What is rate independent plasticity?
Rate-independent plasticity is characterized by the irreversible straining that occurs in a material once a certain level of stress is reached. The plastic strains are assumed to develop instantaneously, that is, independent of time.
How do you calculate plastic strain rate?
1 Answer
- T = Cauchy stress tensor.
- T0=T−13tr(T)1 = Deviatoric part of Cauchy stress.
- ˉσ=√23T0:T0 = Equivalent tensile stress.
- Np=√32T0ˉσ = Direction of plastic flow (assume co-directionality)
- E=Ee+Ep = Additive strain decomposition.
- T=C:Ee=(2G)Ee+λtr(Ee)1 = Linearized Elasticity constitutive equation.
- ˙Ep=√32˙ˉϵpNp.
What is perfect plasticity?
Perfect plasticity is a property of materials to undergo irreversible deformation without any increase in stresses or loads. Plastic materials that have been hardened by prior deformation, such as cold forming, may need increasingly higher stresses to deform further.
What is true for perfect plasticity in terms of yield stress and strain?
The concept of perfect plasticity is associated with the mechanical behaviour of materials that while yielding do not present a further increase of stress for an increase in strain (i.e. a plateau is observed in two dimensions, cf.
What is a rate independent material?
A rate independent material, at least in the concept of hypo-elasticity is one which is a homogeneous of degree one function in the rate of deformation.
What does rate dependent mean?
Rate dependence is a well-known behavioral phenomenon, in which change in responding following an intervention is dependent upon the baseline rate of behavior. Rate dependence was first demonstrated when baseline responding was maintained by different schedules of reinforcement.
What is plastic strain ratio?
Plastic strain ratio r is a measure of the ability of a sheet metal to resist thinning or thickening when subjected to a tensile or compressive force. It is typically advantageous if the material reduces in area a minimal amount when subject to this force, meaning a good drawing material has a high r value.
How do you calculate strain rate sensitivity?
parameter m = (∂ lnσ/∂ ln ˙ε)T,ε is the strain rate sensitivity.
What are the yield criteria for plasticity?
Abstract. A yield condition or yield criterion describes a material failure in structural plasticity. It defines the threshold state of a material between elastic and plastic or brittle failure deformations. It is very important to a dopt a proper yield criterion in the design of a structure.
What is plasticity measured in?
Measuring of plasticity is based on the principle of impact deformation using a sample with a defined diameter and height deformed by a free falling plate with a given mass. It is defined as the ratio between the water responsible of tile contraction and the total water; Bigot curves show this information.
How much plastic strain is acceptable?
It is stated that due to material considerations a permanent/plastic strain up to 2% is allowable without any testing.
What is Johnson Cook material model?
The Johnson-Cook model is a plasticity model that is based on Mises plasticity with closed-form analytical equations specifying the hardening behavior and the strain-rate dependence of the yield stress.
What is r value and n value?
n-value indicates material work hardening under plastic deformation, while the r-value indicates the vertical anisotropy. The n-value is determined by tensile stress and strain values; while for the r-value calculation the specimen section measurement is also required.
What does strain rate sensitivity mean?
Strain Rate Sensitivity (SRS) measures the change in yield pressure between slow compression speed and production speed.
What is strain rate sensitivity material?
Strain rate sensitivity (SRS) is an important material property because it quantifies the tendency of the material to creep. Materials that do not creep have a near-zero strain rate sensitivity.
What is von Mises and Tresca criteria?
Both Tresca and von Mises criteria are essentially yielding criteria that are typically used to predict an onset of yielding in homogeneous or isotropic ductile metals (Dieter, 1976; Dowling, 1993). Brazed joints, however, are quite far from isotropic.
What is a high plasticity index?
A high PI indicates an excess of clay or colloids in the soil. Its value is zero whenever the PL is greater or equal to the LL. The plasticity index also gives a good indication of compressibility (see Section 10.3). The greater the PI, the greater the soil compressibility.
What is high plasticity?
The process of slope failures in high-plasticity clays involves formation of surface cracks, moisture. infiltration through the cracks into the soil mass, a reduction in suction and hence shearing resistance of the. soil, and ultimately slope failure when the driving stresses exceed the shearing resistance of the soil.
What is the equivalent plastic strain?
The equivalent plastic strain is the integral of the equivalent plastic strain rate, and the equivalent plastic strain rate is dened in terms of the plastic strain rate, Note that there is no prime on the plastic strain rate; the plastic strain rate tensor is deviatoric in this model by construction.