The Contribution of Different Fracture Modes on Drilling Delamination Crack Propagation

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Mohammad Reza Vaziri Sereshk ◽  
Hamed Mohammadi Bidhendi
Keyword(s):  
Crack Propagation ◽  
Crack Nucleation ◽  
Dominant Mode ◽  
Mode I ◽  
Minor Effect ◽  
Pure Mode ◽  
Mode Iii ◽  
Major Mode ◽  
Drill Point ◽  
Drilling Conditions

Delamination as the main defect created during drilling of composite laminate is principally a crack nucleation and propagation phenomenon. The fracture-based investigation is performed to identify the significance of different modes involving in this process. The sensitivity analysis is implemented to evaluate magnitude and importance of each mode. As a result, mode I is a dominant mode while drill point removes the material; however, the crack continues to propagate under pure mode III for a while after drilling due to contact of flutes with spalls. This paper investigates the crack formation process for wide variety of drilling conditions and tool geometries. It is demonstrated that although mode III contributes, its minor effect might be neglected if comparing with fracture mode I. Therefore, it may be vanished as a tool design strategy. It is indicated that chisel edge plays a great role in crack propagation under major mode I; therefore, any further design approach which limits or eliminates opening action of chisel edge decreases delamination significantly. Material removal starting from hole perimeter as well as implementing small predrilled holes (such as action of primary cutting lips in step drill) are examined as solutions based on this approach.

Pre-Strain Effects on Mixed-Mode Fatigue Crack Propagation Behaviour of the P355NL1 Pressure Vessels Steel

2018 ◽  
Author(s):  
João Ferreira ◽  
José A. F. O. Correia ◽  
Grzegorz Lesiuk ◽  
Sergio Blasón González ◽  
Maria Cristina R. Gonzalez ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Mixed Mode ◽  
Pressure Vessels ◽  
Mode I ◽  
Pure Mode

Pressure vessels and piping are commonly subjected to plastic deformation during manufacturing or installation. This pre-deformation history, usually called pre-strain, may have a significant influence on the resistance against fatigue crack growth of the material. Several studies have been performed to investigate the pre-strain effects on the pure mode I fatigue crack propagation, but less on mixed-mode (I+II) fatigue crack propagation conditions. The present study aims at investigating the effect of tensile plastic pre-strain on fatigue crack growth behavior (da/dN vs. ΔK) of the P355NL1 pressure vessel steel. For that purpose, fatigue crack propagation tests were conducted on specimens with two distinct degrees of pre-strain: 0% and 6%, under mixed mode (I+II) conditions using CTS specimens. Moreover, for comparison purposes, CT specimens were tested under pure mode I conditions for pre-strains of 0% and 3%. Contrary to the majority of previous studies, that applied plastic deformation directly on the machined specimen, in this work the pre-straining operation was carried out prior to the machining of the specimens with the objective to minimize residual stress effects and distortions. Results revealed that, for the P355NL1 steel, the tensile pre-strain increased fatigue crack initiation angle and reduced fatigue crack growth rates in the Paris region for mixed mode conditions. The pre-straining procedure had a clear impact on the Paris law constants, increasing the coefficient and decreasing the exponent. In the low ΔK region, results indicate that pre-strain causes a decrease in ΔKth.

Damage and Fracture Mechanisms during Mode I and III Loading of Wood

Holzforschung ◽  
2001 ◽  
Vol 55 (5) ◽  
pp. 525-533 ◽  
Author(s):  
E.K. Tschegg ◽  
K. Frühmann ◽  
S.E. Stanzl-Tschegg
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Fracture Energy ◽  
Fracture Mechanisms ◽  
Mode I ◽  
Mode Iii ◽  
Initiation Energy ◽  
Specific Fracture Energy ◽  
Damage And Fracture ◽  
Specific Fracture

Summary Tests under mode I and mode III loading were performed on side grooved Compact-Tension specimens of larch and beech under steady state crack propagation to study the damage and fracture behaviour and the influence of two fibre orientations. From the complete load-displacement diagram, all important damage and fracture mechanical values (stiffness/compliance, microstructural damage, crack initiation energy, specific fracture energy, etc.) have been determined. Crack initiation energy and specific fracture energy are approximately ten times higher for mode III loading than for mode I loading in both wood species. Crack initiation occurs in mode III under external mode III loading, crack propagation, however, takes place under mode I, owing to crack surface interference. The influence of fibre orientation on the (fracture) mechanical properties of beech and larch is different. This difference may be explained mainly by the high number of rays in beech.

