1. Home
2. All Testing
3. Density-Related
4. Density

Density Testing of Materials

Significance and Purpose

Density Testing determines the mass per unit volume of a material under specified conditions. Density influences mechanical, thermal, and processing characteristics and is crucial for material selection, quality control, and performance evaluation across industries such as automotive, aerospace, packaging, construction, and electronics.

Density testing is fundamental for:

• Material Characterization: Distinguishing between materials with similar compositions but different structures.
• Process Control: Ensuring consistency in manufacturing.
• Performance Prediction: Relating density to mechanical, thermal, and electrical performance.
• Quality Assurance: Detecting defects like voids, inclusions, or porosity.
• Regulatory Compliance: Meeting standards for product certification.

Different types of density testing address material states and applications:

• Solid Density: Mass per unit volume of a solid (ASTM D792, ISO 1183).
• Melt Density: Density of molten materials during processing (ASTM D3835).
• Bulk Density: Density of materials in loose, granular, or powdered form (ASTM D1895).

Relevant ASTM and ISO Standards

• ASTM D792 / ISO 1183: Solid Density of Plastics by Displacement.
• ASTM D3835: Melt Density of Polymeric Materials via Capillary Rheometry.
• ASTM D1895-96: Bulk Density of Plastics in Granular or Powder Form.

These standards define procedures, conditions, and measurement techniques to ensure accurate, repeatable results.

DatapointLabs Tests for Density Testing

Tests in the DatapointLabs test catalog that reference density testing are as follows:

General Density Testing (inquire regarding material suitability)

Test ID	Test Description	Standards
D-010	Solid Density	ASTM D792, ISO 1183
D-015	Melt Density	ASTM D3835
D-016	Bulk Density	ASTM D1895-96

Principle of Operation

Density is defined as the ratio of mass to volume. Different methods are employed depending on the material state:

1. Solid Density (ASTM D792, ISO 1183):
   • Measured using Archimedes’ principle (buoyancy method).
   • The mass of a specimen is measured in air and in a liquid of known density (e.g., water or ethanol).
2. Melt Density (ASTM D3835):
   • Measured using a capillary rheometer during material flow.
   • As the material is extruded through a die, melt density is calculated based on the volume displacement and mass flow rate.
3. Bulk Density (ASTM D1895):
   • Measured by filling a graduated container with granular or powdered material and measuring the mass.
   • Provides insights into packing behavior, flowability, and material consistency.

Typical Procedure

Solid Density (ASTM D792 / ISO 1183)

1. Sample Preparation:
   • Cut the specimen into a regular shape.
   • Ensure it is free from surface defects or voids.
2. Measurement Setup:
   • Use a precision balance with a density determination kit.
   • Record the mass in air (m_a) and then in a liquid of known density (m_w).
3. Density Calculation:
   $$\mathrm{\rho }=\frac{{\mathrm{m}}_{\mathrm{a}}}{{\mathrm{m}}_{\mathrm{a}}-{\mathrm{m}}_{\mathrm{w}}}.{\mathrm{\rho }}_{\mathrm{liquid}}$$
   where:
   • ρ = solid density
   • m_a = mass in air
   • m_w = mass in liquid
   • ρ_liquid = density of the immersion liquid
4. Correction for Buoyancy Effects:
   • Apply corrections for materials that absorb the immersion liquid or contain entrapped air.

Melt Density (ASTM D3835)

1. Sample Preparation:
   • Load polymer granules into a capillary rheometer.
2. Test Setup:
   • Heat the material to the processing temperature.
   • Apply a constant piston speed to extrude the molten polymer.
3. Data Collection:
   • Measure the mass flow rate (ṁ) and volume flow rate (V̇).
4. Density Calculation:
   ${\mathrm{\rho }}_{\mathrm{melt}}=\frac{\dot{\mathrm{m}}}{\dot{\mathrm{V}}}$
   where:
   • ρ_melt = melt density
   • ṁ = mass flow rate
   • V̇ = volume flow rate

Bulk Density (ASTM D1895-96)

1. Sample Preparation:
   • Pour a known mass of granular, powdered, or flaky material into a cylindrical container of known volume.
2. Test Execution:
   • Fill the container without tapping or compressing the material.
   • Level the surface and weigh the container with the material.
3. Density Calculation:
   ${\mathrm{\rho }}_{\mathrm{bulk}}=\frac{\mathrm{m}}{\mathrm{V}}$
   where:
   • ρ_bulk = bulk density
   • m = mass of the material
   • V = volume of the container
4. Variations for Specific Materials:
   • For materials prone to segregation or compaction, perform tests under different loading conditions.

Specimen Types

Specimens used by DatapointLabs in density testing are as follows:

Specimen Type	DatapointLabs Test IDs
Parts, Any Shape [Details]	D-010
Pellets [Details]	D-015, D-016

Characterization Measurements

Solid Density (ASTM D792, ISO 1183)

• Solid Density: Mass per unit volume of the solid material at room temperature.

Melt Density (ASTM D3835)

• Melt Density: Mass per unit volume of molten polymer during extrusion.

Bulk Density (ASTM D1895-96)

• Bulk Density: Density of a granular or powdered material in its uncompacted state.

Typical Data Reported (see test descriptions for exact details)

• Solid Density: Measured under standard conditions.
• Melt Density: At specified processing temperature.
• Bulk Density: For materials in granular or powder form.
• Temperature and Pressure Conditions: For melt density measurements.
• Material Absorption Characteristics: When immersion fluids are involved.

Suitable Material Types

• Plastics: Thermoplastics, thermosets, and fiber-reinforced composites.
• Metals: Aluminum, steel, and alloys.
• Ceramics and Glasses: Dense and porous materials.
• Elastomers: Rubber and thermoplastic elastomers.
• Foams: Open- and closed-cell foams.
• Granular and Powdered Materials: Polymers, ceramics, and powdered metals.

Suitable Applications

• Plastics Industry: Ensuring consistency for injection molding and extrusion processes.
• Aerospace and Automotive: Weight reduction through density optimization.
• Medical Devices: Controlling material density for implants and prosthetics.
• Construction Materials: Evaluating density and porosity of composites.
• Packaging: Lightweight materials for improved transport efficiency.
• Metal Powder Production: Quality control for additive manufacturing powders.

Conclusion

Density testing is a fundamental material characterization technique with applications in quality control, product development, and material selection. By applying standardized methods like ASTM D792, ASTM D3835, ASTM D189, and  ISO 1183, engineers and researchers can accurately assess solid, melt, and bulk density for various materials. This information is critical for optimizing mechanical performance, ensuring process consistency, and predicting product behavior under different operational conditions.