scholarly journals Dynamice fracture in a semicristalline polymer: an analysis of the fracture surface

2021 ◽  
Vol 250 ◽  
pp. 06012
Author(s):  
Jean-Benoît Kopp ◽  
Jérémie Girardot
Keyword(s):  
Fracture Behaviour ◽  
Propagation Path ◽  
Local Velocity ◽  
Initiation Zone ◽  
Dynamic Fracture Tests ◽  
Initiation And Propagation ◽  
Fracture Tests ◽  
Propagation Zone ◽  
Specific Material ◽  
Local Speed

The fracture behaviour of a specific material, a semi-crystalline biobased polymer, was here studied. Dynamic fracture tests on strip band specimens were carried out. Fracture surfaces were observed at different scales by optical and electron microscopy to describe cracking scenarios. Crack initiation, propagation and arrest zones were described. Three distinct zones are highlighted in the initiation and propagation zone: a zone with conical markings, a mist zone and a hackle zone. The conical mark zone shows a variation in the size and density of the conical marks along the propagation path. This is synonymous with local speed variation. Microcracks at the origin of the conical marks in the initiation zone seem to develop from the nucleus of the spherulites. In the propagation zone with complex roughness, the direction of the microcracks and their cracking planes are highly variable. Their propagation directions are disturbed by the heterogeneities of the material. They branch or bifurcate at the level of the spherulites. In the arrest zone, the microcracks developed upstream continue to propagate in different directions. The surface created is increasingly smoother as the energy release rate decreases. It is shown that the local velocity of the crack varies in contrast to the macroscopic speed.

Quasi-Brittle Fracture of Lamellar γTiAl: Simulation Using a Cohesive Model with Stochastic Approach

2006 ◽  
Vol 324-325 ◽  
pp. 1317-1320
Author(s):  
R. Kabir ◽  
Alfred Cornec ◽  
Wolfgang Brocks
Keyword(s):  
Brittle Fracture ◽  
Element Model ◽  
Stochastic Approach ◽  
Cohesive Elements ◽  
Two Phase ◽  
Deformation And Fracture ◽  
Initiation And Propagation ◽  
Fracture Tests ◽  
Specific Material ◽  
Physical Phenomena

Quasi-brittle fracture of fully lamellar two phase (α2+γ)TiAl is investigated both experimentally and numerically. Fracture tests are conducted at room temperature, which fail in a quasi-brittle and unstable manner but exhibit significant variations in crack initiation and propagation prior to unstable failure. Fractographic investigations are performed which elucidate the micromechanical causes of the macroscopic behaviour. The observed deformation and fracture behaviours of the specimens are simulated by a finite element model containing cohesive elements for modelling the material separation. In order to capture the scatter of the macroscopic behaviour, a stochastic approach is chosen, in which local variations of cohesive parameters are taken into account. The model can describe and explain the physical phenomena of the specific material.

scholarly journals Effect of the Strain Rate on the Fracture Behaviour of High Pressure Pre-Charged Samples

Proceedings ◽  
2018 ◽  
Vol 2 (23) ◽  
pp. 1417
Author(s):  
Guillermo Álvarez Díaz ◽  
Tomás Eduardo García Suárez ◽  
Cristina. Rodríguez González ◽  
Francisco Javier Belzunce Varela
Keyword(s):  
Fracture Toughness ◽  
High Pressure ◽  
Hydrogen Embrittlement ◽  
Strain Rate ◽  
Fracture Behaviour ◽  
Structural Steels ◽  
Gaseous Hydrogen ◽  
Displacement Rate ◽  
Steel Strength ◽  
Fracture Tests

The aim of this work is to study the effect of the displacement rate on the hydrogen embrittlement of two different structural steels grades used in energetic applications. With this purpose, samples were pre-charged with gaseous hydrogen at 19.5 MPa and 450 °C for 21 h. Then, fracture tests of the pre-charged specimens were performed, using different displacement rates. It is showed that the lower is the displacement rate and the largest is the steel strength, the strongest is the reduction of the fracture toughness due to the presence of internal hydrogen.

