The mechanical properties of materials mainly include:
Elastic properties, plastic properties, hardness and impact resistance, etc.
In the early stage of product design, linear analysis can be performed first to understand the general trend. In the later stage, it is necessary to balance safety and economy. At this time, it is necessary to analyze the material in depth and consider nonlinear analysis. For assemblies, sometimes it is necessary to consider the contact between components, such as slippage, separation, etc. The bending of thin plates will cause great deformation and stress using linear analysis. In fact, after considering geometric nonlinearity, its deformation is much smaller than linear analysis. The maximum stress is close to the yield stress, the displacement is abnormally large, and the two surfaces penetrate each other. Nonlinear analysis is relatively complex and takes a lot of time to master.
Stiffness:
The ability of a material to resist elastic deformation when subjected to force. The size of the stiffness depends on the geometry of the component and the elastic modulus of the material.
Strength:
The ability of a material to resist plastic deformation and fracture under the action of external force or the ability of a component to resist fracture or residual deformation exceeding the allowable limit after bearing load.
Plastic deformation:
Deformation that cannot be restored to its original shape and size after the external force is removed is called plastic deformation.
Common strength indicators include tensile strength and yield strength, and the experimental methods are as follows.
Tensile test-tensile strength, yield strength. Three-point bending test-bending strength. Compression test-compressive strength.
Yield strength:
When the load is small, the material can return to its original state after unloading, and the material is in the elastic region; when the load exceeds a certain value, the material cannot return to its original state after unloading, and the material is in the plastic region. The transition point between the elastic region and the plastic region is the yield point, and the stress at the yield point is the yield stress. In the elastic region, the stress-strain relationship is linear, but in the plastic region, the stress-strain relationship is nonlinear.
Elastic modulus:
Under normal circumstances, the deformation of an object in which the force is proportional to the length change is called elastic deformation, and its ratio is the elastic modulus. More strictly defined, within the elastic range, the slope of the stress-strain curve is the elastic modulus.
Tensile strength:
After the yield stage, the material regains its ability to resist deformation. If it continues to deform, the force must be increased. This stage is the strengthening stage of the material. The stress corresponding to the highest point in the strengthening stage is the tensile strength. The stress that causes the material to break is the fracture stress. In the tensile test of the material, there is usually a necking phenomenon, and the cross-section of the material will continue to decrease. When drawing the stress-strain curve, if the change in the cross-section of the material is not considered, the resulting curve is called the engineering stress-strain curve; if the influence of the cross-section change is considered, the resulting curve is the real stress-strain curve.
Hardness:
The property of solid materials to resist permanent deformation, the relationship between hardness and strength, generally the higher the strength, the higher the resistance to plastic deformation, the higher the hardness value, and vice versa. Hardness varies according to the test method, including Brinell hardness (HB), Rockwell hardness (HRC), Vickers hardness (HV), Leeb hardness (HL), etc. Among them, Brinell and Rockwell are more commonly used.
Summary:
Strength - tensile and compressive strength (yield strength Rp (MPa) tensile strength Rm (MPa)); stiffness - deformation resistance (elastic modulus E (MPa));
Hardness - wear resistance (Rockwell hardness (HRB));
Toughness - ductility (elongation A (%)).
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