scholarly journals Non steady-state intersonic cracks in elastomer membranes under large static strain

2021 ◽  
Author(s):  
Thomas Corre ◽  
Michel Coret ◽  
Erwan Verron ◽  
Bruno Leblé
Keyword(s):  
Steady State ◽  
Crack Propagation ◽  
Crack Path ◽  
Stretch Ratio ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Crack Speed ◽  
Propagation Regime ◽  
Acceleration And Deceleration ◽  
International Audience

International audience Dynamic crack propagation in elastomer membranes is investigated; the focus is laid on cracks reaching the speed of shear waves in the material. The specific experimental setup developed to measure crack speed is presented in details. The protocol consists in (1) stretching an elastomer membrane under planar tension loading conditions, then (2) initiating a small crack on one side of the membrane. The crack speed is measured all along the crack path in both reference and actual configurations, including both acceleration and deceleration phases, i.e. non steady-state crack propagation phases. The influence of the prescribed stretch ratio on crack speed is analysed in the light of both these new experiments and the few previously published studies. Conclusions previously drawn for steady-state crack growth are extended to non steady-state conditions: stretch perpendicular to the crack path governs crack speed in intersonic crack propagation regime, and the role of the stretch in crack direction is minor.

Fractography of Dynamic Crack Propagation in Silicon Crystal

2009 ◽  
Vol 409 ◽  
pp. 55-64 ◽  
Author(s):  
Dov Sherman
Keyword(s):  
Crack Propagation ◽  
Amorphous Materials ◽  
Crack Path ◽  
Silicon Crystal ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Low Velocity ◽  
Velocity Surface ◽  
Path Instabilities ◽  
New Phenomena

The phenomena occurring during rapid crack propagation in brittle single crystals were studied by cleaving silicon specimens on the low energy cleavage planes under tensile and bending. The experiments revealed new phenomena not previously reported, and new crack path instabilities in particular. The well defined boundary conditions of the tested specimens and crack velocity measurements enabled rationalization of the observed phenomena and the velocity-surface instabilities relationship in particular. In contrast to amorphous materials, the observed instabilities are generated at relatively low velocity, while at high velocity the crack path remains stable. No evidences for mirror, mist, and hackle instabilities, typical in amorphous materials, were found.

Modeling Intersonic Crack Propagation in Fiber Reinforced Composites With Contact/Cohesive Laws

2001 ◽  
Author(s):  
S. K. Dwivedi ◽  
H. D. Espinosa
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Epoxy Composite ◽  
Dynamic Crack Propagation ◽  
Interface Element ◽  
Dynamic Crack ◽  
Crack Speed ◽  
Interface Elements ◽  
Intersonic Crack Propagation ◽  
The Impact

Abstract Dynamic crack propagation in an unidirectional Carbon/Epoxy composite is studied through finite element analyses in total Lagrangian co-ordinates. A finite deformation anisotropic visco-plastic model is used to describe the constitutive response of the composite. Crack initiation and propagation is simulated by embedding zero thickness interface element along the possible crack path. An irreversible cohesive law is used to describe the evolution of normal and shear tractions as a function of displacement jumps. The compressive response prior to interface failure is analyzed using contact impenetrability conditions. The failure of the first interface element at the pre-notch tip models crack initiation. Crack propagation is modeled through consecutive failure of interface elements. Dynamic crack propagation phenomena are studied in terms of crack initiation time, crack speed, mode I and mode II displacement jumps and tractions associated with the failure of interface elements, effective plastic strain at the crack tip and path independent integral J′. Analyses are first carried out for the dynamic crack propagation along bi-material interfaces. The results obtained from present analyses agree well with literature data. Detailed analyses are carried out for a pre-notched unidirectional Carbon/Epoxy composite material. The impact velocity in the analyses is an imposed velocity over an assumed impact region and remains constant throughout the analysis. Analyses are carried out at impact velocities of 5, 10, 20, 30 and 40 m/s, assuming the crack wake is frictionless. Moreover, analyses at impact velocities of 30 and 40 m/s are also carried out with a friction coefficient of 0.5 along the crack surfaces. The analyses established intersonic crack speed in the fiber reinforced composite material. Intersonic crack propagation for the impact velocities of 40 m/s is 400% of the shear wave speed and 87% of the longitudinal wave speed. Detailed discussion is given on the features of sub-sonic and intersonic crack propagation in Carbon/Epoxy composite materials. It is shown that the friction coefficient along the crack surface plays an important role by smearing the discontinuous field that develops behind the crack tip and by reducing crack speed in the intersonic regime. The analyses show that the contour integral J′ computed at near field contours are path independent and can serve as a parameter for characterizing intersonic crack propagation.

Specimen Geometry Effects on Dynamic Crack Propagation

2006 ◽  
Vol 326-328 ◽  
pp. 911-914
Author(s):  
Kazuo Arakawa ◽  
Toshio Mada
Keyword(s):  
Crack Propagation ◽  
High Speed ◽  
Dynamic Stress Intensity Factor ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Acceleration Process ◽  
Fracture Event ◽  
Acceleration And Deceleration ◽  
Event Dynamic ◽  
Crack Acceleration

Dynamic crack propagation in PMMA was studied using the method of caustics in combination with a Cranz-Schardin type high-speed camera. Three different types of specimen geometries were employed to achieve the crack acceleration, deceleration and re-acceleration process in one fracture event. Dynamic stress intensity factor KID and the crack velocity were evaluated in the course of crack propagation to obtain the relationship between KID and the velocity The effect of crack acceleration and deceleration on the KID -velocity relations was examined.

