scholarly journals Damage evaluation and precursor of sandstone under the uniaxial compression: Insights from the strain-field heterogeneity

PLoS ONE ◽  
2021 ◽  
Vol 16 (12) ◽  
pp. e0262054
Author(s):  
Hongming Cheng ◽  
Xiaobin Yang ◽  
Zewen Zhang ◽  
Wenlong Li ◽  
Zhangxuan Ning
Keyword(s):  
Strain Field ◽  
Compressive Load ◽  
Image Correlation ◽  
High Rate ◽  
Damage State ◽  
Drastic Increase ◽  
Field Heterogeneity ◽  
Physical Changes ◽  
Quantitative Indicators ◽  
Rock Specimens

The stress-induced microcrack evolution in rock specimens causes a series of physical changes and heterogeneous deformations. Some of these attributes (such as sound, electricity, heat, etc.) have been effectively used to identify the damage state and precursory information of the rock specimens. However, the strain-field heterogeneity has not been investigated previously. In this study, the relationship of the strain-field heterogeneity and damage evolution of three sandstone specimens under the uniaxial compressive load was analyzed statistically. The acoustic emission (AE) and two-dimensional digital image correlation were employed for real-time evaluation of the AE parameters and strain-field heterogeneity. The results showed that the strain-field heterogeneity was closely related to the rock damage that amplified with the applied stress, and exhibited two features; numerical difference and spatial concentration. Subsequently, these two features were characterized by the two proposed heterogeneous quantitative indicators (i.e., the degree and space heterogeneities). Further, their four transition processes were in agreement with the damage stages confirmed by AE parameters: a relatively constant trend; growth with a relatively constant rate; drastic increase trend; and increase with a high rate to maximum value. Moreover, a time sequence chain for damage precursor was built, where the heterogeneous quantitative indicators and AE parameters differed in sensitivity to microcrack development and can be used as a damage warning at the varying magnitude of the external load.

Methodology for in situ stress intensity factor determination on cracked structures by digital image correlation

2010 ◽  
Vol 1 (4) ◽  
pp. 344-357 ◽  
Author(s):  
V. Richter‐Trummer ◽  
P.M.G.P. Moreira ◽  
S.D. Pastrama ◽  
M.A.P. Vaz ◽  
P.M.S.T. de Castro
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Digital Image Correlation ◽  
Intensity Factor ◽  
Digital Image ◽  
Strain Field ◽  
Image Correlation ◽  
Content Type ◽  
Cracked Structures

PurposeThe purpose of this paper is to develop a methodology for in situ stress intensity factor (SIF) determination that can be used for the analysis of cracked structures. The technique is based on digital image correlation (DIC) combined with an overdetermined algorithm.Design/methodology/approachThe linear overdeterministic algorithm for calculating the SIF based on stress values around the crack tip is applied to a strain field obtained by DIC.FindingsAs long as the image quality is sufficiently high, a good accuracy can be obtained for the measured SIF. The crack tip can be automatically detected based on the same strain field. The use of the strain field instead of the displacement field, eliminates problems related to the rigid body motion of the analysed structure.Practical implicationsIn future works, based on the applied techniques, the SIF of complex cracked plane stress structures can be accurately determined in real engineering applications.Originality/valueThe paper demonstrates application of known techniques, refined for other applications, also the use of stress field for SIF overdeterministic calculations.

scholarly journals A new methodology to identify minimum strain anatomical lines based on 3-D digital image correlation

2017 ◽  
Vol 8 (2) ◽  
pp. 337-347 ◽  
Author(s):  
Jorge Barrios-Muriel ◽  
Francisco Javier Alonso Sánchez ◽  
David Rodríguez Salgado ◽  
Francisco Romero-Sánchez
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Strain Field ◽  
Three Dimensional ◽  
Wearable Devices ◽  
Plane Motion ◽  
Human Motion ◽  
The Body ◽  
Image Correlation ◽  
Minimum Deformation

Abstract. Today there is continuous development of wearable devices in various fields such as sportswear, orthotics and personal gadgets, among others. The design of these devices involves the human body as a support environment. Based on this premise, the development of wearable devices requires an improved understanding of the skin strain field of the body segment during human motion. This paper presents a methodology based on a three dimensional digital image correlation (3D-DIC) system to measure the skin strain field and to estimate anatomical lines with minimum deformation as design criteria for the aforementioned wearable devices. The errors of displacement and strain measurement related to 3-D reconstruction and out-of-plane motion are investigated and the results are acceptable in the case of large deformation. This approach can be an effective tool to improve the design of wearable devices in the clinical orthopaedics and ergonomics fields, where comfort plays a key role in supporting the rehabilitation process.