Numerical Investigation of Adhesively Bonded Joints

2013 ◽  
Vol 392 ◽  
pp. 105-109
Author(s):  
Mahmood Mokhtari Hasan Abad ◽  
Reza Bakhtiari ◽  
Naghdali Choupani
Keyword(s):  
Mixed Mode ◽  
Fracture Behaviour ◽  
Mixed Mode Fracture ◽  
Bonded Joints ◽  
Adhesively Bonded ◽  
Adhesively Bonded Joints ◽  
Mode Fracture ◽  
Aerospace Material ◽  
Numerical Studies ◽  
Fracture Tests

The study focuses on using fracture mechanics to evaluate mixed-mode fracture properties of adhesively bonded aerospace material systems. As a part of experimental efforts, mixed-mode fracture tests were performed using modified Arcan specimens consisting of several combinations of adhesive, composite and metallic adherends using a special loading device. Experimental and numerical studies of mixed-mode fracture behaviour of adhesively bonded aluminum and steel were also performed using an adhesive in the aerospace industry. Finite element analyses were carried out on specimens with different adherends. Based on those analyses, many fundamental numerical results were obtained.

scholarly journals Hydrogen enhanced cracking studies on Fe–3wt%Si single and bi-crystal microcantilevers

2017 ◽  
Vol 375 (2098) ◽  
pp. 20160410 ◽  
Author(s):  
T. Hajilou ◽  
Y. Deng ◽  
N. Kheradmand ◽  
A. Barnoush
Keyword(s):  
Stress Concentration ◽  
Crack Initiation ◽  
The Other ◽  
Bending Test ◽  
Propagation Path ◽  
Transgranular Fracture ◽  
Post Mortem ◽  
Crack Initiation And Propagation ◽  
Initiation And Propagation

Hydrogen (H) enhanced cracking was studied in Fe–3wt%Si by means of in situ electrochemical microcantilever bending test. It was clearly shown that the presence of H causes hydrogen embrittlement (HE) by triggering crack initiation and propagation at the notch where stress concentration is existing. Additionally, the effect of carbon content and the presence of a grain boundary (GB) in the cantilever were studied. It was shown that in the presence of H the effect of carbon atom on pinning the dislocations is reduced. On the other hand, the presence of a GB, while the chemical composition of material kept constant, will promote the HE. Crack initiation and propagation occur in the presence of H, while the notch blunting was observed for both single and bi-crystalline beams bent in air. Post-mortem analysis of the crack propagation path showed that a transition from transgranular fracture to intragranular fracture mechanism is highly dependent on the position of the stress concentration relative to the GB. This article is part of the themed issue ‘The challenges of hydrogen and metals’.

scholarly journals Experimental and numerical study of the interaction between dynamically loaded cracks and pre-existing flaws in edge loaded PMMA specimens

2020 ◽  
Author(s):  
Chuzhali Nilath Irfan Habeeb ◽  
shmuel osovski
Keyword(s):  
Experimental Data ◽  
High Speed ◽  
Numerical Study ◽  
Damage Model ◽  
Image Correlation ◽  
High Speed Photography ◽  
Dynamic Fracture Tests ◽  
Micromechanical Damage ◽  
Fracture Tests ◽  
Micromechanical Damage Model

Dynamic fracture tests are carried out for four groups of hole-containing edge loaded specimens. The crack growth velocity, crack path, and dynamic toughness are extracted from the experiments using high-speed photography and digital image correlation. The importance of the interaction between the in-coming stress wave and the pre-existing hole is revealed and analyzed. A micromechanical damage model is calibrated to the experimental data from two of the specimens' designs and evaluated for its predictive capabilities using the other experimental configurations. The studied model is shown to be in reasonable agreement with the experimental data, and its limits are discussed

scholarly journals Numerical modelling strategies using implicit and explicit methods to simulate quasi-static and dynamic three-points bend fracture tests of a ductile steel

2021 ◽  
Vol 250 ◽  
pp. 02033
Author(s):  
Frédéric Nozères ◽  
Hervé Couque ◽  
Rémi Boulanger ◽  
Yann Quirion ◽  
Patrice Bailly ◽  
...  
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Crack Initiation ◽  
Crack Initiation And Propagation ◽  
Initiation And Propagation ◽  
Fracture Tests ◽  
Point Bend ◽  
Dynamic Loading Conditions ◽  
Implicit And Explicit ◽  
Static And Dynamic Loading

Three-point bend fracture tests have been conducted at different loading rates with a quadratic martensitic steel. The failure energy has been found to increase with loading rate. To get insights in this increase a numerical investigation has been undertaken with different strategies using ABAQUS and IMPETUS softwares in order to address quasi-static and dynamic loading conditions. Simulations were conducted with the ABAQUS software in order to carry out a comparative analysis of both implicit and explicit approaches. In addition to standard Finite Element Method (FEM) applied to quasi-static and dynamic conditions, the eXtended-Finite Element Method (X-FEM) was applied to quasistatic conditions. In both approaches, implicit and explicit, crack initiation and propagation were governed by a critical plastic strain threshold combined with a displacement-based damage evolution criterion. Simulations conducted with the IMPETUS software use an explicit approach and second order elements for both quasi-static and dynamic loading conditions. A node-splitting method using an energy-based damage criterion was employed to simulate the crack initiation and propagation. Experimental data and numerical results have been compared, allowing to determine the ability of these two softwares to simulate accurately three-point bend fracture tests.

