A SIZE EFFECT STUDY ON THE SPLITTING CRACK INITIATION AND PROPAGATION IN OFF-AXIS LAYERS OF COMPOSITE LAMINATES

2021 ◽  
Author(s):  
YAO QIAO ◽  
QIWEI ZHANG ◽  
TROY NAKAGAWA ◽  
MARCO SALVIATO
Keyword(s):  
Crack Initiation ◽  
Size Effect ◽  
Fiber Reinforced Polymers ◽  
Structural Behavior ◽  
Crack Initiation And Propagation ◽  
Damage Mechanisms ◽  
Micro Scale ◽  
Morphological Studies ◽  
Initiation And Propagation ◽  
Macro Scale

This work proposes an investigation on size effects in micro-scale splitting crack initiation and propagation and their consequences on the macro-scale structural behavior carbon-fiber reinforced polymers under transverse tension. Towards this goal, size effect tests were experimentally conducted on both notch-free [90]n composites and specimens with different notch types under three-point bending. The mechanical tests were followed by morphological studies to identify the micro-scale damage mechanisms and their evolution. The results clearly show that splitting crack initiation in the transverse direction of composites not only happens at the fiber/matrix interface but also in the matrix. Moreover, the subsequent development of these damage mechanisms can depend on the structure size. This interesting phenomenon inherently leads to size-dependent structural behavior which can be described through Baznt’s Size Effect Laws. This study on the splitting crack initiation and propagation can provide unprecedented information for the calibration and validation of micromechanical models for the damage behavior of fiber composites at the microscale.

scholarly journals Microstructure and Damage Mechanisms in Thermomechanically Treated Si-Solution-Strengthened Spheroidal Graphite Cast Iron

2018 ◽  
Vol 941 ◽  
pp. 583-588
Author(s):  
Surendra Sujakhu ◽  
Sylvie Castagne
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Fatigue Crack Initiation ◽  
Decisive Role ◽  
Spheroidal Graphite ◽  
Crack Initiation And Propagation ◽  
Damage Mechanisms ◽  
Graphite Particles ◽  
Initiation And Propagation ◽  
Structural Applications

Spheroidal Graphite Irons (SGIs) are ductile cast irons with toughness and ductility comparable to those of carbon steel. In particular, high silicon Solution Strengthened Ferritic (SSF) SGIs are developed to provide higher strength with excellent ductility suitable for structural applications. The main characteristics of these materials lie in the graphite particles inclusions whose morphology and count greatly influence the mechanical properties and more specifically the fatigue crack initiation and propagation behaviour of the SGI components. In this work, SGIs specimens have been subjected to various thermomechanical treatments in order to analyse the influence of these treatments on the microstructure of the material. Observations of degenerated forms of graphite particles alongside the spheroidal nodules in the microstructure were then used as a basis for correlation with damage mechanisms at the microscale. In static tensile testing, it was observed that the matrix-nodule interface decohesion and plastic deformation of the ferrite matrix were the dominant damage mechanisms. In separately performed fatigue crack initiation and fatigue crack propagation tests, it was confirmed that the graphite particle shape played a decisive role in crack initiation and propagation. The results of the microstructural characterization have been implemented in a computational model for further study of the influence of the microstructure on the fatigue behaviour of these materials.

Fatigue crack paths and properties in A356-T6 aluminum alloy microstructurally modified by friction stir processing under different conditions

2015 ◽  
Author(s):  
A. Tajiri ◽  
Y. Uematsu ◽  
T. Kakiuchi ◽  
Y. Suzuki
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Crack Initiation ◽  
Friction Stir Processing ◽  
Casting Defects ◽  
Processing Conditions ◽  
Tool Rotational Speed ◽  
Crack Initiation And Propagation ◽  
Friction Stir ◽  
Initiation And Propagation

A356-T6 cast aluminum alloy is a light weight structural material, but fatigue crack initiates and propagates from a casting defect leading to final fracture. Thus it is important to eliminate casting defects. In this study, friction stir processing (FSP) was applied to A356-T6, in which rotating tool with probe and shoulder was plunged into the material and travels along the longitudinal direction to induce severe plastic deformation, resulting in the modification of microstructure. Two different processing conditions with low and high tool rotational speeds were tried and subsequently fully reversed fatigue tests were performed to investigate the effect of processing conditions on the crack initiation and propagation behavior. The fatigue strengths were successfully improved by both conditions due to the elimination of casting defects. But the lower tool rotational speed could further improve fatigue strength than the higher speed. EBSD analyses revealed that the higher tool rotational speed resulted in the severer texture having detrimental effects on fatigue crack initiation and propagation resistances.

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