scholarly journals Strain rate and thermal softening effects in shear testing of AA7075-T6 sheet

2018 ◽  
Vol 183 ◽  
pp. 02037 ◽  
Author(s):  
Taamjeed Rahmaan ◽  
Ping Zhou ◽  
Cliff Butcher ◽  
Michael J. Worswick
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Rate Sensitivity ◽  
Thermal Conditions ◽  
Shear Loading ◽  
Image Correlation ◽  
High Rate ◽  
Strain Rates ◽  
Shear Testing ◽  
Plane Shear

Shear tests were performed at strain rates ranging from quasi-static (0.01 s-1) to 500 s-1 for AA7075-T6 sheet metal alloy at room temperature. A miniature sized shear specimen was used in this work to perform high strain rate shear testing. Digital image correlation (DIC) techniques were employed to measure the strains in the experiments. At maximum in-plane shear strains greater than 20%, the AA7075-T6 alloy demonstrated a reduced work hardening rate at elevated strain rates. At lower strains, the AA7075-T6 alloy showed mild positive rate sensitivity. The strain to localization (using the Zener-Holloman criterion), measured using the DIC technique, decreased with strain rate in shear loading. The strain at complete failure, however, exhibited an increase at the highest strain rate (500 s-1). The current work also focused on characterization of the thermal conditions occurring during high rate loading in shear with in situ high speed thermal imaging. Experimental results from the highest strain rate (500 s-1) tests showed a notable increase in temperature within the specimen gauge region as a result of the conversion of plastic deformation energy into heat.

STRAIN RATE-DEPENDENT CHARACTERIZATION OF THE IN-PLANE SHEAR RESPONSE OF A UNIDIRECTIONAL NON-CRIMP FABRIC CARBON FIBER/SNAP-CURE EPOXY COMPOSITE

2021 ◽  
Author(s):  
KHIZAR ROUF ◽  
MICHAEL J. WORSWICK ◽  
JOHN MONTESANO
Keyword(s):  
Carbon Fiber ◽  
Strain Rate ◽  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Equilibrium ◽  
Epoxy Composite ◽  
Axial Strain ◽  
Image Correlation ◽  
High Rate ◽  
Plane Shear

The dynamic in-plane shear stress-strain response of a unidirectional non- crimp fabric carbon fiber/snap-cure epoxy composite was studied by subjecting 30° and 45° off-axis specimens to compression loading at high strain rates. Tests were performed using a compression split-Hopkinson pressure bar apparatus where an approximate axial strain rate of 305 s-1 was achieved. Images of the deformed specimen surfaces were captured with high-speed cameras and digital image correlation used to obtain a strain map. Pulse shaping was performed using a copper pulse shaper to achieve dynamic equilibrium during the high-rate tests. The results demonstrated that the in-plane shear yield stress and strength increased by 53% and 68%, respectively, when the strain rate increased from quasi-static to 305 s-1.

scholarly journals Strain field evolution at the ductile-to-brittle transition: a case study on ice

Solid Earth ◽  
2017 ◽  
Vol 8 (5) ◽  
pp. 943-953 ◽  
Author(s):  
Thomas Chauve ◽  
Maurine Montagnat ◽  
Cedric Lachaud ◽  
David Georges ◽  
Pierre Vacher
Keyword(s):  
Stress Concentration ◽  
Dynamic Recrystallization ◽  
Strain Field ◽  
Crack Opening ◽  
Local Stress ◽  
Image Correlation ◽  
Brittle Transition ◽  
Field Evolution ◽  
Crack Tips ◽  
Ductile To Brittle Transition

Abstract. This paper presents, for the first time, the evolution of the local heterogeneous strain field around intra-granular cracking in polycrystalline ice, at the onset of tertiary creep. Owing to the high homologous temperature conditions and relatively low compressive stress applied, stress concentration at the crack tips is relaxed by plastic mechanisms associated with dynamic recrystallization. Strain field evolution followed by digital image correlation (DIC) directly shows the redistribution of strain during crack opening, but also the redistribution driven by crack tip plasticity mechanisms and recrystallization. Associated local changes in microstructure induce modifications of the local stress field evidenced by crack closure during deformation. At the ductile-to-brittle transition in ice, micro-cracking and dynamic recrystallization mechanisms can co-exist and interact, the later being efficient to relax stress concentration at the crack tips.