A Model for a Propagating Shear Band on the Basis of a Tilt Wall Dislocation Array

1992 ◽  
Vol 45 (3S) ◽  
pp. S71-S74 ◽  
Author(s):  
J. P. Hirth
Keyword(s):  
Shear Band ◽  
Mixed Mode ◽  
Mode I ◽  
Pure Mode ◽  
Rotor Steel ◽  
Mode Iii ◽  
Microstructural Parameters ◽  
Plane Strain Tension ◽  
First Case ◽  
Propagating Shear

Microstructural parameters influencing shear band propagation and, ultimately, fracture in steels are reviewed for two types of test. These are the plane strain tension characteristics of spheroidized steels and the mixed mode I/III J-resistance behavior of a rotor steel. In the former case, shear band propagation is associated with voids forming at carbide particles because of incompatibility effects. In the latter case, the mixed mode I/III toughness is less than that in either pure mode I or pure mode III because local plastic flow in the path of the crack produces damage in the form of voids by a process analogous to the first case. A model for the interaction of a shear band and particles, suggested by these results, is proposed in the form of a discontinuous tilt wall of dislocations that breaks away and propagates past the particles. The model is shown to be consistent with several experimental observations, both of shear band characteristics and of the stress required to propagate the band.

The cellular level mode I fracture behaviour of spruce and birch in the RT crack propagation system

Holzforschung ◽  
2016 ◽  
Vol 70 (2) ◽  
pp. 157-165 ◽  
Author(s):  
Pekka Tukiainen ◽  
Mark Hughes
Keyword(s):  
Crack Propagation ◽  
Fracture Behaviour ◽  
Crack Tip ◽  
Cellular Level ◽  
Image Correlation ◽  
Environmental Scanning ◽  
Mode I ◽  
Microscopic Structure ◽  
Pure Mode ◽  
Displacement Fields

Abstract The effect of the microscopic structure and the moisture content (MC) of wood on its fracture behaviour has been investigated. Green and air-dried spruce (Picea abies [L.] Karst.) and birch (Betula pendula Roth.) wood were subjected to pure mode I loading in the radial- tangential (RT) crack propagation system. Tests were carried out in situ in an environmental scanning electron microscope to observe crack propagation at the cellular level. Crack-tip displacement fields were computed by digital image correlation, and crack propagation was observed from the images captured during testing. Both the MC and the microscopic structure were found to affect the fracture process. In the air-dried birch and spruce, only microcracking caused large displacements ahead of the crack-tip. In spruce, the microcracking zone was larger than in birch. In green birch and spruce, microcracking was less evident than in the air-dried specimens, and in some cases, there were notable deformations in a few cells ahead of the crack-tip before crack extension. Microcracking is considered to be the main toughening mechanism in spruce and birch in the RT crack propagation system.

Fracture Study on Mode I-III Crack of Rock

2006 ◽  
Vol 324-325 ◽  
pp. 1217-1220 ◽  
Author(s):  
Li Yun Li ◽  
Feng Guang Xu ◽  
He Ping Xie ◽  
Wei Ning
Keyword(s):  
Mixed Mode ◽  
Loading Condition ◽  
Fracture Propagation ◽  
Mode I ◽  
Pure Mode ◽  
Mode Iii ◽  
Element Analysis ◽  
Out Of Plane ◽  
Engineering Designs ◽  
Fracture Study

This paper illustrates some preliminary experimental, numerical and theoretical analysis results of mixed mode I-III rock cracks under apparent mode III loading. Some edge notched granite specimens are tested under out-of-plane four-points shearing loading condition, i.e., an apparent mode III loading condition. A series finite element analysis was conducted to understand the mechanism of the crack fracture propagation under this loading condition. The stress intensity factor distributions along the 3-D crack tips are also obtained. All crack fracture propagation surfaces of the specimens are similar helicoids which radius can be mainly influenced by the loading patterns, i.e., the action width s. The crack fracture initiates at the midpoint of the crack front. From the numerical calculation and experimental investigation, it has been revealed that all of these crack fracture initiations are caused by maxima tensile stress σ1. Based on this stress σ1, a new fracture criterion of mixed mode I-III is proposed. Its predictions agree well with the experiment results. This criterion can be applied to practice engineering designs which are related with mixed mode I-III or pure mode III rock crack fracture problems.

