy evolution and failure modes of siltstone at different strain rates are analyzed, followed by an interpretation based on statistical damage theory. In the range of the quasi-static strain rate, as the strain rate increases, the elastic modulus, peak stress, total strain energy density and elastic strain energy density at the peak stress of siltstone increase, and the failure mode of the siltstone gradually change from single-plane shear failure to extensile failure. The plastic shear strain is adopted as the random variable of the Weibull distribution to formulate a new statistical damage model, which can better reproduce the post-peak characteristics of the stress–strain curve and interpret the damage evolution process of siltstone; this also reveals that the nonlinear evolution of random variables with axial strain should be considered to capture the post-peak stress–strain curve. The damage variable evolution curves are similar to the dissipated strain energy density curves, which are ‘L-shaped’. Finally, a simplified method for determining the influence of strain rate on damage at peak stress Dcr is proposed and discussed.HighlightsIn the range of the quasi-static strain rate, four groups of triaxial compression tests are carried out to reveal the strain rate effect of siltstone.Incorporating the plastic shear strain, a statistical damage model is proposed to better interpret the mechanical behaviour of siltstone.Based on the damage theory, a simplified method for determining the influence of strain rate on damage at peak stress Dcr is proposed.
Journal Article
Earthquake and volcano deformation
Earthquake and Volcano Deformationis the first textbook to present the mechanical models of earthquake and volcanic processes, emphasizing earth-surface deformations that can be compared with observations from Global Positioning System (GPS) receivers, Interferometric Radar (InSAR), and borehole strain- and tiltmeters. Paul Segall provides the physical and mathematical fundamentals for the models used to interpret deformation measurements near active faults and volcanic centers.
Segall highlights analytical methods of continuum mechanics applied to problems of active crustal deformation. Topics include elastic dislocation theory in homogeneous and layered half-spaces, crack models of faults and planar intrusions, elastic fields due to pressurized spherical and ellipsoidal magma chambers, time-dependent deformation resulting from faulting in an elastic layer overlying a viscoelastic half-space and related earthquake cycle models, poroelastic effects due to faulting and magma chamber inflation in a fluid-saturated crust, and the effects of gravity on deformation. He also explains changes in the gravitational field due to faulting and magmatic intrusion, effects of irregular surface topography and earth curvature, and modern concepts in rate- and state-dependent fault friction. This textbook presents sample calculations and compares model predictions against field data from seismic and volcanic settings from around the world.
Earthquake and Volcano Deformationrequires working knowledge of stress and strain, and advanced calculus. It is appropriate for advanced undergraduates and graduate students in geophysics, geology, and engineering.
Professors: A supplementary Instructor's Manual is available for this book. It is restricted to teachers using the text in courses. For information on how to obtain a copy, refer to: http://press.princeton.edu/class_use/solutions.html
eBook
Post-peak Stress–Strain Curves of Brittle Rocks Under Axial- and Lateral-Strain-Controlled Loadings
To systematically study the influence of axial- and lateral-strain-controlled loadings on the strength and post-peak deformation behaviors of brittle rocks, four types of rocks (marble, sandstone, granite, and basalt) are tested under uniaxial and triaxial compressions, using a brittle hard rock testing system named Stiffman with high loading system stiffness. The test results show that the post-peak stress–strain curves of rock specimens under axial-strain-controlled loading are Class I, while those under lateral-strain-controlled loading are mostly Class II when the confining pressure is low. As confining pressure increases, the stress–strain curves change to Class I. Compared with that under lateral-strain-controlled loading, the failure of rock under axial-strain-controlled loading is more intense, the peak strength is higher, and the residual strength is lower. It is demonstrated that Class II post-peak stress–strain curves obtained by lateral-strain-controlled loading are caused by the unloading of the actuator in response to the servo-control system to keep the lateral strain rate constant. In the post-peak deformation stage, large dilation occurs, which leads to a sudden increase of the lateral strain rate; in order to keep the lateral strain rate at the set value under lateral-strain-controlled loading, the servo-control system must force the actuator to unload. When rock dilation occurs in the pre-peak deformation stage, unloading can occur before the peak strength, resulting in a decrease of peak strength compared with the peak strength obtained by axial-strain-controlled loading. It is found that the more brittle and dilatant a rock, the earlier the unloading of the actuator is, and the larger the peak strength decreases and the more obvious the Class II curve is.
Journal Article
Strain rate- and temperature-dependent mechanical properties of Ti-6Al-4V in dynamic compression: hardening and softening behaviour analysis using strain energy-based method
Studies have shown that the deformation of Ti alloys is due to the competition between hardening and softening effects under dynamic loading. However, there are limited indicators of this behaviour throughout the complete stress–strain process. This study aims to quantify the impact of strain rate and temperature on the hardening/softening behaviour of Ti-6Al-4V using a split-Hopkinson pressure bar system over a range of 2000 to 7000 s
−1
strain rates and temperatures from 25 to 800°C. Firstly, this study proposes an evaluation index of material hardening/softening behaviour based on the complete stress–strain curve and energy evolution characteristic. Further, the dynamic mechanical properties of Ti-6Al-4V are investigated through the analysis of the stress–strain relationship and fracture morphology. Finally, the hardening/softening index is calculated and analysed. The findings revealed that the fracture surface of the impact specimen displayed dimple-like and smooth features, that are significantly influenced by both temperature and strain rate. The stress–strain curves demonstrated that Ti-6Al-4V exhibits remarkable strain-rate strengthening, plastic increasing, and strain work hardening behaviour. The hardening/softening index
B
r
decreases with an increase in strain rate. For specific strain rates of 3000, 5000 and 7000 s
−1
,
B
r
increases as the loading temperature rises from 25 to 400°C, but decreases when the loading temperature is increased to 600°C. At a strain rate of 2000 s
−1
,
B
r
increases monotonically until the loading temperature reaches
∼
800°C. These observations are found to be related to the microstructural evolution at varying temperatures and strain rates.
