Plastic materials. What are the limit stresses (dangerous stresses) of brittle materials?

The dangerous stress of plastic material is yield strength;
The dangerous stress of brittle material is tensile limit (tensile strength)

What is the difference between stress-strain curve and force deformation curve?

Different coordinates, different stress and stress, stress = force / cross-sectional area
The difference between strain and deformation is that deformation usually refers to displacement, so the initial length is l, the ending length is l, and the deformation is l-l
Therefore, strain = deformation / initial length, i.e. (l-l.) / L

How many stages is the tensile curve of low carbon steel? The relationship between force and displacement in each stage?

1. Linear elastic deformation stage: when the stress is lower than the elastic limit, the stress is proportional to the deformation of the sample, the stress is removed, and the deformation disappears. 2. Non linear elastic deformation stage: it is still elastic deformation, but the stress is not proportional to the deformation of the sample. 3. Yield stage: when the stress reaches the yield limit, the displacement of the sample increases, but

Don't explain the difference between tensile strength and fracture strength with the tensile curve of low carbon steel

When a material is stretched at a constant speed, the longer it is stretched, the greater the force required. However, when the length exceeds a certain value, the force required to maintain the constant speed will decrease until it breaks. The strength and tensile strength of the maximum force required in this process. The strength and breaking strength at break

The fracture shapes of low carbon steel and cast iron were compared, and the mechanical causes of failure were analyzed

The results show that necking occurs when low carbon steel is stretched, the fracture section is smaller than the actual section, the fracture section is uneven, and the fracture is metallic luster

Allowable normal bending stress of 45 steel!

The yield limit of No.45 steel is 360MPa, so the allowable normal stress is 360 divided by the safety factor, which is determined by the actual situation, generally 1.5-2

Error analysis of bending normal stress test of beam
Write down the cause of the error,

1. Inaccurate loading position
2. The load may be inaccurate
3. Anisotropy or heterogeneity of materials

Why the elastic modulus is not used to calculate the theoretical value of normal stress in the experiment of pure bending normal stress of beam
When the material is subjected to bending deformation, it is found from the theoretical formula that it has nothing to do with the elastic modulus of the material, but only with the cross-sectional area. The elastic modulus is not involved in the bending calculation at all. This is the theoretical formula verified in the experiment. The elastic modulus is only used in tension and compression. When the bending theoretical formula is verified, it is obtained from the tension and compression calculation formula. Stress = elastic modulus x strain

Stress = bending moment x distance to neutral layer / interface moment of inertia there is no elastic modulus. The elastic modulus is approximate in derivation. You can see it by reading the book of mechanics of materials

Is the bending normal stress affected by the elastic modulus of the material? Why?

The bending stress is directly proportional to the bending moment and inversely proportional to the section modulus of the member. The section modulus of the member is a shape constant (the shape and size of the section have been determined), so the bending stress has nothing to do with the elastic modulus of the material. The bending deformation is inversely proportional to the product of the elastic modulus of the material and the moment of inertia of the section

If the tensile modulus of elasticity is different from the compressive modulus of elasticity, how will the bending normal stress be distributed

In fact, there are many such structures. Prestressed concrete is that if the lower edge is equipped with more steel bars, the tensile and compressive elastic modulus of the section is not consistent. So you can understand it according to the bending stress distribution of prestressed beams

Plastic materials. What are the limit stresses (dangerous stresses) of brittle materials?