Hardness testing is a mechanical property test that measures a material's resistance to localized deformation (such as indentation, scratching, penetration, etc.). Its core principle involves applying force to a material surface using a specific indenter under a defined load, and characterizing the material's "hardness" based on the degree of surface deformation (e.g., indentation size, depth). It is one of the most commonly used tests in material property evaluation and is widely applied to quality control and performance analysis of various materials including metals, plastics, rubber, ceramics, coatings, and more.

Core Principle

Hardness essentially reflects the strength of interatomic/intermolecular bonding forces within a material: the stronger the bonding forces, the more difficult the material is to deform, and the higher its hardness. During testing, a standardized indenter (such as a steel ball, diamond cone, or diamond pyramid) is brought into contact with the material surface under a specified load, held for a certain dwell time, and then removed. The diameter, depth, or diagonal length of the resulting indentation is measured, and the hardness value is calculated using a formula (which varies by method).

Common Test Methods and Applicable Scenarios

Depending on the material hardness range, characteristics, and testing requirements, common methods can be divided into two categories: primarily for metallic materials and primarily for non-metallic materials, as detailed below:

I. Common Methods for Metals and Hard Materials

1. Brinell Hardness (HB)

  • Principle: A cemented carbide ball (or steel ball) with a diameter of 1–10 mm is pressed into the material surface under a high load (250–3000 kgf). After holding for a specified time, the indentation diameter is measured, and the hardness value is calculated using a formula (unit: HBW, for cemented carbide ball).

  • Applicable Materials: Metals with lower hardness (e.g., low-carbon steel, cast iron, copper alloys, aluminum alloys), or materials with relatively rough surfaces (accommodating larger indentations).

  • Advantages: Large indentation, highly representative result (reflects the overall hardness of the material);

  • Disadvantages: The indentation damages the sample, unsuitable for thin materials or precision parts.

  • Standards: GB/T 231.1, ISO 6506-1, ASTM E10.

2. Rockwell Hardness (HR)

  • Principle: A diamond cone (120° apex angle) or a steel ball (1.588 mm diameter) is used as the indenter. A preliminary load (10 kgf) is applied first, followed by a main load (60/100/150 kgf). After unloading, the hardness value is calculated from the difference in indentation depth.

  • Characteristics: Uses multiple "scales" corresponding to different indenters and loads, covering different hardness ranges:

    • HRC: Diamond cone + 150 kgf, suitable for high-hardness materials (e.g., quenched steel, tool steel, hardness 20–70 HRC);

    • HRB: Steel ball + 100 kgf, suitable for medium-to-low hardness materials (e.g., mild steel, copper alloys, 20–100 HRB);

    • HRA: Diamond cone + 60 kgf, suitable for ultra-hard materials (e.g., cemented carbide, 20–88 HRA).

  • Advantages: Small indentation (minimal sample damage), fast testing speed, suitable for batch inspection;

  • Disadvantages: Small indentation yields lower representativeness (multiple measurements with averaging are needed).

  • Standards: GB/T 230.1, ISO 6508-1, ASTM E18.

3. Vickers Hardness (HV)

  • Principle: A square-based diamond pyramid (136° apex angle) is used as the indenter, pressed into the material under a low load (1–120 kgf). The diagonal length of the indentation is measured, and the hardness value is calculated using a formula (unit: HV).

  • Applicable Materials: Thin materials (e.g., sheet metal, coatings), high-hardness materials (e.g., ceramics, cemented carbide), precision parts (e.g., gear tooth surfaces).

  • Advantages: Wide load range (can test materials from extremely soft to extremely hard), high precision, results under different loads are directly comparable (no scale differences);

  • Disadvantages: Low testing efficiency (requires diagonal measurement, suited for precision laboratory testing).

  • Standards: GB/T 4340.1, ISO 6507-1, ASTM E92.

4. Leeb Hardness (HL)

  • Principle: An impact body (with a diamond-tipped indenter) strikes the material surface at a fixed velocity. The rebound velocity is measured to calculate the hardness value (HL), which can be converted to other hardness values such as HB, HR, etc.

  • Applicable Scenarios: On-site testing of large workpieces (e.g., machine tool guideways, pressure vessels) without sampling (portable).

  • Standards: GB/T 17394, ISO 16859, ASTM A956.

II. Common Methods for Non-Metallic Materials

1. Shore Hardness (HS)

  • Principle: A specifically shaped indenter pin (conical or flat) is pressed into the material under spring force. Hardness is determined based on penetration depth, using two common scales:

    • Shore A (HA): Suitable for soft materials (e.g., rubber, foam, soft plastics, hardness 0–100 HA);

    • Shore D (HD): Suitable for hard materials (e.g., rigid plastics, nylon, PVC, hardness 0–100 HD).

  • Advantages: Simple to operate, portable, suitable for on-site rapid inspection;

  • Standards: GB/T 2411, ISO 868, ASTM D2240.

2. Knoop Hardness (HK)

  • Principle: An elongated rhombic diamond indenter (long/short diagonal ratio ≈7:1) is pressed into the material under a low load, and the long diagonal length is measured to calculate hardness (unit: HK).

  • Applicable Materials: Extremely hard and extremely thin materials (e.g., ceramics, glass, metal foils, coatings), with shallow indentation (minimal sample damage).

  • Standards: GB/T 18449.1, ISO 4545, ASTM E384.

Key Influencing Factors

The accuracy of test results depends on controlling the following parameters:


  • Indenter Type: Steel balls (soft materials) and diamond (hard materials) must be matched to the material hardness (to prevent indenter deformation);

  • Load Magnitude: Excessive load may penetrate through thin materials, while insufficient load yields indistinct indentations (select based on material thickness);

  • Sample Condition: The surface must be flat and free of oxide layers/oil contamination (otherwise abnormal indentations may result);

  • Dwell Time: The load holding time (typically 10–30 s) affects the adequacy of plastic deformation (especially for high-temperature materials or plastics).

Significance of Testing

  • Performance Evaluation: Hardness is positively correlated with material strength (e.g., tensile strength) and wear resistance (e.g., high-hardness steel is more wear-resistant);

  • Quality Control: Verify heat treatment effectiveness (e.g., HRC value of quenched steel must meet requirements) and material consistency (hardness deviation of parts within the same batch must fall within range);

  • Material Selection Reference: Select materials with matching hardness based on application scenarios (e.g., gears require high hardness for wear resistance, gaskets require low hardness for sealing).


For testing protocols tailored to specific materials (e.g., aluminum alloys, rubber, ceramics), further details can be provided to refine the method and parameters.