Graphic Abstract
Journal Article
Cracking and Stress–Strain Behavior of Rock-Like Material Containing Two Flaws Under Uniaxial Compression
This paper investigates the cracking and stress–strain behavior, especially the local strain concentration near the flaw tips, of rock-like material containing two flaws. A series of uniaxial compression tests were carried out on rock-like specimens containing two flaws, with strain gauges mounted near the flaw tips to measure the local strain concentration under the uniaxial compressive loading. Four different types of cracks (wing cracks, anti-wing cracks, coplanar shear cracks and oblique shear cracks) and seven patterns of crack coalescences (T1 and T2; S1 and S2; and TS1, TS2 and TS3) are observed in the experiments. The type of crack coalescence is related to the geometry of the flaws. In general, the crack coalescence varies from the S-mode to the TS-mode and then to the T-mode with the increase of the rock bridge ligament angle. The stress–strain curves of the specimens containing two flaws are closely related to the crack development and coalescence process. The strain measurements indicate that the local tensile strain concentration below or above the pre-existing flaw tip causes wing or anti-wing cracks, while the local compressive strain concentration near the flaw tip is related to the shear crack. The measured local tensile strain shows a jump at the initiation of wing- and anti-wing cracks, reflecting the instant opening of the wing- and anti-wing crack propagating through the strain gauge. During the propagation of wing- and anti-wing cracks, the measured local tensile strain gradually increases with few jumps, implying that the opening deformation of wing- and anti-wing cracks occurs in a stable manner. The shear cracks initiate followed by a large and abrupt compressive strain jump and then quickly propagate in an unstable manner resulting in the failure of specimens.
Journal Article
Uniting tensile ductility with ultrahigh strength via composition undulation
Metals with nanocrystalline grains have ultrahigh strengths approaching two gigapascals. However, such extreme grain-boundary strengthening results in the loss of almost all tensile ductility, even when the metal has a face-centred-cubic structure—the most ductile of all crystal structures
1
–
3
. Here we demonstrate that nanocrystalline nickel–cobalt solid solutions, although still a face-centred-cubic single phase, show tensile strengths of about 2.3 gigapascals with a respectable ductility of about 16 per cent elongation to failure. This unusual combination of tensile strength and ductility is achieved by compositional undulation in a highly concentrated solid solution. The undulation renders the stacking fault energy and the lattice strains spatially varying over length scales in the range of one to ten nanometres, such that the motion of dislocations is thus significantly affected. The motion of dislocations becomes sluggish, promoting their interaction, interlocking and accumulation, despite the severely limited space inside the nanocrystalline grains. As a result, the flow stress is increased, and the dislocation storage is promoted at the same time, which increases the strain hardening and hence the ductility. Meanwhile, the segment detrapping along the dislocation line entails a small activation volume and hence an increased strain-rate sensitivity, which also stabilizes the tensile flow. As such, an undulating landscape resisting dislocation propagation provides a strengthening mechanism that preserves tensile ductility at high flow stresses.
A nanocrystalline metallic alloy with ultrahigh tensile strength and good ductility is achieved by introducing compositional undulation in a highly concentrated solid solution.
Journal Article
A Review of Dynamic Experimental Techniques and Mechanical Behaviour of Rock Materials
The purpose of this review is to discuss the development and the state of the art in dynamic testing techniques and dynamic mechanical behaviour of rock materials. The review begins by briefly introducing the history of rock dynamics and explaining the significance of studying these issues. Loading techniques commonly used for both intermediate and high strain rate tests and measurement techniques for dynamic stress and deformation are critically assessed in Sects.
2
and
3
. In Sect.
4
, methods of dynamic testing and estimation to obtain stress–strain curves at high strain rate are summarized, followed by an in-depth description of various dynamic mechanical properties (e.g. uniaxial and triaxial compressive strength, tensile strength, shear strength and fracture toughness) and corresponding fracture behaviour. Some influencing rock structural features (i.e. microstructure, size and shape) and testing conditions (i.e. confining pressure, temperature and water saturation) are considered, ending with some popular semi-empirical rate-dependent equations for the enhancement of dynamic mechanical properties. Section
5
discusses physical mechanisms of strain rate effects. Section
6
describes phenomenological and mechanically based rate-dependent constitutive models established from the knowledge of the stress–strain behaviour and physical mechanisms. Section
7
presents dynamic fracture criteria for quasi-brittle materials. Finally, a brief summary and some aspects of prospective research are presented.
Journal Article