Changes in the mechanical properties of snow relevant to crack propagation in the hours and minutes following loading

2020 ◽  
Author(s):  
Karl W. Birkland ◽  
Bastian Bergfeld ◽  
Alec van Herwijnen
Keyword(s):  
Mechanical Properties ◽  
Crack Propagation ◽  
High Speed ◽  
Propagation Speed ◽  
Temporal Changes ◽  
Image Correlation ◽  
Additional Information ◽  
The Hours ◽  
Crack Propagation Speed ◽  
Specific Fracture

<p>Since most dry slab avalanches occur during or immediately following loading by snowfall or wind deposition, it is important to understand changes in the mechanical properties of the snowpack in the minutes and hours following loading. To investigate these temporal changes we conducted a series of 15 Propagation Saw Test (PST) experiments on a flat, uniform site. The existing snowpack at our site contained a layer of surface hoar buried 2 cm below the snow surface. We used a 5 mm sieve to add 10 cm of snow into a 120 cm by 30 cm cardboard frame and completely isolated our blocks. We then conducted PSTs on the buried surface hoar layer from 4 – 453 minutes after adding the sieved snow. We sprayed dye on the side of our tests and filmed them with a high speed camera at 3000 frames per second. Immediately following our tests we measured the density of the sieved snow, and we collected three SnowMicroPen (SMP) profiles along the length of each PST. In one case we collected SMP data at 10 cm increments along our beam prior to conducing our PST to better assess vertical and lateral variations in slab properties induced by sieving. We utilize Digital Image Correlation analyses of the high speed videos to assess the slab elastic modulus (E), the weak layer specific fracture energy (wf), and the crack propagation speed (c) of each test. All our tests fully propagated to the end of the PST columns. Critical cut lengths (rc) ranged between 1.5 and 9 cm, with rc generally increasing over time, in line with the gradual stiffening of the slab observed in the SMP measurements. Our results provide additional information about the temporal changes of mechanical properties immediately following loading, and will better inform modeling efforts attempting to assess these changes.</p>

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

2021 ◽  
Author(s):  
Bastian Bergfeld ◽  
Alec van Herwijnen ◽  
Benjamin Reuter ◽  
Grégoire Bobillier ◽  
Jürg Dual ◽  
...  
Keyword(s):  
High Resolution ◽  
Crack Propagation ◽  
Fracture Energy ◽  
High Speed ◽  
Image Correlation ◽  
Crack Speed ◽  
Specific Fracture Energy ◽  
Weak Layer ◽  
Specific Fracture ◽  
Insight Into

Abstract. To assess snow avalanche release probability, information on failure initiation and crack propagation in weak snowpack layers underlying cohesive slab layers are required. With the introduction of the Propagation Saw Test (PST) in the mid-2000s, various studies used particle tracking analysis of high-speed video recordings of PST experiments to gain insight into crack propagation processes, including slab bending, weak layer collapse, crack propagation speed and the frictional behavior after weak layer fracture. However, the resolution of the videos and the methodology used did not allow insight into dynamic processes such as the evolution of crack speed within a PST or the touchdown distance, which is the length from the crack tip to the trailing point where the slab sits on the crushed weak layer at rest again. Therefore, to study the dynamics of crack propagation we recorded PST experiments using a powerful portable high-speed camera with a horizontal resolution of 1280 pixels at rates up to 20,000 frames per second. By applying a high-density speckling pattern on the entire PST column, 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 allowed time derivatives to obtain velocity and acceleration fields. On the one hand, we demonstrate the versatile capabilities and accuracy of the DIC method by showing three PST experiments resulting in slab fracture, crack arrest and full propagation. On the other hand, we present a methodology to determine relevant characteristics of crack propagation: the crack speed and touchdown distance within a PST, and the specific fracture energy of the weak layer. 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 also provides insight into the three different propagation results found with the PST and reveals intricate dynamics that are otherwise not accessible.

Investigation of Crack Propagation Characteristics Using Instrumented Charpy and DWT Tests for Full-Scale Burst Tested 1219 mm OD Grade 550 (X80) Linepipe

2016 ◽  
Author(s):  
Satoshi Igi ◽  
Cindy Guan ◽  
Brian Rothwell ◽  
Takashi Hiraide
Keyword(s):  
Crack Propagation ◽  
High Speed ◽  
Large Diameter ◽  
Propagation Speed ◽  
Test Site ◽  
Management Program ◽  
Full Scale ◽  
In Situ Observation ◽  
Separation Index ◽  
Crack Propagation Speed

TransCanada, on behalf of the Coastal GasLink (CGL) project, has carried out two full-scale burst tests [1, 2] at the Spadeadam test site of DNV GL, to validate the effectiveness of crack arrestors and refine the propagation control design for the large-diameter, X80 linepipe required for this project. The tests were supported by LNG Canada and TransCanada Technology Management Program. For these full-scale burst tests, Grade 550linepipe having Charpy energies from 125 to over 450 J were produced using thermomechanical controlled processing (TMCP) technology. This paper describes propagation and arrest properties of the X80 linepipe materials having various Charpy energy values from the aspect of crack propagation energy and crack propagation speed relationships from instrumented Charpy and press-notched (PN) and static pre-cracked drop-weight tear (SPC-DWT) tests, together with in-situ observation of crack propagation by high-speed video camera. It was found that crack propagation speed is greatly affected by crack propagation energy measured by both Charpy and instrumented DWT tests. The crack propagation energy is lower in DWTT specimens with a higher separation index. It is not clear whether the crack propagation energy is only affected by the separations. However, the crack velocity is higher in DWTT specimens with a higher separation index. It is assumed that the crack propagation speed might be not only affected by separation but also low propagation energy. The testing data obtained from Charpy and instrumented DWT tests are compared with the fracture speed data measured from the full-scale burst test. The correlation between Charpy energy and crack propagation energy in DWTT is also compared with the predictions of an empirical equation.