The Creep and Fracture Behaviour of the Polyethylene PE100

2013 ◽  
Vol 577-578 ◽  
pp. 653-656
Author(s):  
Ivica Skozrit ◽  
Zdenko Tonković ◽  
Janos Kodvanj
Keyword(s):  
Fracture Behaviour ◽  
Numerical Study ◽  
Tensile Specimen ◽  
Experimental Results ◽  
Constitutive Law ◽  
Secondary Creep ◽  
User Subroutine ◽  
Fracture Tests ◽  
Creep Constitutive Model ◽  
Cracked Specimens

This paper presents an experimental and numerical study on the creep and fracture behaviour of the polyethylene PE100. The experimental procedure includes monotonic tests on the standard tensile specimen as well as creep-fracture tests on the axisymmetrically cracked specimens. Based on the experimental results, a new primary/secondary creep constitutive model is proposed to simulate the nonlinear and time dependent behaviour of considered material. The material parameters are computed from a leastsquare fit to experimental data obtained from tests at 80 °C. Within the framework of numerical investigations an algorithm for the integration of the constitutive law is derived. The derived algorithm in conjunction with the consistent tangent matrix is implemented in the finite element (FE) code ABAQUS by using the user subroutine CREEP. The accuracy of the proposed numerical algorithm is validated by comparing with experimental results.

Action Potential Initiation and Propagation in CA3 Pyramidal Axons

2007 ◽  
Vol 97 (5) ◽  
pp. 3460-3472 ◽  
Author(s):  
Julian P. Meeks ◽  
Steven Mennerick
Keyword(s):  
Sodium Channel ◽  
Conduction Velocity ◽  
Initiation Site ◽  
Initiation Zone ◽  
Initiation And Propagation ◽  
Threshold Crossing ◽  
Action Potential Initiation ◽  
Ca3 Neurons ◽  
Zone Characteristic ◽  
Spike Initiation

Thin, unmyelinated axons densely populate the mammalian hippocampus and cortex. However, the location and dynamics of spike initiation in thin axons remain unclear. We investigated basic properties of spike initiation and propagation in CA3 neurons of juvenile rat hippocampus. Sodium channel alpha subunit distribution and local applications of tetrodotoxin demonstrate that the site of first threshold crossing in CA3 neurons is ∼35 μm distal to the soma, somewhat more proximal than our previous estimates. This discrepancy can be explained by the finding, obtained with simultaneous whole cell somatic and extracellular axonal recordings, that a zone of axon stretching to ∼100 μm distal to the soma reaches a maximum rate of depolarization nearly synchronously by the influx of sodium from the high-density channels. Models of the proximal axon incorporating observed distributions of sodium channel staining recapitulated salient features of somatic and axonal spike waveforms, including the predicted initiation zone, characteristic spike latencies, and conduction velocity. The preferred initiation zone was unaltered by stimulus strength or repetitive spiking, but repetitive spiking increased threshold and significantly slowed initial segment recruitment time and conduction velocity. Our work defines the dynamics of initiation and propagation in hippocampal principal cell axons and may help reconcile recent controversies over initiation site in other axons.

The Measurement of High Speed Air Velocity and Temperature using Sound Wave Photography

1955 ◽  
Vol 6 (3) ◽  
pp. 181-195 ◽  
Author(s):  
D. E. Elliott
Keyword(s):  
Sound Wave ◽  
High Speed ◽  
Time Interval ◽  
Short Time Interval ◽  
Local Velocity ◽  
Air Velocity ◽  
Air Stream ◽  
Short Time ◽  
Further Development ◽  
Local Speed

SummaryA transient sound wave is generated by discharging a spark in an air stream, the velocity and temperature of which are required. After a time interval of about 25 microseconds a shadowgraph photograph of the sound wave is taken; a second photograph is obtained after a further known time interval of the same order. The two exposures, both on the same negative, show the propagation of the sound wave in the air stream and from this the Mach number, the true velocity, the local velocity of sound, and hence the temperature, can be calculated.Using this method, measurements of Mach numbers of the order of 0·5 gave values between 98 per cent, and 100 per cent, of those calculated from pressure measurements. Typical examples of the sound wave photographs are shown. With further development along the lines indicated in the paper greater accuracy should be possible. The local speed of sound was measured to an estimated accuracy of ±1·5 per cent.Since only a very short time interval is needed to obtain the photographs, the method appears promising for investigating explosions of brief duration, or dealing with flows of pulsating character.

Sign in / Sign up

Export Citation Format

Share Document