The ability of a metal material to resist permanent deformation and fracture under external forces is called strength. According to the nature of external force, there are mainly yield strength, tensile strength, compressive strength, bending strength, etc., engineering is commonly used is the yield strength and tensile strength, these two strength indicators can be measured by tensile test
Strength refers to the ability of a part to resist fracture or residual deformation exceeding allowable limits after being subjected to load. That is to say, strength is an important index to measure the bearing capacity of parts themselves (that is, the ability to resist failure). Strength is the basic requirement that mechanical parts should meet first. The strength of mechanical parts can be generally divided into static strength, fatigue strength (bending fatigue and contact fatigue, etc.), fracture strength, impact strength, high temperature and low temperature strength, strength and creep under corrosion conditions, adhesive strength and other items. The strength test is a comprehensive study, mainly through its stress state to study the stress state of parts and predict the failure conditions and opportunities.
(1) Compressive strength — the ability of the material to withstand pressure.
(2) Tensile strength — the ability of the material to withstand tension.
(3) bending strength — the ability of the material to bear the external force caused by bending.
(4) Shear strength — the ability of the material to withstand shear force.
The local resistance of a material to hard material pressing into its surface is called hardness. As early as 1822, Friedrich Mohs proposed a scale of 10 minerals to measure the hardest and softest objects in the world, known as the Mohs durometer. They are divided into ten grades according to how hard or soft they are:
1) talc 2) gypsum 3) calcite 4) fluorite 5) apatite6) orthoclase 7) quartz 8) topaz 9) corundum 10) diamond
The most common way to test the hardness of steel is to use a file on the edge of the workpiece and determine its hardness by the depth of the scratches on the surface. It’s called filing and it’s not very scientific. Hardness testing machine to test more accurate, is the modern test hardness commonly used method. The commonly used hardness testing methods are Brinell hardness, Rockwell hardness and Vickers hardness testing methods
Hardness is an important performance index to measure the degree of softness and hardness of metal materials. It can be understood as the ability of material to resist elastic deformation, plastic deformation or damage, and can also be expressed as the ability of material to resist residual deformation and anti-damage. Hardness is not a simple physical concept, but a comprehensive index of mechanical properties of materials such as elasticity, plasticity, strength and toughness. Hardness test can be divided into static pressure method (such as Brinell hardness, Rockwell hardness, Vickers hardness, etc.), scratch method (such as Mohs hardness), rebound method (such as Shore hardness) and micro hardness, high temperature hardness and other methods.
Brinell hardness is HB[N(KGF /mm2)] (HBS\HBW) (refer to GB/T231-1984). Brinell hardness method is commonly used in production to determine the hardness of annealed, normalized and tempered steel, cast iron, non-ferrous metals, low alloy structural steel and other raw or semi-finished products.
Rockwell hardness can be divided into HRA, HRB, HRC, HRD four, their measurement range and application range is also different. HRC is the most commonly used in general production. Indentation is small, can measure the hardness of thinner materials and hard materials and finished parts.