ASTM D695 Standard Test Method for Compressive Properties of Rigid Plastics

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The ASTM D695 testing allows plastic manufacturers, compounders, product designers, engineers, suppliers, and quality-control officials to analyze the compression response of a rigid plastic material. The ASTM D695 procedure is appropriate if the compression properties are an important variable in the selection process. ASTM D695 specifies the procedure for characterizing the behavior of a broad range of rigid plastics, from molded to cast to other forms. The procedure provides the stress-strain response of a sample while under an established load profile.

• Material Type: Rigid plastics and suitable rigid plastic compounds. 
• Loading: Applies compressive force along the specimen’s longitudinal axis. 
• Properties Measured: Compressive stress, strain, modulus, yield behavior, and other applicable compressive characteristics. 
• Specimen Geometry: Uses standardized specimen configurations appropriate for compression testing. 
• Test Conditions: Testing is performed under controlled loading and environmental conditions. 
• Deformation Measurement: Records specimen deformation as compressive force increases. 
• Result: Provides quantitative compressive-property data for material evaluation and comparison. 
• Applications: Supports material selection, product development, quality control, and engineering design. 

What are the uses of ASTM D695 testing?

ASTM D695 describes the procedure for determining the compression response of rigid plastics. The data obtained from this test includes an engineering stress/strain curve, which enables engineers to understand stiffness, strength, and deformation of plastics under compression. Common applications include:

• Material characterization of the compressive response of plastics.
• Product development comparing plastic formulations for injection molding or other manufacturing processes.
• Quality control of various production runs.
• Material selection for precast concrete elements or other cases where components are to be subjected to compression.
• Design evaluation to obtain necessary data for engineering purposes.
• Comparison between different plastic types, compounds, or injection molding processing parameters.
• R&D to examine the effect of different additives on plastics.

Which Materials Can Be Tested According to ASTM D695?

ASTM D695 is applicable to rigid plastics that can be prepared into compression test specimens. The material can be unfilled or reinforced depending upon the application and the production of test specimens that meet the requirements of the standard. So the testing can be performed for a wide variety of thermoplastic and thermosetting plastics. Materials may include:

• Rigid Thermoplastics: Such as rigid engineering and structural thermoplastics. 
• Thermosetting Plastics: Rigid plastics formed from thermosetting resin systems. 
• Filled Plastics: Materials containing mineral, particulate, or other fillers. 
• Reinforced Plastics: Rigid plastics reinforced with suitable fibers or other reinforcement. 
• Molded Plastics: Compression or injection-molded rigid plastic materials. 
• Cast Plastics: Rigid cast polymer materials that can be prepared into suitable specimens. 
• Plastic Compounds: Formulations developed for structural or engineering applications. 

Why is ASTM D695 important?

ASTM D695 is significant as most rigid plastic parts are subject to compressive loading in service. Compressive qualities allow engineers to assess whether the test material would be suitable and not deform excessively under applied loads until failure or rupture. Standardized testing allows technicians and analysts to make valid comparisons between multiple materials. The resulting data can support material selection, product design, quality control, and performance evaluation.

ASTM D695 Testing Process and Data Collection

The technician measures the specimen dimensions in mm and conditions the specimens when required. The specimen is then positioned centrally between the compression platens to minimize eccentric loading. The testing machine applies compressive force at the specified rate while the load cell records force and the deformation system measures specimen shortening. The technician records load, deformation, specimen dimensions, test temperature, and other applicable test conditions throughout the test. The analyst uses the measured force and specimen dimensions to calculate compressive stress and other applicable properties. The resulting stress-strain data are evaluated to determine the material’s compressive behavior, including applicable modulus, yield, or strength characteristics.

Common Challenges and Troubleshooting

One common challenge is misalignment of the specimen between the compression platens. Eccentric loading can produce uneven stress distribution and affect the measured compressive properties. Technicians should center and align the specimen carefully before applying the load. Incorrect specimen dimensions can also produce inaccurate stress calculations. Technicians should measure the relevant dimensions with calibrated equipment and use representative specimens prepared according to the applicable requirements. Specimen end surfaces that are not sufficiently flat or parallel can cause uneven loading. Proper specimen preparation and careful inspection of the loading surfaces help improve contact between the specimen and compression platens.

• Compressive results are calculated from the applied force and the original specimen dimensions according to the applicable ASTM D695 procedure. The resulting stress-strain data can be used to evaluate compressive modulus, yield behavior, compressive strength, and other applicable characteristics.
• The technician records specimen identification, material description, specimen dimensions in mm, conditioning information, test temperature, loading conditions, applied force, deformation, and other relevant test conditions.
• The analyst documents measured load and deformation values, calculated compressive stress and strain, stress-strain behavior, applicable modulus or yield values, and other required compressive properties. Compressive stress is generally reported in MPa, while strain and elongation-type deformation are reported as % or as a dimensionless value, as applicable.
• The report contains the specimen identification, material description, specimen dimensions, conditioning information, test conditions, load measurements, deformation measurements, calculated compressive properties, and applicable observations.
• Consistent specimen preparation, dimensional measurement, specimen alignment, controlled loading, deformation measurement, equipment calibration, and data calculation allow technicians and analysts to provide reliable and comparable ASTM D695 results.

Link to ASTM D695