What is yield stress

Yield stress fluids are commonly found in many applications, including foods mayonnaise , cosmetics, hygiene shaving creams and toothpaste as well as those common to the drilling industry mud and cement. It has long been observed that drilling fluids do not flow unless subjected to a certain load stress ; that is, they are yield stress materials. Yield stress of a solid is essentially the point at which, when increasing the applied stress, the solid first shows liquid-like behavior of continual deformation.

If this is the case, then we can say that conversely, when decreasing the applied stress, solid-like behavior is first seen—no continual deformation. There has been an ongoing debate in the literature on whether true yield stress fluids exist, and even whether the concept is useful. This is mainly due to the experimental difficulties in determining the yield stress. For example, paint must flow under the brush, but remain fixed in a vertical film despite the force of gravity.

Consumer products such as toothpaste, concrete, food products and even radioactive nuclear waste sludge exhibit yield stresses. The yield stress may serve to keep particulate fillers from settling, as in many consumer products and gelled propellants, or determine whether bubbles remain trapped in cement.

For handling and using these materials, it is paramount to know the stress at which the material starts to flow. An understanding of plastic flow is vital in technology, particularly in the production of large numbers of objects in a variety of complex shapes. The presence of a significant yield stress will impart various qualities to a fluid that may or may not be desirable. A yield stress will often inhibit flow under the relatively low stresses induced by gravity; giving sag and slump resistance to products such as adhesives, plaster, thick-film inks, molten chocolate, paint and fire-retardant coatings.

With some products the presence of a yield stress is not so desirable, leading to, for example, dosing problems in gravity-feed systems or an excess of residue on the sides of inverted bottles. Subscribe to our newsletter to get expert advice and top insights on corrosion science, mitigation and prevention. By: Della Anggabrata. Dictionary Dictionary Term of the Day.

Corrosionpedia Terms. Anodize This: The Brilliance of Anodizing. Top Corrosion Mitigation Technologies to Watch for in Soluble Salts and Coating Performance. Introduction to Electroplating Interview with Jane Debbrecht. Metallizing Whereas, Tensile Strength is the maximum stress that a material can withstand while being stretched or pulled before failing or breaking. The yield strength of a material is determined using a tensile test. The results of the test are plotted on a stress-strain curve.

The stress at the point where the stress-strain curve deviates from proportionality is the yield strength of the material. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible and is known as plastic deformation. The yield strength or yield stress is a material property and is the stress corresponding to the yield point at which the material begins to deform plastically.

Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible. A few materials start to yield, or flow plastically, at a fairly well-defined stress upper yield point that falls rapidly to a lower steady value lower yield point as deformation continues. Any increase in the stress beyond the yield point causes greater permanent deformation and eventually fracture.

The value of yield strength is important in the construction of structures, such that the structures are able to perform in the elastic region under normal servicing conditions. Increasing the concentration of the solute atoms will increase the yield strength of a material, but there is a limit to the amount of solute that can be added, and one should look at the phase diagram for the material and the alloy to make sure that a second phase is not created.

The yield point of a material occurs when the material transitions from elastic behavior — where removing the applied load will return the material to its original shape — to plastic behavior, where deformation is permanent. The yield strength at 0. It is the stress that corresponds to a point at the intersection of a stress-strain curve and a line which is parallel to a specified modulus of elasticity line.

This parallel line is horizontally offset by a predetermined amount. To find yield strength, the predetermined amount of permanent strain is set along the strain axis of the graph, to the right of the origin zero.

It is indicated in Figure 5 as Point D. A straight line is drawn through Point D at the same slope as the initial portion of the stress-strain curve. From this curve we can determine: a the tensile strength, also known as the ultimate tensile strength, the load at failure divided by the original cross sectional area where the ultimate tensile strength U.

Strain is simply the measure of how much an object is stretched or deformed. Strain occurs when force is applied to an object. Strain deals mostly with the change in length of the object. Stress is defined as the force experienced by the object which causes a change in the object while a strain is defined as the change in the shape of an object when stress is applied.

Stress is measurable and has a unit while a strain is a dimensionless quantity and has no unit. Tensile stress is the force exerted per unit cross-sectional area on an object. Tensile strain is the extension per unit original length of an object. The ratio of the elongation to the original length is called a tensile strain and is expressed as follows: See the lower illustration in Fig. A normal stress is a stress that occurs when a member is loaded by an axial force.

The value of the normal force for any prismatic section is simply the force divided by the cross sectional area. A normal stress will occur when a member is placed in tension or compression. The maximum stress occurs at the surface of the beam farthest from the neutral axis. In order to calculate maximum surface stress, you must know the bending moment, the distance from the neutral axis to the outer surface where the maximum stress occurs and the moment of inertia.

Begin typing your search term above and press enter to search. Press ESC to cancel. Skip to content Home What is yield stress formula? Ben Davis May 31,