ISO 75-1:2020

Overview

ISO 75-1:2020 - Plastics - Determination of temperature of deflection under load - Part 1: General test method defines the general procedure for measuring the temperature of deflection under load (commonly called Heat Deflection Temperature or HDT) of plastics using three‑point bending. The standard specifies the principle, apparatus, specimen handling and test procedure for obtaining the temperature at which a defined deflection (corresponding to a specified flexural strain increase) occurs as temperature is raised at a controlled rate.

Key points from the scope:

• Covers general test method for flexural stress under three‑point loading.
• Provides specimen types and constant loads to suit different materials.
• Clarifies the method is for comparative assessment at elevated temperature - not for predicting actual end‑use performance.
• Identifies ISO 75-2 and ISO 75-3 as parts that give material‑specific requirements.

Key Topics

• Test principle: Three‑point bending with constant load while temperature is increased until the standard deflection is reached.
• Apparatus: Rigid frame with supports and a loading edge; deflection and temperature measuring instruments; calibrated weights to achieve required flexural stress.
• Heating media: Heating bath (liquid), fluidized bed or air oven. Liquid methods (e.g., silicone oil) are the reference when needed.
• Temperature control: Specified heating rate of (120 ± 10) °C/h (equivalent to 12 ± 1 °C per 6 min). Temperature sensor must be within 12.5 mm of the loading point and not touch the specimen.
• Specimens: Preferred dimensions are given; specific spans and loads are referenced to ISO 75-2/75-3 for different materials.
• Corrections and precision: Blank (reference) tests to correct for apparatus thermal expansion; support and loading edge radii are specified (3.0 ± 0.2 mm).
• Limitations: Results are comparative; true comparability requires materials with the same room‑temperature flexural modulus. Data are not intended for design analysis or endurance prediction.

Applications

Who uses ISO 75-1:2020 and why:

• Materials laboratories & testing services: Routine HDT/HDT testing for quality control and material data sheets.
• Plastics manufacturers & compounders: Compare formulations, evaluate heat resistance and processing effects.
• R&D and material selection teams: Rank candidate polymers, filled plastics and short‑fibre composites for elevated‑temperature applications.
• Compliance and procurement specialists: Verify supplier data and perform comparative benchmarking.

Note: Use ISO 75-2 or ISO 75-3 when testing specific classes of plastics (filled/fibre‑reinforced or long‑fibre/laminates).

Related Standards

• ISO 75-2 - Plastics and ebonite (material‑specific requirements)
• ISO 75-3 - High‑strength thermosetting laminates and long‑fibre‑reinforced plastics
• ISO 291 - Standard atmospheres for conditioning and testing
• ISO 16012 - Determination of linear dimensions of test specimens
• IEC 60584-1, IEC 60751 - Thermocouple and RTD specifications

Keywords: ISO 75-1:2020, HDT, heat deflection temperature, plastics testing, temperature of deflection under load, three-point bending, flexural stress.