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Fracture mechanics by three-dimensional crack-tip synchrotron X-ray microscopy.

Withers PJ - Philos Trans A Math Phys Eng Sci (2015)

Bottom Line: To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping.X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces.It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement.

View Article: PubMed Central - PubMed

Affiliation: Manchester X-ray Imaging Facility, School of Materials, Manchester University, Manchester M13 9PL, UK Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0FA, UK p.j.withers@manchester.ac.uk.

ABSTRACT
To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. Conventionally, these are undertaken on separate synchrotron beamlines; however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Finally, further opportunities for synchrotron X-ray microscopy are explored.

No MeSH data available.


Related in: MedlinePlus

Fibre bridging stresses for the SiC fibres bridging a fatigue crack in a Ti–6Al–4V/35% SiC long-fibre composite holding the crack shut at Kmax (filled symbols, continuous lines) and propping it open at Kmin (open symbols, dashed curves). The far-field thermal contraction mismatch residual stresses in the fibres are represented by the horizontal dashed line. (After [50].) (Online version in colour.)
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RSTA20130157F10: Fibre bridging stresses for the SiC fibres bridging a fatigue crack in a Ti–6Al–4V/35% SiC long-fibre composite holding the crack shut at Kmax (filled symbols, continuous lines) and propping it open at Kmin (open symbols, dashed curves). The far-field thermal contraction mismatch residual stresses in the fibres are represented by the horizontal dashed line. (After [50].) (Online version in colour.)

Mentions: While closure stresses act to keep cracks open at Kmin, ligaments that bridge the crack can help to hold a crack shut at Kmax thereby reducing the cyclic amplitude (ΔKeff) experienced by the crack tip. Such crack-face tractions can also be evaluated by diffraction. This is well illustrated by the role of bridging fibres in shielding a fatigue crack in long-fibre composites. The bridging stresses have been quantified by high-resolution synchrotron diffraction for Ti–6Al–4V/35% SCS-6 SiC fibre composite [49]. The bridging stresses in the fibres are shown in figure 10. The crack-face tractions arising from the bridging fibres are around 300 MPa at maximum load. Interestingly, they are compressive (approx. −100 MPa) at Kmin which tends to prop open the crack. This is partly due to the fact that the bridging fibres are pulled out somewhat at Kmax and partly due to the original compressive thermal residual stresses in the fibres. Using a weight function approach, it is possible to calculate the shielding effect of the crack-closing stresses at Kmax and the crack-opening stresses at Kmin. These are shown in §5b and act to greatly reduce the stress intensity range experienced by the crack as more and more fibres bridge the growing crack.Figure 10.


Fracture mechanics by three-dimensional crack-tip synchrotron X-ray microscopy.

Withers PJ - Philos Trans A Math Phys Eng Sci (2015)

Fibre bridging stresses for the SiC fibres bridging a fatigue crack in a Ti–6Al–4V/35% SiC long-fibre composite holding the crack shut at Kmax (filled symbols, continuous lines) and propping it open at Kmin (open symbols, dashed curves). The far-field thermal contraction mismatch residual stresses in the fibres are represented by the horizontal dashed line. (After [50].) (Online version in colour.)
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4308984&req=5

RSTA20130157F10: Fibre bridging stresses for the SiC fibres bridging a fatigue crack in a Ti–6Al–4V/35% SiC long-fibre composite holding the crack shut at Kmax (filled symbols, continuous lines) and propping it open at Kmin (open symbols, dashed curves). The far-field thermal contraction mismatch residual stresses in the fibres are represented by the horizontal dashed line. (After [50].) (Online version in colour.)
Mentions: While closure stresses act to keep cracks open at Kmin, ligaments that bridge the crack can help to hold a crack shut at Kmax thereby reducing the cyclic amplitude (ΔKeff) experienced by the crack tip. Such crack-face tractions can also be evaluated by diffraction. This is well illustrated by the role of bridging fibres in shielding a fatigue crack in long-fibre composites. The bridging stresses have been quantified by high-resolution synchrotron diffraction for Ti–6Al–4V/35% SCS-6 SiC fibre composite [49]. The bridging stresses in the fibres are shown in figure 10. The crack-face tractions arising from the bridging fibres are around 300 MPa at maximum load. Interestingly, they are compressive (approx. −100 MPa) at Kmin which tends to prop open the crack. This is partly due to the fact that the bridging fibres are pulled out somewhat at Kmax and partly due to the original compressive thermal residual stresses in the fibres. Using a weight function approach, it is possible to calculate the shielding effect of the crack-closing stresses at Kmax and the crack-opening stresses at Kmin. These are shown in §5b and act to greatly reduce the stress intensity range experienced by the crack as more and more fibres bridge the growing crack.Figure 10.

Bottom Line: To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping.X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces.It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement.

View Article: PubMed Central - PubMed

Affiliation: Manchester X-ray Imaging Facility, School of Materials, Manchester University, Manchester M13 9PL, UK Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0FA, UK p.j.withers@manchester.ac.uk.

ABSTRACT
To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. Conventionally, these are undertaken on separate synchrotron beamlines; however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Finally, further opportunities for synchrotron X-ray microscopy are explored.

No MeSH data available.


Related in: MedlinePlus