scholarly journals Influence of matrix characteristics on fracture toughness of high volume fraction Al2O3/Al–AlN composites

2000 ◽  
Vol 15 (5) ◽  
pp. 1145-1153 ◽  
Author(s):  
N. Nagendra ◽  
V. Jayaram
Keyword(s):  
Heat Treatment ◽  
Fracture Toughness ◽  
Steady State ◽  
Crack Growth ◽  
Volume Fraction ◽  
Void Nucleation ◽  
Matrix Composition ◽  
Al Alloy ◽  
Constraint Factor ◽  
The Matrix

The role of matrix microstructure on the fracture of Al-alloy composites with 60 vol% alumina particulates was studied. The matrix composition and microstructure were systematically varied by changing the infiltration temperature and heat treatment. Characterization was carried out by a combination of metallography, hardness measurements, and fracture studies conducted on compact tension specimens to study the fracture toughness and crack growth in the composites. The composites showed a rise in crack resistance with crack extension (R curves) due to bridges of intact matrix ligaments formed in the crack wake. The steady-state or plateau toughness reached upon stable crack growth was observed to be more sensitive to the process temperature rather than to the heat treatment. Fracture in the composites was predominantly by particle fracture, extensive deformation, and void nucleation in the matrix. Void nucleation occurred in the matrix in the as-solutionized and peak-aged conditions and preferentially near the interface in the underaged and overaged conditions. Micromechanical models based on crack bridging by intact ductile ligaments were modified by a plastic constraint factor from estimates of the plastic zone formed under indentations, and are shown to be adequate in predicting the steady-state toughness of the composite.

Effect of Heat Treatment on Fracture during Bending in AA6016 Aluminium Alloy Sheets

2011 ◽  
Vol 488-489 ◽  
pp. 521-524
Author(s):  
Aleksandar Davidkov ◽  
Roumen H. Petrov ◽  
Peter De Smet ◽  
Leo Kestens
Keyword(s):  
Heat Treatment ◽  
Grain Boundary ◽  
Volume Fraction ◽  
Boundary Structure ◽  
Homogeneous Distribution ◽  
Fracture Mechanisms ◽  
Al Alloy ◽  
Technological Parameters ◽  
The Matrix ◽  
Strengthening Phases

The bending properties of high strength precipitation-hardening AA6016-type Al alloy thin sheets in pre-aged T4P temper state were studied in this work. Microstructural features like grain boundary particles distribution and volume fraction of the matrix strengthening phases were considered as factors controlling the mechanical properties and the fracture of this grade. Remarkable decrease in ductility, accompanied by severe deterioration of bendability occurred when coarse precipitates were found into the grain boundaries. The in-situ fracture sequence investigations as well as the post-failure surfaces observations indicated that grain boundary ductile fracture mechanisms were involved in the propagation of the cracks during bending. Heat treatment simulations were carried out and the results showed that the precise control of the technological parameters during production of these sheets is the key factor responsible for obtaining an appropriate combination of strength and bendability. Only by providing both, homogeneous distribution of the matrix strengthening phases and a favourable grain boundary structure, the severe and often contradictory requirements for the functional properties of these alloys can be successfully satisfied.

scholarly journals On the micromechanism of inclusion driven ductile fracture and its implications on fracture toughness

2020 ◽  
Author(s):  
Yu Liu ◽  
Xinzhu Zheng ◽  
shmuel osovski ◽  
Ankit Srivastava
Keyword(s):  
Fracture Toughness ◽  
Ductile Fracture ◽  
Crack Growth ◽  
Volume Fraction ◽  
Void Nucleation ◽  
Small Scale ◽  
Crack Advance ◽  
Crack Growth Behavior ◽  
Ductile Crack ◽  
Material Parameters

