Classical Material Mechanics test questions

First, fill in the blanks (1 points, total 28 points)

1. The material mechanics takes the member as the research object, mainly studies its strength, the rigidity, the stability question in the tensile compression, the shearing, the torsion, the bending these four kinds of basic deformation, in order to ensure the design is both economical and safe rod piece.

2. The basic method of finding internal force in material mechanics is the cross section method, which requires four steps, and the four step is to cut one knife, take a section, add internal force, and balance the column.

3. Axial tensile compression deformation, the internal force of its section is called the Axial Force, torsional deformation, the internal force of the section is called torque; when pure bending, the internal force of the section is called the bending moment, and the internal force of the cross section is shear and bending moment when the transverse force is bent.

4. The elongation is greater than or equal to 5% of the material, called plastic material, less than 5% of the material, called brittle material.

5. Poisson's ratio is the absolute value of the ratio of transverse strain to longitudinal strain, which is a constant for general materials.

6. When calculating the internal force of a section, it is assumed that the internal force of the section is positive direction. The square direction of the axial force is that the outer normal of the section is positive, the square of the torque is positive for the outer normal of the section, and the square direction of the shear force is the clockwise rotation of the micro-section, and the square direction of the bending moment is to make the micro-section concave positive.

Two Judgment question (2 points per question, 20 points total)

1. For the convenience of research, the total stress is usually decomposed into two directions, the stress perpendicular to the section is called Shear stress, and the stress in the section is called the positive stress. (X)

2. Within the range of elasticity, Hooke's laws are applicable. (X)

3. Whether the rod is subjected to external forces, the internal force is universal, it is actually a cross-sectional force between the molecules. (X)

4. The translation theorem of forces in theoretical mechanics can be used directly in material mechanics. (X)

5. There can be no bending moment on the two simply supported ends of simply supported beams. (X)

6. Stress is the average internal force of the cross section. (X)

7. Because the component is a deformed solid, in the study of the balance of components, should be calculated according to the size after deformation. (X)

8. Material mechanics is limited to the study of straight bars of the same section. (X)

9. The task of material mechanics is to make the components as safe as possible. (X)

10. When the cross section method is used to find the internal force, the balance can be calculated by preserving any part of the member after the cut-off. (√)

Three Drawing brief question (12 points)

The stress-strain curves of low carbon steels are plotted, several key points are marked, and the names and characteristics of several stages of stretching are briefly described.

Solution: Tensile stress-strain curves for low carbon steels are as follows

The OB segment----the elastic phase. As long as the tensile force is removed, the deformation of the specimen will disappear completely.

The BC segment----yielding phase. This phase of stress remains constant, but the strain increases significantly and the deformation is not recoverable.

CE segment----hardening phase. This phase of material restores the ability to resist deformation and must be increased in order to deform it.

The EF segment----The local deformation stage. In a certain local range, the transverse dimension suddenly shrinks sharply. To the F point is pulled off.

Four. Calculation questions (40 points)

1. One axis force as shown, try to draw its axis diagram (8 points)

Solution: Use the Fast method (left plus right minus) to get the Axis force diagram as follows

2, known: a propeller shaft, n =200r/min, the active wheel input p1=80kw, the output of the follower p2=25kw,p3=35kw,p4=20kw, as shown in Figure 2-2, the test drawing torque diagram. (12 points)

Solution: First calculate the external force dipole moment

Then use the Fast method (left plus right minus) to draw the torque graph

3. Draw the diagram of the shearing force and bending moment of the beam below. (12 points)

Solution: First, the binding is calculated.

Then the shear force diagram and the bending moment are plotted by the fast method.

4, the figure shows the effect of the end of the curved tube f=3kn concentrated force, try to find 1-1 section of internal force. (8 points)

Solution: First Use the section method, then select the right half section, and make the following diagram

According to the equilibrium column equation of the Space Force system

Solution to