scholarly journals Dynamic crack propagation in weak snowpack layers: insights from high-resolution, high-speed photography

2021 ◽  
Vol 15 (7) ◽  
pp. 3539-3553
Author(s):  
Bastian Bergfeld ◽  
Alec van Herwijnen ◽  
Benjamin Reuter ◽  
Grégoire Bobillier ◽  
Jürg Dual ◽  
...  
Keyword(s):  
High Resolution ◽  
Crack Propagation ◽  
Fracture Energy ◽  
High Speed ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Crack Speed ◽  
Weak Layer ◽  
Specific Fracture ◽  
Insight Into

Abstract. Dynamic crack propagation in snow is of key importance for avalanche release. Nevertheless, it has received very little experimental attention. With the introduction of the propagation saw test (PST) in the mid-2000s, a number of studies have used particle tracking analysis of high-speed video recordings of PST experiments to study crack propagation processes in snow. However, due to methodological limitations, these studies have provided limited insight into dynamical processes such as the evolution of crack speed within a PST or the touchdown distance, i.e. the length from the crack tip to the trailing point where the slab comes to rest on the crushed weak layer. To study such dynamical effects, we recorded PST experiments using a portable high-speed camera with a horizontal resolution of 1280 pixels at rates of up to 20 000 frames s−1. We then used digital image correlation (DIC) to derive high-resolution displacement and strain fields in the slab, weak layer and substrate. The high frame rates enabled us to calculate time derivatives to obtain velocity and acceleration fields. We demonstrate the versatility and accuracy of the DIC method by showing measurements from three PST experiments, resulting in slab fracture, crack arrest and full propagation. We also present a methodology to determine relevant characteristics of crack propagation, namely the crack speed (20–30 m s−1), its temporal evolution along the column and touchdown distance (2.7 m) within a PST, and the specific fracture energy of the weak layer (0.3–1.7 J m−2). To estimate the effective elastic modulus of the slab and weak layer as well as the weak layer specific fracture energy, we used a recently proposed mechanical model. A comparison to already-established methods showed good agreement. Furthermore, our methodology provides insight into the three different propagation results found with the PST and reveals intricate dynamics that are otherwise not accessible.

scholarly journals Micro-mechanical Insights Into the Dynamics of Crack Propagation in Snow Fracture Experiments

2021 ◽  
Author(s):  
Grégoire Bobillier ◽  
Bastian Bergfeld ◽  
Jürg Dual ◽  
Johan Gaume ◽  
Alec Herwijnen ◽  
...  
Keyword(s):  
Steady State ◽  
Crack Propagation ◽  
Field Experiments ◽  
Process Zone ◽  
Crack Tip ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Stress Concentrations ◽  
Weak Layer ◽  
Mountainous Regions

Abstract Dry-snow slab avalanches result from the propagation of compacting shear bands in highly porous weak layers buried within a stratified and metastable snowpack. While our understanding of slab avalanche mechanisms improved with recent experimental and numerical advances, fundamental micro-mechanical processes remain poorly understood due to a lack of non-invasive monitoring techniques. Using a novel discrete micro-mechanical model, we reproduced crack propagation dynamics observed in field experiments, which employ the propagation saw test. The detailed microscopic analysis of weak layer stresses and bond breaking allowed us to define the crack tip location of closing crack faces, analyze its spatio-temporal characteristics and monitor the evolution of stress concentrations and the fracture process zone both in transient and steady-state regimes. Results highlight the occurrence of a steady state in crack speed and stress conditions for sufficiently long distances of crack propagation (> 4 m). Crack propagation without external driving shear force is possible due to the local mixed-mode shear-compression stress nature at the crack tip induced by slab bending and weak layer volumetric collapse. Our result shed light into the microscopic origin of dynamic crack propagation in snow slab avalanche release that eventually will improve the evaluation of avalanche release sizes and thus hazard management and forecasting in mountainous regions.

scholarly journals Micro-mechanical insights into the dynamics of crack propagation in snow fracture experiments

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Grégoire Bobillier ◽  
Bastian Bergfeld ◽  
Jürg Dual ◽  
Johan Gaume ◽  
Alec van Herwijnen ◽  
...  
Keyword(s):  
Steady State ◽  
Crack Propagation ◽  
Field Experiments ◽  
Process Zone ◽  
Crack Tip ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Stress Concentrations ◽  
Weak Layer ◽  
Mountainous Regions

AbstractDry-snow slab avalanches result from crack propagation in a highly porous weak layer buried within a stratified and metastable snowpack. While our understanding of slab avalanche mechanisms improved with recent experimental and numerical advances, fundamental micro-mechanical processes remain poorly understood due to a lack of non-invasive monitoring techniques. Using a novel discrete micro-mechanical model, we reproduced crack propagation dynamics observed in field experiments, which employ the propagation saw test. The detailed microscopic analysis of weak layer stresses and bond breaking allowed us to define the crack tip location of closing crack faces, analyze its spatio-temporal characteristics and monitor the evolution of stress concentrations and the fracture process zone both in transient and steady-state regimes. Results highlight the occurrence of a steady state in crack speed and stress conditions for sufficiently long crack propagation distances (> 4 m). Crack propagation without external driving force except gravity is possible due to the local mixed-mode shear-compression stress nature at the crack tip induced by slab bending and weak layer volumetric collapse. Our result shed light into the microscopic origin of dynamic crack propagation in snow slab avalanche release that eventually will improve the evaluation of avalanche release sizes and thus hazard management and forecasting in mountainous regions.

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