What is adiabatic shear instability?
Abstract. Adiabatic shear banding (ASB) is a unique dynamic failure mechanism that results in an unpredicted catastrophic failure due to a concentrated shear deformation mode. It is universally considered as a material or structural instability and as such, ASB is hardly controllable or predictable to some extent.
What causes shear bands?
The shear banding is a result of inhomogeneous plastic deformation when all shear plastic strain is concentrated in narrow regions while the rest of the material remains in elastic domain.
What is meant by shear bands?
A shear band (or, more generally, a ‘strain localization’) is a narrow zone of intense shearing strain, usually of plastic nature, developing during severe deformation of ductile materials. As an example, a soil (overconsolidated silty-clay) specimen is shown in Fig. 1, after an axialsymmetric compression test.
Is cold spray a thermal spray process?
While cold spray is technically a subset of thermal spray, its application does not require a combustion process like most thermal spray applications. Cold spray and thermal spray differ in three main ways; process parameters, coating materials and the resulting coating properties.
What is shear banding in polymers?
Shear banding is produced in polymers when they are exposed to compressive stresses. Small stress relieving cracks nucleate within the polymer parallel to the direction of maximum shear stress at an angle of 45°. As the number of shear bands accumulates the overall strain of the material increases.
Why cold spraying is better than thermal spraying?
The big difference is the particle size of the powder that can be sprayed. Cold spray can spray much finer particles, including nanocrystalline powders. Cold spray powders typically have a grain size of 1-50 µm whereas thermal spray powders vary from 10-100 µm depending on the specific thermal spray process.
Why is it called cold spray?
So, compared to conventional thermal spray, where the spray particles are melted or nearly melted during the deposition process, this is a comparatively low temperature spray process technology; hence, the name cold spray.
What is crazing in polymers?
Crazing is the phenomenon that produces a network of fine cracks on the surface of a material, for example in a glaze layer. Crazing frequently precedes fracture in some glassy thermoplastic polymers. As it only takes place under tensile stress, the plane of the crazing corresponds to the stress direction.
What is the difference between strain and shear strain?
Strain is the deformation of a material from stress. It is simply a ratio of the change in length to the original length. Deformations that are applied perpendicular to the cross section are normal strains, while deformations applied parallel to the cross section are shear strains.
What is the difference between shear stress and shear strain?
Shear stress(τ) = Tangential Force/ Resisting cross-sectional Area. Shear strain can be defined as the ratio of deformation to its original length or shape. Here the shear stress directly proportional to the Shear strain within the elastic limit.
Which gas is used in cold spray?
High pressure cold spraying (HPCS) in which the working gas is nitrogen or helium at pressures above 1.5 MPa, a flow rate of more than 2 m3/min, heating power of 18 kW. It is used for spraying pure metal powders with the sizes of 5–50 μm.
What is Deep Freeze spray used for?
Product description. The spray works rapidly like ice, delivering an instant burst of cooling pain relief to the affected or swollen area. Cooling therapy for muscles and joints is well established and recommended by sports physiotherapists and health professionals.
What is the difference between cold and thermal spray?
What is the difference between cracking and crazing?
It’s possible to distinguish between cracking and crazing by pattern (crazing manifests in mostly parallel rows, while cracked paint has a “checkerboard” appearance), whether paint has attached firmly (crazed paint usually achieves firm adhesion) and whether paint is flexible or brittle (crazing can occur in soft paint …
What causes plates to craze?
Glaze crazing or glaze crackle is a network of lines or cracks in the fired glazed surface. It happens when a glaze is under tension. A craze pattern can develop immediately after removal from the kiln or years later.
Is shear strain in radians or degrees?
This shear strain or slide can be defined as the change at a right angle or the angle of deformation. Shear strain is measured in radians and hence has no units.
Which is better Deep Freeze or Deep Heat?
If you have a sprain or strain that is less than 48 hours old, you should avoid using heat rubs or sprays. Hot things increase the blood flow to the area and can cause more damage. Deep Freeze provides a cooling sensation to the area which reduces the blood flow and swelling to the area and helps the healing process.
What are the requirements for adiabatic shear band formation?
However, the fundamental requirement of adiabatic shear band formation is that no heat should be exchanged between the shear band and the surroundings and, as will be seen below, at low temperatures metals and their alloys have a low heat capacity which during deformation promotes high local temperature increases.
What is an example of adiabatic shear?
A particular example that we detail here is that of adiabatic shear bands. Adiabatic shear bands are localized regions of intense shear (which take the form of a band in 2D, of a layer in 3D), where thermo-mechanical coupling effects play a prominent role.
Is adiabatic shear localization a prototype of band-like structures?
Bradley Dodd, Yilong Bai, in Adiabatic Shear Localization (Second Edition), 2012 Now, it appears that adiabatic shear localization is a prototype of band-like structures and is merely a small window in the broad area of localization emerging from a uniform field.
What is the critical strain of adiabatic shear bands?
The timing or critical strain when an adiabatic shear band first nucleates is not a fixed material property, as is sometimes supposed.