scholarly journals Estimation of Fracture Toughness by Testing Notched Fracture Specimens and Applying the Theory of Critical Distances

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
S. Cicero ◽  
V. Madrazo ◽  
I. A. Carrascal
Keyword(s):  
Fracture Toughness ◽  
Finite Elements ◽  
Critical Distance ◽  
Stress Fields ◽  
Finite Elements Analysis ◽  
Notched Specimens ◽  
Apparent Fracture Toughness ◽  
Validity Range ◽  
Finite Elements Simulation ◽  
Fracture Specimens

This paper applies a methodology that allows the fracture toughness of a given material to be estimated by testing notched fracture toughness specimens and applying the Theory of Critical Distances, which requires the elastic stress field at the notch tip to be determined by finite elements simulation. This methodology, which is not intended to substitute any standardised fracture characterisation procedure, constitutes an alternative in those situations where pre-cracking processes may be too time-consuming, too expensive or, simply, cannot be performed. It comprises testing two notched specimens with different notch radii, defining the corresponding stress fields at fracture by using finite elements analysis, and applying the Theory of Critical Distances in order to calibrate the material’s critical distance and to apply the corresponding apparent fracture toughness formulation. The methodology has been applied to two different materials, PMMA and Al7075-T651, and the results have proven that, as long as the Theory of Critical Distances has been applied within its validity range, the fracture toughness estimations are highly accurate.

scholarly journals Probabilistic Assessment of Fracture Toughness of Epoxy Resin EPOLAM 2025 Including the Notch Radii Effect

Polymers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1857
Author(s):  
Adrián Álvarez-Vázquez ◽  
Miguel Muñiz-Calvente ◽  
Pelayo Fernández Fernández ◽  
Alfonso Fernández-Canteli ◽  
María Jesús Lamela-Rey ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Critical Distance ◽  
Polymer Materials ◽  
Cumulative Distribution ◽  
Probabilistic Assessment ◽  
Apparent Fracture Toughness ◽  
Experimental Campaign ◽  
Failure Assessment ◽  
Alternative Approaches ◽  
Reliable Design

Many design scenarios of components made of polymer materials are concerned with notches as representative constructive details. The failure hazard assessment of these components using models based on the assumption of cracked components leads to over-conservative failure estimations. Among the different alternative approaches proposed that are based on the apparent fracture toughness, KcN is considered. In so doing, the current deterministic underlying concept must be replaced by a probabilistic one to take into account the variability observed in the failure results in order to ensure a reliable design. In this paper, an approach based on the critical distance principle is proposed for the failure assessment of notched EPOLAM 2025 CT samples with each different notch radii (ρ) including a probabilistic assessment of the failure prediction. First, each apparent fracture toughness is transformed into the equivalent fracture toughness for ρ=0 based on the critical distances theory. Then, once all results are normalized to the same basic conditions, a Weibull cumulative distribution function is fitted, allowing the probability of failure to be predicted for different notch radii. In this way, the total number of the specimens tested in the experimental campaign is reduced, whereas the reliability of the material characterization improves. Finally, the applicability of the proposed methodology is illustrated by an example using the own experimental campaign performed on EPOLAM 2025 CT specimens with different notch radii (ρ).

scholarly journals Critical Distance Default Values for Structural Steels and a Simple Formulation to Estimate the Apparent Fracture Toughness in U-Notched Conditions

Metals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 871 ◽  
Author(s):  
Sergio Cicero ◽  
Juan Fuentes ◽  
Isabela Procopio ◽  
Virginia Madrazo ◽  
Pablo González
Keyword(s):  
Fracture Toughness ◽  
Structural Integrity ◽  
Critical Distance ◽  
Structural Steels ◽  
Simple Formulation ◽  
Integrity Assessment ◽  
Apparent Fracture Toughness ◽  
Linear Behavior ◽  
Macro Scale ◽  
Failure Loads

