The difference between stiffness, strength and hardness

CAEThe concepts of stiffness, strength and hardness are often mentioned in structural simulation. So what is the difference between these three?

In fact, stiffness, strength and hardness are indicators of the mechanical properties (or mechanical properties) of the material. It is related to the deformation of the object. The deformation of objects is generally divided into elastic deformation and plastic deformation. Elastic deformation - deformation that can be restored to its original shape and size after external force is removed. Plastic deformation - deformation that cannot be restored to its original shape and size after external force is removed.

Stiffness - The ability of metal materials to resist elastic deformation when subjected to stress.

Strength - The ability of metal materials to resist plastic deformation and fracture under external forces.

Hardness - The ability of metal materials to resist harder objects being pressed into them.

There is no necessary connection between the three, but hardness is a comprehensive mechanical performance indicator. Generally, materials with relatively hardness have relatively higher strength.

The ability of metal materials to resist permanent deformation and fracture under external forces is called strength. According to the nature of external forces, the main ones are yield strength, tensile strength, compressive strength, bending strength, etc. The commonly used engineering is yield strength and tensile strength. These two strength indicators can be measured through tensile tests. Strength refers to the ability of a part to resist breakage or residual deformation exceeding the allowable limit after being subjected to load. In other words, strength is an important indicator for measuring the load-bearing capacity of the part itself (i.e., resistance to failure). Strength is the basic requirement that mechanical parts should meet first. The strength of mechanical parts can generally be divided into static strength, fatigue strength (bending fatigue and contact fatigue, etc.), fracture strength, impact strength, mild and low temperature strength, strength and creep under corrosion conditions, glue strength and other items. The experimental research on strength is a comprehensive study, mainly through its stress state to study the stress conditions of parts and predict the conditions and timing of failure.

The ability of a material to partially resist the pressing of a hard object into its surface is called hardness. The more common method of testing steel hardness is to use a file to file and wipe the edge of the workpiece.,The depth of scratches on its surface is used to determine the lower hardness of its hardness. This method is called the filing method. This method is not very scientific. Use a hardness tester to test it more accurately,It is a common method for testing hardness in modern times. Commonly used hardness measurement methods include Brinell hardness, Rockwell hardness and Vickers hardness. Hardness is an important performance indicator for measuring the hardness and hardness of metal materials. It can be understood as the ability of a material to resist elastic deformation, plastic deformation or damage, or it can also be expressed as the ability of a material to resist residual deformation and counter-destruction. Hardness is not a simple physical concept, but a comprehensive indicator of the mechanical properties of materials such as elasticity, plasticity, strength and toughness. Hardness test can be divided into static pressing methods (such as Brinell hardness, Rockwell hardness, Vickers hardness, etc.), scratching methods (such as Mohs hardness), jumping methods (such as Shore hardness), microhardness, temperature hardness, etc., according to their different testing methods: Hardness, strength, stiffness, and plasticity are the main mechanical properties commonly referred to as, and there are also elasticity, impact toughness, fatigue strength and fracture toughness. To understand their differences, we must first understand the relevant concepts:

1, Hardness: The ability of metal materials to resist harder objects being pressed into them. Hardness is an important performance indicator for measuring the hardness and hardness of metal materials. It can be understood as the ability of a material to resist elastic deformation, plastic deformation or damage, or it can also be expressed as the ability of a material to resist residual deformation and counter-destruction. Hardness test can be divided into static pressing methods (such as Brinell hardness, Rockwell hardness, Vickers hardness, etc.), scratching methods (such as Mohs hardness), jumping methods (such as Shore hardness), microhardness, temperature hardness, etc., according to their different testing methods:

2、Stiffness refers to the ability of a part to resist elastic deformation under load. The stiffness (or rigidity) of a part is often expressed by unit deformation or torque. The magnitude of the stiffness depends on the geometry of the part and the type of material (i.e., the elastic modulus of the material). The stiffness requirement is particularly important for parts that will affect the working quality of the machine after the elastic deformation exceeds a certain value, such as the spindle, guide rail, lead screw, etc. of the machine tool.

3、Typical indicators of strength are yield strengthRp0.2(MPa)and tensile strengthRm(MPa), The typical index of stiffness is elastic modulusAnd (MPa), The typical indicator of hardness is Rockwell hardnessHRB。