Tensile proportional limit

High tensile Proportional Limit Stress (PLS) after CMC processing (allows high CMC design stress and high environmental resistance)... 

Ductility A typical tensile stress-strain curve of many ductile plastics is shown in Fig. 2-13. As strain increases, stress initially increases approximately proportionately (from point 0 to point A). For this reason, point A is called the proportional limit of the material. From point 0 to point B, the behavior of the material is purely elastic but beyond point B, the material exhibits an... 

The important tensile modulus (modulus of elasticity) is another property derived from the stress-strain curve. The speed of testing, unless otherwise indicated is 0.2 in./min, with the exception of molded or laminated TS materials in which the speed is 0.05 in./min. The tensile modulus is the ratio of stress to corresponding strain below the proportional limit of a material and is expressed in psi (pounds per square inch) or MPa (mega-Pascal) (Fig. 2-7). 

It may be pointed out that the term yield point is sometimes erroneously used as a synonym for elastic limit and proportional limit As it has been described in the paragraphs above it is actually a phenomenon that occurs in only a very small number of cases in tensile testing. As it has also been observed in the description that graphically and experimentally, it is an anomalous behaviour in which there is a strain occurring with no increase in stress. 

Fig. 21 The cross-section and fracture surface of SA-Tyrannohex. This shows relatively large fracture energy (-2000 J/m2), higher proportional limit (about 120 MPa) and high tensile strength (200 MPa)...

Young s modulus—the ratio of tensile stress to tensile strain below the proportional limit. 

Tensile modulus The ratio of stress to corresponding strain below the proportional limit of the material. Normally expressed in MPa (megapascals). 

A typical stress-strain diagram for a metal is shown in Fig. 11. This metal follows Hook s law up to a proportional limit ox yield strength) of 2 x 109 Pa. The elastic limit, above which the metal undergoes plastic deformation, which is not recoverable when the stress is removed, is close to the proportional limit. The maximum stress that the metal can support is the ultimate strength (or tensile strength) of the metal, which occurs at the maximum extension of the material. 

The effect of the tensile steel reinforcement ratio, p, on the load-deflection and moment-curvature responses of PC beams is shown in Fig. 15. The moment was computed from the applied loads by statics while the corresponding curvature was calculated from the strain distributions. It is noticed that the load-deflection and moment-curvature responses are very similar in terms of shape. In the first stage of loading, a linear relationship existed between the moment (or load) and curvature (or deflection). This proportional limit stage ended with the formation of a major vertical flexural crack and the resulting change in slope and decrease in stiffness. 

Figure 10.3. (a) Tensile and compressive behaviour of small clearwood samples in green and dry conditions PL = proportional limit R = rupture or failure stress. Wood in compression does not rupture suddenly under load but buckles, (b) Geometry of a necked-down tensile specimen. 

In selecting a material for the construction of high pressure reactors a number of factors must lie considered. The more important of these are as follows 1, Ultimate tensile strength 2, proportional limit 3, corrosion resistance 4, workability 5, recrystallization if operating temperatures are to be as high as 500° C. or higher 6, creep stress if the service period is to be long. 

The ratio of tensile stress to corresponding strain below the proportional limit. Many polymers/blends do not obey Hooke s law through out the elastic range but deviate therefrom even at stresses well below the yield stress. However, stress-strain curves almost always show a linear region at low stresses, and a straight line drawn tangent to this portion of the curve permits calculation of tensile modulus. 

Elastic modulus (MPa X 10 ) Proportional limit (MPa) Ultimate tensile strength (MPa) Percent elongation... 

On an S-S curve, there can be a location at which an increase in strain occurs without any increase in stress. This represents the yield point that is also called yield strength or tensile strength at yield. The yield point can also be identified as the proportional limit it is the greatest stress at which the plastic is capable of sustaining an applied load without deviating from the straight line of an S-S curve. 

Many RPs and URPs have a definite tensile modulus of elasticity (E) where deformation is directly proportional to their loads below the proportional limits. Since stress is proportional to load and strain to... 

Figure 7.6 illustrates a typical curve of tensile strain of a material. From the origin O to the point called proportional limit, the stress-strain curve is a straight line. This linear relation between elongation and the axial force causing it was first noticed by Hooke in 1678 and is called Hooke s Law that states that within the proportional limit the stress is directly proportional to the strain or... 

Interface coating Fiber lay-up Fiber volume.% Proportional limit stress, % MPa Proportional limit strain. % Elastic modulus, GPa Ultimate tensile strength, MPa Ultimate tensile strain,%... 

Tensile testing was carried out in air at a displacement rate of 0.02 /minute. Tensile properties of 0/90° cross-ply Nicalon/BN/SiC/BSAS composites, containing 38-40 volume per cent of fibers, at various temperatures are shown [29-31] in Table 4. Above 1100°C, ultimate strength and the proportional limit fall off fairly rapidly, while modulus decreased by -40% from ambient temperature to 1300°C. Nicalon fiber is known to degrade at 1200°C and degradation rate increases with increase in temperature. Presence of residual glassy phase in the matrix would account for the observed decrease in modulus and increase in failure strain at elevated test temperatures. 

C because of the presence of residual glass in the matrix. Tests were started at stress level near the proportional limit. Approximately every 50 hours, the stress was increased by 2 ksi ( 14MPa) until the sample failed. The results [31] are shown in Fig. 8. The composite survived to a stress level of 60% of its ultimate tensile strength. Examination of the fracture surface of the specimen tested at 1100°C/10ksi ( 70 MPa) for 8 h revealed some embrittlement. 

Elastic modulus values were calculated from a mathematical least squares fit on that linear portion of the tensile stress-strain curves that produced a correlation factor of 0.99. Proportional limit stress and strain values were measured at the upper limit of the elastic modulus defined section of the stress-strain curves. 

Table 3 Main properties of tows (failure load F Young s modulus E, strain-to-failurc e, proportional limit Oi, strength Otow. fraction of fibers broken prior to loading y, critical fraction of individual fiber breaks Oc) and single filaments (Welbull modulus m, scale fhetor Oo) extracted from the tensile stress-strain curves.

Table 4 Main features of the tensile behaviour of minicomposites determined from the force-deformation curves (Fj is proportional limit) and from SEM fractography (fiber pull out length Ip, crack spacing distance at saturation d,).

Filament orientation (degrees) Ultimate tensile strength Proportional limit Elastic modulus (1(P psi) Poisson s ratio... 

Comnressive Modulus The ratio of compressive stress to compressive strain below the proportional limit. Theoretically equal to the Young s Modulus determined from tensile... 

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