Indentation Testing Principles & Methodologies
The QualiHRBV™ integrates three standardized indentation mechanics into a single testing platform: depth-differential displacement, spherical impression contact area, and pyramidal diagonal evaluation. This unified setup covers Regular Rockwell, Superficial Rockwell, Brinell, and Vickers disciplines without requiring separate testing frames.
Rockwell & Superficial Rockwell Method (ASTM E18 / ISO 6508)
The Rockwell test measures the permanent depth displacement (e) produced by a major test force relative to a seated preload baseline.
- Preliminary Preload (F0): Applies a minor load (10 kgf for Regular Rockwell; 3 kgf for Superficial Rockwell) to break past surface roughness and establish an exact zero-reference position.
- Major Test Force (F1): Increases the load to the total test force (60 to 150 kgf for Regular; 15 to 45 kgf for Superficial), initiating material penetration.
- Recovery and Depth Measurement: After a programmed dwell time, the major load is released while maintaining the minor preload. The permanent depth difference determines the hardness value:
Formula: HR = E - (e / S)
- E = 100 (diamond cone indenters) or 130 (ball indenters on regular scales).
- S = 0.002 mm (Regular Rockwell: HRA, HRBW, HRC, HRD, HRFW, HRGW).
- S = 0.001 mm (Superficial Rockwell: HR15N, HR30N, HR45N, HR15TW, HR30TW, HR45TW).
- Resolution: 0.1 HR direct digital readout.
Brinell Optical Indentation Method (ASTM E10 / ISO 6506)
The Brinell method calculates hardness by dividing the applied test load by the curved surface area of the spherical crater formed by a sintered tungsten carbide ball indenter (Φ1.588 mm, Φ2.5 mm, or Φ5.0 mm).
Formula: HBW = 0.102 × [2F / (π × D × (D - √(D² - d²)))]
- F = Applied force in Newtons (153.2 N to 1839 N / 15.625 kgf to 187.5 kgf).
- D = Ball diameter in millimeters (1.588 mm, 2.5 mm, 5.0 mm).
- d = Mean impression diameter in millimeters:
(d1 + d2) / 2. - Optical Configuration: 37.5X, 75X, and 150X magnification paths with CCD automated image analysis compatibility across an 8 to 653 HBW range.
Vickers Pyramidal Indentation Method (ASTM E92 / ISO 6507)
The Vickers test uses a square-base diamond pyramid indenter with a 136-degree apex angle. Because the resulting impression remains geometrically similar across all force levels, readings stay consistent across homogeneous materials.
Formula: HV = 0.102 × [2F × sin(136° / 2) / d²] = 1.8544 × (F / d²) [with F in kgf]
- F = Applied test force (5, 10, 20, 30, 50, 100 kgf).
- d = Mean diagonal length in millimeters:
(d1 + d2) / 2. - Range: 5 to 2990 HV (0.1 HV resolution) for case-hardened depths, surface coatings, and weld heat-affected zones.
Method Comparison Matrix
| Test Method | Indenter Type | Applied Test Force | Primary Output Metric | Standard Reference |
|---|
| Regular Rockwell | 120° Diamond Cone / Φ1.588 mm Carbide Ball | 60, 100, 150 kgf (588.4 to 1471 N) | Depth differential (e) at 0.002 mm scale unit | ASTM E18, ISO 6508 |
| Superficial Rockwell | 120° Diamond Cone / Φ1.588 mm Carbide Ball | 15, 30, 45 kgf (147.1 to 441.3 N) | Depth differential (e) at 0.001 mm scale unit | ASTM E18, ISO 6508 |
| Brinell | Carbide Ball (Φ1.588, 2.5, 5.0 mm) | 15.625 to 187.5 kgf (153.2 to 1839 N) | Impression diameter (d = [d1 + d2] / 2) | ASTM E10, ISO 6506 |
| Vickers | 136° Diamond Square Pyramid | 5 to 100 kgf (49.03 to 980.7 N) | Diagonal span (d = [d1 + d2] / 2) | ASTM E92, ISO 6507 |
Closed-Loop Force Application Mechanics
Traditional multi-scale hardness testers rely on manual cast-iron weight stacks attached to mechanical levers. Over extended operation, mechanical pivots collect dust, generate friction drag, and produce inertial force spikes upon contact.
The QualiHRBV™ utilizes an electronic closed-loop pressure sensor control system. A load cell mounted inline with the indenter monitors applied force hundreds of times per second to command the micro-stepper motor.
- Controlled Force Application: Eliminates inertial impact spikes as the indenter makes contact with the test sample.
- Active Dwell Regulation: Prevents force relaxation during holding periods (programmable from 1 to 60 seconds).
- Automated Force Selection: Switches between Superficial Rockwell, Regular Rockwell, Vickers, and Brinell force targets via touchscreen selection.
Indentation Corrections & Geometry Offsets
Calculating accurate material hardness requires correcting for external physical factors and workpiece geometry:
- Frame Compliance Compensation: Structural frames experience minute elastic deflection under high loads (up to 187.5 kgf). The onboard software isolates true indentation depth (hc) by canceling frame movement:
hc = hmeasured - (Cf × F). - Creep Kinetics Stabilization: Ductile materials continue plastic displacement while holding peak load. The electronic feedback loop maintains constant force throughout the dwell window until the deformation rate stabilizes.
- Indenter Tip Offsets: Diamond penetrators feature a slight microscopic radius at the apex. The calculation algorithms incorporate verified tip geometry to keep shallow-depth readings consistent.
- Curvature Corrections (ASTM E18 / ISO 6508): Cylindrical and spherical surfaces alter lateral material constraint. Integrated correction algorithms adjust raw values based on the component's radius of curvature.
Cross-Scale Hardness Conversion (ASTM E140 / ISO 18265)
Converting hardness values across Rockwell, Brinell, and Vickers requires verified empirical data because stress distributions under a spherical indenter differ from those under a sharp diamond pyramid.
The QualiHRBV™ features built-in conversion algorithms based on ASTM E140 and ISO 18265 standards. The system displays converted equivalent scales in real time while preserving primary, directly measured raw data for laboratory quality audit trails.