The structural integrity assessment of components containing notch-type defects has been the subject of extensive research in the last few decades. The assumption that notches behave as cracks is generally too conservative, making it necessary to develop assessment methodologies that consider the specific nature of notches, providing accurate safe predictions of failure loads or defect sizes. Among the different theories or models that have been developed to address this issue the Theory of Critical Distances (TCD) is one of the most widely applied and extended. This theory is actually a group of methodologies that have in common the use of the material toughness and a length parameter that depends on the material (the critical distance; L). This length parameter requires calibration in those situations where there is a certain non-linear behavior on the micro or the macro scale. This calibration process constitutes the main practical barrier for an extensive use of the TCD in structural steels. The main purpose of this paper is to provide, through a set of proposed default values, a simple methodology to accurately estimate both the critical distance of structural steels and the corresponding apparent fracture toughness predictions derived from the TCD.

Analysis of Notch Effect in Fracture Micromechanisms

2012 ◽  
Author(s):  
Sergio Cicero ◽  
Virginia Madrazo ◽  
Isidro Carrascal ◽  
Roman Cicero
Keyword(s):  
Fracture Toughness ◽  
Aluminum Alloy ◽  
Critical Radius ◽  
High Strength ◽  
Fracture Mechanisms ◽  
Notch Effect ◽  
Progressive Change ◽  
Load Bearing Capacity ◽  
Notched Specimens ◽  
Apparent Fracture Toughness

This paper presents an analysis of the notch effect in fracture micromechanisms. To this end, experimental results obtained in notched specimens are presented, together with the corresponding stress field at fracture and the SEM fractographies. The specimens comprise three materials (structural steel S275JR, high-strength aluminum alloy Al7075-T651 and Polymethyl methacrylate-PMMA) and notch radii varying from 0 mm (cracks) up to 2.5 mm. The results show how the stress relaxation caused by the notch effect is accompanied by a progressive change in the fracture mechanisms, from basically brittle ones in cracked conditions (for the three materials analyzed) to non-linear mechanisms observed for high notch radii, which explain the increase caused by the notch effect in both the load bearing capacity and the apparent fracture toughness. Also the concept of critical radius, that one below which the notch effect is negligible, is justified by SEM observations.

Structural Micro-Layered Ceramics with Surfaces under Tension and Compression with Increasing Apparent Fracture Toughness

2007 ◽  
Vol 336-338 ◽  
pp. 2564-2568 ◽  
Author(s):  
Jakob Kübler ◽  
Gurdial Blugan ◽  
Hans Jelitto ◽  
Gerold A. Schneider ◽  
Richard Dobedoe
Keyword(s):  
Fracture Toughness ◽  
Testing Machine ◽  
High Fracture Toughness ◽  
High Fracture ◽  
Notched Specimens ◽  
Apparent Fracture Toughness ◽  
Tension And Compression ◽  
Different Depths ◽  
Layered Ceramics ◽  
Stiff Testing Machine

Two different designs of high fracture toughness micro-laminate ceramics were produced containing 50 μm thick Si3N4 layers and 100 μm thick Si3N4 + TiN layers. The first design with external tensile layers had a predicted maximum apparent fracture toughness of 10.5 MPa m1/2. The second design with external compressive layers had a predicted maximum apparent fracture toughness of 18.0 MPa m1/2. The fracture toughness of these micro-laminates was tested by the SEVNB method. A stiff testing machine was used to measure the R-curve behavior by observing crack growth in single notched specimens. A soft testing machine was used to measure the R-curve behavior using several specimens with notches at different depths.

A SPLINES BASED METHOD FOR MODELING THE HUMAN HEAD FOR USE IN FINITE ELEMENTS ANALYSIS

2017 ◽  
Author(s):  
Daniel Ponce ◽  
Eduardo Szpoganicz ◽  
Leonardo Mejia Rincon ◽  
Ernesto Ponce Lopez
Keyword(s):  
Finite Elements ◽  
Human Head ◽  
Finite Elements Analysis
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