ISO 14126:2023

Overview

ISO 14126:2023 - Fibre-reinforced plastic composites - Determination of compressive properties in the in‑plane direction - specifies standardized test methods for measuring in‑plane compressive properties of fibre‑reinforced plastic (FRP) composites with thermosetting or thermoplastic matrices. The second edition (2023) updates specimen preparation, alignment criteria and adds guidance such as digital image correlation (DIC) recommendations. This standard is intended for specification, quality control and comparative testing of composite laminates and finished/semi‑finished products.

Key technical topics and requirements

• Scope and purpose: Methods cover compressive strength, compressive modulus and failure strain in directions parallel to the plane of lamination. Results are intended for specifications and quality-control purposes.
• Two loading methods:
  • Method 1 - shear loading (gauge length unsupported).
  • Method 2 - combined loading (gauge length unsupported); for tabbed specimens load transfer is a mix of end‑loading and shear‑loading through tabs.
• Two specimen designs:
  • Type A - fixed thickness, end‑tabbed; mainly for aerospace‑style preimpregnates (≈0.125 mm ply thickness), used for unidirectional or biaxial reinforcement with aligned continuous or long (>7.5 mm) discontinuous fibres.
  • Type B - range of thicknesses, untabbed or end‑tabbed, two sizes (B1, B2), used for multidirectional, mat, fabric and coarser fibre architectures.
• Specimen preparation and dimensions: The standard specifies required specimen dimensions and preparation practices (Annex B normative). Tests on non‑specified dimensions or conditions can produce non‑comparable results.
• Alignment and fixtures: Includes criteria for alignment of specimen and loading train (Annex A) and allows different anti‑buckling/support fixtures provided bending is limited to acceptable levels.
• Validation and failure criteria: Guidance to check that method/specimen combination produces valid, representative failures; warns that different combinations may yield different results.
• Measurement and analysis: Requirements for test machine calibration, strain measurement, calculation of compressive strength, modulus and failure strain, and statistical reporting (including precision and significant figures).
• Additional guidance: Annexes provide Euler buckling criteria, predicted tab length, and informative guidance for DIC strain and bending measurements.

Practical applications and users

ISO 14126 is used by:

• Materials and mechanical engineers conducting composite compression testing
• Test laboratories, certification bodies and quality‑control teams
• Aerospace, automotive, marine and sports manufacturers specifying in‑plane compressive performance
• R&D teams comparing layups, resin systems and reinforcement formats

Benefits include comparable, repeatable compressive property data for design, acceptance and failure analysis.

Related standards

• ISO 20975‑1 - through‑thickness compression properties
• ISO 604 - compression testing of rigid plastics (short/unaligned fibres)
• ISO 291, ISO 1268, ISO 7500‑1, ISO 9513 - referenced normative documents for conditioning, specimen production and machine calibration

Keywords: ISO 14126, in‑plane compression testing, fibre‑reinforced plastic composites, compressive properties, Type A specimen, Type B specimen, Method 1, Method 2, composite compression test, DIC guidance.