Experimental Study on Bedding Plane Interfacial Slip

2012 ◽  
Vol 256-259 ◽  
pp. 298-301
Author(s):  
Shu Hong Dai ◽  
Ying Sun ◽  
Zi Xian Dong
Keyword(s):  
Rock Fracture ◽  
Correlation Method ◽  
Bedding Plane ◽  
Image Correlation ◽  
Interfacial Slip ◽  
Practical Applications ◽  
Three Point Bending ◽  
Natural Interface ◽  
Extension Direction ◽  
Rock Specimens

Interfacial slip in rock was studied utilizing digital image correlation method (DICM). Notched rock specimens consisting of a natural interface under three point bending were employed for researching the characters and mechanisms of the interfacial slip. The displacement and strain fields on the surface of specimen were measured accurately by DICM. The experimental results show that the interfacial slip can change the crack extension direction and mode. The results are helpful in researching the mechanism of interfacial slip and practical applications in rock fracture problems.

BEHAVIOR OF PLASTIC DEFORMATION AND CRACK PROPAGATION ON FULLY LAMELLAR GAMMA-TiAl ALLOY

2010 ◽  
Vol 24 (15n16) ◽  
pp. 2958-2963
Author(s):  
MING SONG ◽  
GUANGJIE MAO ◽  
YUE MA ◽  
SHENGKAI GONG
Keyword(s):  
Plastic Deformation ◽  
Plastic Zone ◽  
Strain Field ◽  
Tial Alloy ◽  
Image Correlation ◽  
Deformation Region ◽  
Order Of Magnitude ◽  
Plastic Deformation Region ◽  
Fully Lamellar

Practical residual strain field around the microcrack tip of fully lamellar γ- TiAl alloy was estimate the by digital image correlation (DIC) technology with in-situ SEM observation. And the macro plastic deformation before fracture of such low ductility alloys was observed. The results showed that the size of plastic zone around microcrack tip was 2 ~ 10µ m which was much more smaller than the calculated value by fracture mechanics. During the magnified observation on the plastic deformation region, a series of microcracks were observed in the specimen without macro cracking. Furthermore, the size of distribution region of the microcracks were in the same order of magnitude with the calculated plastic zone near primary crack tip which just reflected the comprehensive effect of microcracks and the plastic deformation on the tips of them.

Visualization of Particle-Toughening Mechanism in Transparent Polyurethanes

2014 ◽  
Author(s):  
Mohammad H. Malakooti ◽  
Patrick L. Anderson ◽  
Henry A. Sodano
Keyword(s):  
Brittle Fracture ◽  
Maximum Load ◽  
Compact Tension ◽  
Image Correlation ◽  
Toughening Mechanism ◽  
Two Phase ◽  
Practical Applications ◽  
Reduced Modulus ◽  
Drastic Increase ◽  
Ductile Behavior

Highly cross-linked polyurethanes have a high elastic modulus and creep resistance, but they undergo a brittle fracture below the glass transition temperature. Unfortunately, a large number of glassy polyurethanes are prone to brittle fracture without undergoing large elastic deformations; in particular, brittle failure is common under conditions such as low temperature and high strain rates. While the rigidity in polymers is required for practical applications, the lack of resistance against crack propagation is essential to avoid catastrophic failures. The toughening of polymers is a crucial aspect of improving the strength and ductility at specific temperatures and deformation rates. One method that has shown promise in recent years is the creation of local regions of reduced modulus that absorb strain energy and toughen the polymer. For instance, rubbers are typically added to epoxy which phase separate upon polymerization and create local elastic regions that significantly toughen the polymer. In this study, a variety of two-phase transparent polyurethanes in the form of single inclusions is designed to study the toughening mechanism of the local regions of reduced modulus with an embedded crack. Synthesized heterogeneous polyurethanes show a transition from brittle to ductile behavior in addition to a drastic increase in the maximum load that the polymer can withstand. Compact tension experiments demonstrate that a small reduction in the inclusion’s Young’s modulus (∼10%) leads to an increase in the toughness by factor of 7 (∼700%). Moreover, digital image correlation is performed to map the strain distribution around the crack in order to visualize possible toughening mechanism. Comparison between the induced strain field in samples with inclusion and samples without inclusion reveals an efficient toughening mechanism of the polymers.

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