scholarly journals Estimation of the Onset of Crack Growth in Ductile Materials

2018 ◽  
Author(s):  
Andrzej Neimitz ◽  
Jaroslaw Galkiewicz ◽  
Sebastian Lipiec ◽  
Ihor Dzioba
Keyword(s):  
Plastic Strain ◽  
Ductile Fracture ◽  
Crack Front ◽  
Stress Triaxiality ◽  
Critical Value ◽  
Effective Plastic Strain ◽  
Ductile Materials ◽  
Different Temperatures ◽  
Fracture Tests ◽  
Lode Angle

In this paper, the ductile fracture mechanism is discussed. The results of the numerical and experimental analyses are used to estimate of the onset of the crack front growth . It is assumed that the ductile fracture in front of the crack starts at the location along the crack front where the accumulated effective plastic strain reaches a critical value. It is also assumed that the critical effective plastic strain depends on the stress triaxiality and the Lode angle. The experimental programme was performed using five different specimen geometries, three different materials and three different temperatures of +20°C, -20°C and -50°C. Using the experimental data and the results of the finite element computations, the critical effective plastic strains are determined for each material and each temperature. However, before the critical effective plastic strain is determined, a careful calibration of the stress–strain curves was performed after modification of the Bai–Wierzbicki procedure. Finally, by analysing the experimental results recorded during the interrupted fracture tests and scanning microscopy observations, the research hypothesis is verified.

scholarly journals Estimation of the Onset of Crack Growth in Ductile Materials

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2026 ◽  
Author(s):  
Andrzej Neimitz ◽  
Jaroslaw Galkiewicz ◽  
Sebastian Lipiec ◽  
Ihor Dzioba
Keyword(s):  
Plastic Strain ◽  
Ductile Fracture ◽  
Crack Growth ◽  
Crack Front ◽  
Stress Triaxiality ◽  
Experimental Program ◽  
Effective Plastic Strain ◽  
Ductile Materials ◽  
Ductile Crack Growth ◽  
Different Temperatures

In this paper, the ductile fracture mechanism is discussed. The results of numerical and experimental analyses were used to estimate the onset of crack front growth. It was assumed that the ductile fracture in front of the crack starts at the location along the crack front where the accumulated effective plastic strain reaches a critical value. According to numerous research articles, the critical effective plastic strain depends on the stress triaxiality and the Lode angle. The experimental program was performed using five different specimen geometries, three different materials, and three different temperatures of +20 °C, −20 °C, and −50 °C. Using the experimental data and results of the finite element computations, the critical effective plastic strains were determined for each material and temperature. However, before the critical effective plastic strain was determined, a careful calibration of the stress–strain curves was performed after modification of the Bai–Wierzbicki procedure. It was found that critical effective plastic strain was a function of triaxiality factor and Lode parameter, as expected, and that the fracture locus was useful to estimate the onset of ductile crack growth.

Constraint Corrected Cleavage Fracture Assessment Based on Tests of Standard and Small Scale Cruciform Specimens

2009 ◽  
Author(s):  
Jo¨rg Hohe ◽  
Volker Hardenacke ◽  
Dieter Siegele
Keyword(s):  
Numerical Simulation ◽  
Plastic Strain ◽  
Cleavage Fracture ◽  
Crack Front ◽  
Stress Triaxiality ◽  
Local Stress ◽  
Fracture Model ◽  
Additional Stress ◽  
Small Scale ◽  
Fracture Assessment

The objective of the present study is the determination and validation of a constraint corrected probabilistic cleavage fracture model considering both, the nucleation and the possible instability of potentially critical microdefects. For this purpose, the local mechanical conditions at the cleavage triggering point are analyzed by a numerical simulation of different fracture mechanics experiments using C(T), M(T) and SE(B) specimens with deep and shallow cracks. The data base is extended by experiments on novel small scale cruciform bending specimens allowing the application of an additional stress acting longitudinally to the crack front. Based on the results, an enhanced local cleavage fracture model is proposed, which accounts for the nucleation of microdefects in terms of a combined parameter of the local accumulated plastic strain and the local stress triaxiality ratio.

A MODIFIED DUCTILE FRACTURE MODEL INCORPORATING SYNERGISTIC EFFECTS OF PRESSURE AND LODE ANGLE

2012 ◽  
Vol 04 (02) ◽  
pp. 1250022 ◽  
Author(s):  
XUELING FAN ◽  
QIN SUN ◽  
YANJIE LIU
Keyword(s):  
Experimental Data ◽  
Ductile Fracture ◽  
Damage Mechanics ◽  
Synergistic Effects ◽  
Fracture Model ◽  
Ductile Materials ◽  
Fracture Behaviors ◽  
Lode Angle ◽  
Ductile Fracture Model ◽  
Stress Invariant

A modified ductile fracture model is proposed based on continuum damage mechanics and three-stress-invariant criteria. In the modified model, the effects of hydrostatic pressure and Lode angle are considered and combined in the developed fracture envelope. To predict the fracture behaviors of ductile materials, the model is implemented into the commercial finite element platform ABAQUS/Explicit through a user material subroutine VUMAT. The validity of this model is examined by comparing the numerical results with experimental data of round bar and compact tension tests. It is demonstrated that comparing with other three-stress-invariant models the modified ductile fracture model can predict values compare favorably with experimental data especially in the unloading stage. The model can be adopted to predict the fracture patterns and unloading process of ductile materials and thus to investigate the whole range of the elastic-plastic ductile fracture behaviors of materials.

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