Local Elasto-Plastic Identification of the Behaviour of Friction Stir Welds with the Virtual Fields Method

2011 ◽  
Vol 70 ◽  
pp. 135-140 ◽  
Author(s):  
G. Le Louëdec ◽  
M.A. Sutton ◽  
Fabrice Pierron
Keyword(s):  
Mechanical Properties ◽  
Digital Image Correlation ◽  
Digital Image ◽  
High Speed ◽  
Weld Zone ◽  
Spatial Variations ◽  
Image Correlation ◽  
Virtual Fields Method ◽  
Full Field ◽  
Friction Stir

Welding is one of the most popular joining technologies in industry. Depending on the materials to be joined, the geometry of the parts and the number of parts to be joined, there is a wide variety of methods that can be used. These joining techniques share a common feature: the material in the weld zone experiences different thermo-mechanical history, resulting in significant variations in material microstructure and spatial heterogeneity in mechanical properties. To optimize the joining process, or to refine the design of welded structures, it is necessary to identify the local mechanical properties within the different regions of the weld. The development of full-field kinematic measurements (digital image correlation, speckle interferometry, etc.) helps to shed a new light on this problem. The large amount of experimental information attained with these methods makes it possible to visualize the spatial distribution of strain on the specimen surface. Full-field kinematic measurements provide more information regarding the spatial variations in material behaviour. As a consequence, it is now possible to quantify the spatial variations in mechanical properties within the weld region through a properly constructed inverse analysis procedure. High speed tensile tests have been performed on FSW aluminium welds. The test was performed on an MTS machine at a cross-head speed of up to 76 mm/s. Displacement fields were measured across the specimen by coupling digital image correlation with a high-speed camera (Phantom V7.1) taking 1000 frames per second. Then, through the use of the virtual fields method it is possible to retrieve the mechanical parameters of the different areas of the weld from the strain field and the loading. The elastic parameters (Young’s modulus and Poisson’s ratio) are supposed to be constant through the weld. Their identification was carried out using the virtual fields method in elasticity using the data of the early stage of the experiment. Assuming that the mechanical properties (elastic and plastic) of the weld are constant through the thickness, the plastic parameters were identified on small sections through the specimen, using a simple linear hardening model. This method leads to a discrete identification of the evolution of the mechanical properties through the weld. It allows the understanding of the slight variations of yield stress and hardening due to the complexity of the welding process.

scholarly journals Crack propagation speed in ceramic during quenching

2018 ◽  
Vol 38 (7) ◽  
pp. 2879-2885 ◽  
Author(s):  
Yingfeng Shao ◽  
Boyang Liu ◽  
Xiaohuan Wang ◽  
Long Li ◽  
Jiachen Wei ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Propagation Speed ◽  
Crack Propagation Speed

Effect of Contact between the Crack Faces on Crack Propagation

2013 ◽  
Vol 577-578 ◽  
pp. 61-64 ◽  
Author(s):  
Guido Dhondt
Keyword(s):  
Crack Propagation ◽  
Propagation Speed ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Contact Conditions ◽  
Contact Formulation ◽  
Positive Mode ◽  
Crack Propagation Speed ◽  
Crack Faces ◽  
Realistic Prediction

In mixed-mode crack propagation the crack faces frequently touch each other. The ensuing friction is expected to decrease the crack propagation speed. This effect is usually not taken into account, however, a realistic prediction of this effect may increase the calculated life and consequently increase the length of the inspection intervals. In this paper, penalty contact conditions are introduced in between the crack faces of the automatically generated mesh in a cyclic crack propagation. Special attention is given to the contact formulation and the area in which contact is defined. It is shown that the resulting crack propagation rate is significantly reduced by the introduction of friction provided that positive Mode-I is not significantly involved.

scholarly journals Temporal changes in the mechanical properties of snow related to crack propagation after loading

2019 ◽  
Vol 159 ◽  
pp. 142-152 ◽  
Author(s):  
Karl W. Birkeland ◽  
Alec van Herwijnen ◽  
Benjamin Reuter ◽  
Bastian Bergfeld
Keyword(s):  
Mechanical Properties ◽  
Crack Propagation ◽  
Temporal Changes

Detection of Reinforced Concrete Crack Using Mechano-Luminescence Paint

2013 ◽  
Vol 316-317 ◽  
pp. 1049-1054 ◽  
Author(s):  
Il Young Jang ◽  
Seong Kyum Kim ◽  
Ji Sik Kim ◽  
Ki Yong Ann ◽  
Chang Geun Cho
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Reinforced Concrete ◽  
Propagation Speed ◽  
Bending Test ◽  
Reinforced Concrete Structures ◽  
Concrete Material ◽  
Concrete Crack ◽  
Concrete Materials ◽  
Crack Propagation Speed

As a nonuniform and unisotropic material with a relatively low tensile strength in spite of high compression strength, a concrete material is vulnerable to bending and tension. Due to the mechanical properties of the current reinforced concrete structures, it is hard for concrete materials to avoid the damages caused by cracks. Although cracks are the easiest things to detect and the most effectively repairable things due to their characteristics, it is very hard to measure them efficiently. In this research, the author measured cracks by visualizing them through mechano- luminescence(ML) paint. By applying ML paint on the surface of the specimen and using the 3-point bending test, the author conducted a quantitative evaluation on the mechanical properties of cracks such as the cracking aspect and length of reinforced concrete. Through the results of this research, the author confirmed the crack propagation speed by section and the mechanical correlation such as between loads and cracks and between deflection and cracks, which means this research was quite successful in analyzing the characteristics of cracks.

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