The objective is to identify the micromechanism(s) of ductile crack advance, and isolatethe key microstructural and material parameters that a?ect these micromechanisms andfracture toughness of ductile structural materials. Three dimensional, ?nite element, ?nitedeformation, small scale yielding calculations of mode I crack growth are carried out forductile material matrix containing two populations of void nucleating particles using anelasto-viscoplastic constitutive framework for progressively cavitating solid. The larger par-ticles or inclusions that result in void nucleation at an early stage are modeled discretelywhile smaller particles that require large strains to nucleate voids are homogeneously dis-tributed. The size, spacing and volume fraction of inclusions introduce microstructure-basedlength-scales. In the calculations, ductile crack growth is computed and fracture toughness ischaracterized. Several features of crack growth behavior and dependence of fracture tough-ness on microstructural and material parameters observed in experiments, naturally emergein our calculations. The extent to which the microstructural and material parameters a?ectthe micromechanisms of ductile crack advance and, hence, the macroscopic fracture tough-ness of the material is discussed. The results presented provide guidelines for microstructuralengineering to increase ductile fracture toughness, for example, the results show that for amaterial with small inclusions, increasing the mean inclusion spacing has a greater e?ect onfracture toughness than for a material with large inclusions.

Effects of particle size, particle volume fraction and matrix composition on the fatigue crack growth resistance of Al alloy/Al alloy + SiCp bimaterials

2002 ◽  
Vol 216 (4) ◽  
pp. 245-255
Author(s):  
M T Milan ◽  
P Bowen
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Crack Growth Resistance ◽  
Matrix Composition ◽  
Al Alloy ◽  
Particle Volume ◽  
Fatigue Crack Growth Resistance

The fatigue crack growth resistance of Al alloy/Al alloy + SiCp bimaterials for crack growth perpendicular to the interface is affected by thermal residual stresses, elastic mismatch, plastic mismatch and direction of crack approach to the interface. When the crack approaches the interface from the composite side, the crack growth resistance is mainly controlled by the compressive residual stress near to the interface. Conversely, when the crack grows from the aluminium side towards the composite, the crack is shielded primarily by the elastic/plastic mismatch. In this work, the effects of particle size, particle volume fraction and matrix composition on the fatigue crack growth resistance of Al alloy/Al alloy + SiCp bimaterials have been assessed. These parameters can affect both the thermal residual stress profile and the elastic/plastic mismatch, and hence the effective crack tip driving force for crack extension is also affected.

Fracture and R-curves in high volume fraction Al2O3/Al composites

2000 ◽  
Vol 15 (5) ◽  
pp. 1131-1144 ◽  
Author(s):  
N. Nagendra ◽  
V. Jayaram
Keyword(s):  
Fracture Toughness ◽  
Volume Fraction ◽  
Porous Alumina ◽  
Crack Tip ◽  
High Volume ◽  
Fracture Mechanisms ◽  
Constraint Factor ◽  
Ductile Phase ◽  
Crack Bridging ◽  
The Matrix

Fracture toughness and fracture mechanisms in Al2O3/Al composites are described. The unique flexibility offered by pressureless infiltration of molten Al alloys into porous alumina preforms was utilized to investigate the effect of microstructural scale and matrix properties on the fracture toughness and the shape of the crack resistance curves (R-curves). The results indicate that the observed increment in toughness is due to crack bridging by intact matrix ligaments behind the crack tip. The deformation behavior of the matrix, which is shown to be dependent on the microstructural constraints, is the key parameter that influences both the steady-state toughness and the shape of the R-curves. Previously proposed models based on crack bridging by intact ductile particles in a ceramic matrix have been modified by the inclusion of an experimentally determined plastic constraint factor (P) that determines the deformation of the ductile phase and are shown to be adequate in predicting the toughness increment in the composites. Micromechanical models to predict the crack tip profile and the bridge lengths (L) correlate well with the observed behavior and indicate that the composites can be classified as (i) short-range toughened and (ii) long-range toughened on the basis of their microstructural characteristics.

scholarly journals Iron-chromium-carbon-vanadium white cast irons: Microstructure and properties

