What Is Scratch?
The scratch test is a test in which scratch resistance is determined by moving a tip of defined geometry across the surface under a constant or increasing load. The result is expressed as a critical load or scratch visibility.
Purpose of Scratch
The purpose is to determine how much the surface resists visible scratch formation during use, and to assess coating-to-substrate adhesion.
Which Products Is Scratch Applied To?
- Automotive interior and exterior trim surfaces
- Paint and varnish systems
- Hard coatings (PVD, DLC)
- Plastic body parts
- Furniture surfaces
In Which Sectors Is Scratch Used?
Standards Related to Scratch
- ISO 1518-1
- ISO 1518-2
- ASTM D7027
- ISO 20502
- ASTM G171
Scratch Conditions
- Tip geometry
- Spherical or diamond tip of the radius defined in the standard
- Load
- Constant load or progressive (increasing) load
- Scratch speed
- Constant rate per the standard
- Environment
- 23 °C ± 2 °C and 50% ± 5 relative humidity
Equipment for Scratch
- Scratch tester
- Calibrated tips
- Optical microscope or confocal profilometer
- Colour/gloss meter (for appearance assessment)
Sample Requirements for Scratch
- The surface must be clean, fully cured and flat
- Coating thickness must be measured and recorded
- The spacing between scratches must conform to the standard
- Generally at least three scratches are applied
Duration of Scratch
The test is short; together with evaluation and microscopic examination, one specimen takes half a working day.
Scratch Procedure
- 1Coating thickness and initial gloss are measured.
- 2The tip and load setup are adjusted per the standard.
- 3A scratch is applied at the defined speed.
- 4The scratch is examined with a microscope; the critical load is determined.
- 5Change in gloss or colour is measured if required.
Scratch Acceptance Criteria
The acceptance criterion is given in the specification as a minimum critical load, or as the absence of a visible scratch at a specified load. Automotive OEM specifications define their own criteria.
Evaluation of Results
Scratch depth, width and coating delamination are evaluated together. The coating opening through to the substrate is recorded as a separate non-conformity.
Scratch Report
- Standard applied
- Tip geometry, load profile and speed
- Coating system and thickness
- Critical load and scratch dimensions
- Microscopic images
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- Automotive OEM surface standards
- Paint and coating specifications
Mekanik Testler — What Does This Testing Field Cover?
The section below describes the field that the Scratch test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Mechanical testing measures how a material or a part behaves under force. The family ranges from static loading (tension, compression, bending) to time-dependent behaviour (fatigue, creep), and from hardness and wear to fracture toughness.
What these tests have in common is that the result is reported as a MATERIAL PROPERTY. Yield strength or hardness is not a conformity decision; it is numerical data against which the design and the product standard will compare. Mechanical test reports are therefore usually an input to an engineering decision rather than to a product approval — material selection, safety factor, life prediction.
The distinction between static and dynamic behaviour is the key to understanding the field. A part may appear entirely unstressed under a static load yet break under repeated loading; fatigue fracture occurs at stresses well below the yield strength and gives no warning. For rotating, vibrating or cyclically loaded parts, a tensile test alone is therefore not sufficient evidence.
Test conditions determine the result, and this is critical for the readability of the report: specimen geometry, loading rate, temperature, conditioning and the gripping arrangement. The same material gives different values under different conditions. In plastics the rate effect is very pronounced, in metals the temperature effect; in composites the specimen orientation changes the result entirely.
Hardness is the most misused measurement in the field. Because it is fast, close to non-destructive and inexpensive, it is often used in place of strength. Conversion tables from hardness to strength exist, but they are APPROXIMATE and depend on the material group; using them as the sole evidence in material acceptance is wrong.
The fracture mechanics side requires a specific competence. Fracture toughness and fatigue crack growth rate measurements make it possible to calculate how long a cracked structure will last; they are the basis of damage-tolerant design in fields such as pressure equipment, aircraft structures and pipelines.
Method groups in this field
Static tests
Tension, compression, bending, shear and torsion. Yield and tensile strength, elongation and modulus of elasticity are obtained.
Impact tests
Charpy and Izod notch impact; the brittle-to-ductile transition behaviour of the material is determined as a function of temperature.
Hardness
Brinell, Vickers, Rockwell, Shore and micro hardness. Valuable for surface treatment depth and local differences in strength.
Fatigue
Force- and strain-controlled axial fatigue, fatigue in bending; S-N curves and the endurance limit.
Creep and stress relaxation
Behaviour under long-term load at high temperature; decisive for boiler, turbine and pressure equipment materials.
Fracture mechanics
Plane-strain fracture toughness, the J integral, CTOD and fatigue crack growth rate.
Wear and friction
Taber and rotating drum abrasion, coefficient of friction measurements.
Commonly confused in this field
- Calculating strength from hardness is approximate; it cannot be used as the sole evidence in material acceptance.
- Adequate static strength does not demonstrate fatigue strength; a cyclically loaded part requires a separate test.
- If test rate and temperature are not reported, the result cannot be compared — especially for polymers and composites.
- A test specimen and the actual part may not give the same value; moulding orientation, weld lines and differences in surface treatment all have an effect.
- A strength value given for a composite without stating the specimen orientation is meaningless.
- ASTM and ISO counterparts measure the same quantity but use different specimen geometries; the results are not treated as directly equivalent.
Which decisions these results support
- Design verification and material selection
- Incoming material control and supplier approval
- Meeting the mechanical requirements of the product standard
- Failure analysis, life prediction and damage tolerance calculation
- Verifying heat treatment and surface treatment processes
Related Tests
Frequently Asked Questions About Scratch
How is a choice made between constant load and increasing load?
Constant load is used when the specification asks whether a scratch occurs at a specific load. Increasing load is preferred to determine the coating's damage-onset threshold (critical load).