Mixed-Mode I/III Fracture Characterization of Aluminum Alloy

2013 ◽  
Vol 853 ◽  
pp. 187-191
Author(s):  
R. Ravichandaran ◽  
G. Thanigaiyarasu
Keyword(s):  
Fracture Toughness ◽  
Aluminum Alloy ◽  
Mixed Mode ◽  
Mode I ◽  
Pure Mode ◽  
Mode Iii ◽  
Fracture Characterization ◽  
Inclination Angles ◽  
Point Bend ◽  
Work Done

Aluminum alloy 5083 is taken for the study of fracture parameters in mixed-mode I/III. Three point bend specimens with load inclination and notch inclination are fabricated and precracked. They are tested with various inclination angles and for two different thicknesses. The results are analyzed and found that the fracture toughness decreases for larger inclination angles. Also, it is found that the thinner specimens are found to be tougher than the thicker specimens. Material and methods Symmetrical three-point bend cracked specimens have been used extensively in fracture mechanics to study mode I fracture properties because they are one of the standard types of specimens used in the ASTM codes for determining the fracture toughness JIc..In the mixed-mode I/III fracture, there is only a limited amount of experimental work done so far. The observations on combined mode I - mode III fracture have been very scarce and there is no general agreement among researchers on the effect of the addition of a mode III component to pure mode I loading. Limited study (Avci et al 2005 [, Kamat and Hirth 1996 [) has been done on bend specimens subjected to mixed-mode I/III when compared to the mode I case, i.e., a center-loaded specimen.

Three-Dimensional Mode Separation to Obtain Stress Intensity Factors

2006 ◽  
Author(s):  
Pei Gu ◽  
R. J. Asaro
Keyword(s):  
Stress Intensity ◽  
Crack Propagation ◽  
Stress Intensity Factors ◽  
Three Dimensional ◽  
Integral Approach ◽  
Mode I ◽  
Mode Ii ◽  
Intensity Factors ◽  
Mode Iii ◽  
Mode Separation

For mixed-mode loading at a crack tip under small-scale yielding condition, mode I, mode II and mode III stress intensity factors control the crack propagation. This paper discusses three-dimensional mode separation to obtain the three stress intensity factors using the interaction integral approach. The 2D interaction integral approach to obtain mode I and mode II stress intensity factors is derived to 3D arbitrary crack configuration for mode I, mode II and mode III stress intensity factors. The method is implemented in a finite element code using domain integral method and numerical examples show good convergence for the domains around the crack tip. A complete solution for the three stress intensity factors is obtained for a bar with inclined crack face to the cross-section from numerical calculations. The solution for the bar is plotted into curves in terms of a set of non-dimensional parameters for practical engineering purpose. From the solution, mode mixity along the crack front and its implication to the direction of crack propagation is discussed.

Experimental Study on Out-Plane Crack Extension in Rimmed Steel

2013 ◽  
Vol 690-693 ◽  
pp. 1767-1770
Author(s):  
Bang Cheng Yang ◽  
Jian Xiong Liu ◽  
Rong Xin Guo ◽  
Hai Ting Xia
Keyword(s):  
Mixed Mode ◽  
Crack Extension ◽  
Thin Sheet ◽  
Mode I ◽  
Pure Mode ◽  
Sheet Metals ◽  
Mode Iii ◽  
Steel Sheets ◽  
Fracture Tests ◽  
Plane Mode

Study on the fractural mechanism of thin sheet metals focuses on how to efficiently fracture and recycle the scrapped vehicles and electrical equipments. By using the experimental fracture mechanics, the failure mode was studied for 10F rimmed steel sheets to be crushed and recycled. In-plane mode I, out-plane mixed mode I /III and mode III fracture tests were conducted under different loading angles. The effects and contributions of mixed mode crack extensions for 10F rimmed steel sheets were analyzed and some sensitive fractural factors were studied. The experimental results show that pure mode III is most viable to fracture the thin sheet 10F rimmed steels.

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