2014 ◽  
Vol 68 (4) ◽  
pp. 413-427 ◽  
Author(s):  
Mirjana Filipovic
Keyword(s):  
Fracture Toughness ◽  
Strain Hardening ◽  
Volume Fraction ◽  
Dynamic Fracture Toughness ◽  
M23c6 Carbide ◽  
Cast Irons ◽  
Repeated Impact ◽  
Secondary Carbides ◽  
The Matrix ◽  
Microstructure Parameters

The as-cast microstructure of Fe-Cr-C-V white irons consists of M7C3 and vanadium rich M6C5 carbides in austenitic matrix. Vanadium changed the microstructure parameters of phase present in the structure of these alloys, including volume fraction, size and morphology. The degree of martensitic transformation also depended on the content of vanadium in the alloy. The volume fraction of the carbide phase, carbide size and distribution has an important influence on the wear resistance of Fe-Cr-C-V white irons under low-stress abrasion conditions. However, the dynamic fracture toughness of Fe-Cr-C-V irons is determined mainly by the properties of the matrix. The austenite is more effective in this respect than martensite. Since the austenite in these alloys contained very fine M23C6 carbide particles, higher fracture toughness was attributed to a strengthening of the austenite during fracture. Besides, the secondary carbides which precipitate in the matrix regions also influence the abrasion behaviour. By increasing the matrix strength through a dispersion hardening effect, the fine secondary carbides can increase the mechanical support of the carbides. Deformation and appropriate strain hardening occur in the retained austenite of Fe-Cr-C-V alloys under repeated impact loading. The particles of precipitated M23C6 secondary carbides disturb dislocations movement and contribute to increase the effects of strain hardening in Fe-Cr-C-V white irons.

Loading Rate Effect on Translaminar Fracture Toughness of Hybrid Composite Laminate

2000 ◽  
Author(s):  
Paul Moy ◽  
Jerome Tzeng
Keyword(s):  
Fracture Toughness ◽  
Composite Laminates ◽  
Glass Matrix ◽  
Small Volume ◽  
Loading Rate ◽  
Volume Fraction ◽  
Rate Effect ◽  
The Matrix ◽  
Small Volume Fraction ◽  
Matrix Property

Abstract Fracture toughness properties of composite laminates were evaluated at a loading rate commonly observed in ordinance applications. The laminates are composed of IM7 graphite and a small volume fraction of S2 glass plies to form a cross-ply laminate. Fracture toughness appears to be very rate sensitive if the crack growth perpendicular to the plane dominated by glass/matrix property. Experimental data shows a 30–40% increase of fracture toughness for various layup as the loading rate was increase by 1000 times. The specimens examined under microscopic indicates the strengthening might due to different failure mechanism in the matrix. In addition, there is no visible rate effect if the crack propagation is perpendicular to the graphite dominant plane.

scholarly journals Effect of Crack Bridging on the Toughening of Ceramic/Graphene Composites

2018 ◽  
Vol 57 (1) ◽  
pp. 54-62 ◽  
Author(s):  
S.V. Bobylev ◽  
A.G. Sheinerman
Keyword(s):  
Experimental Data ◽  
Fracture Toughness ◽  
Crack Growth ◽  
Crack Deflection ◽  
Yttria Stabilized Zirconia ◽  
Stabilized Zirconia ◽  
Crack Bridging ◽  
The Matrix ◽  
Graphene Content ◽  
Graphene Platelets

Abstract A model is proposed describing the effect of crack bridging on the fracture toughness of ceramic/graphene composites. The dependences of the fracture toughness on the graphene content and the sizes of the graphene platelets are calculated in the exemplary case of yttria stabilized zirconia (YSZ)/graphene composites. The calculations predict that if crack bridging prevails over crack deflection during crack growth, the maximum toughening can be achieved in the case of long graphene platelets provided that the latter do not rupture and adhere well to the matrix. The model shows good correlation with the experimental data at low graphene concentrations.

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