ISO 21765:2020

Overview

ISO 21765:2020 - Textiles - Determination of fabric deformability by forced mechanical distension - defines an automatic test method to quantify how textile fabrics deform when forced out of their plane. The standard covers continuous-fibre reinforcement textiles as well as woven, knitted, nonwoven and non‑crimp fabrics (including glass rovings and untwisted carbon filament yarns) used for reinforced composite materials. It is not applicable to resin‑impregnated fabrics. The method is suitable for fabrics treated with powder binder and, for multi‑axial non‑crimp fabrics, evaluates fibre orientation and gaps in the uppermost layer only.

Key topics and requirements

• Test principle: Central mechanical distension of a clamped specimen using a rotationally symmetrical deformation body; automatic data capture and image evaluation.
• Apparatus components:
  • specimen holder (retaining ring and fitting body)
  • deformation body (controlled lift to specified deformation levels)
  • overall and detail imaging cameras
  • laser triangulation for out‑of‑plane measurement
• Measured characteristics (examples of required outputs):
  • deformation force acting on the deformation body
  • fibre‑orientation changes, fibre‑angle change and local undulation (via image processing)
  • gaps: width, portion, area and shape between yarns
  • waviness, loop formation and out‑of‑roundness (via laser triangulation and imaging)
  • residual deformation, shearing angle (for woven fabrics), anisotropy and thinning‑out (for nonwovens)
• Specimen preparation and conditioning referenced to standard atmospheres (ISO 139)
• Procedure & evaluation: stepwise insertion, defined test parameters, imaging and automated evaluation algorithms; statistical reporting and test report requirements are specified.

Applications and users

ISO 21765:2020 is practical for:

• composite manufacturers and process engineers assessing fabric behaviour during forming (e.g., liquid composite moulding, upholstery forming)
• textile R&D and materials labs comparing fabric conformability and formability
• quality control and incoming inspection of reinforcement textiles and technical fabrics
• equipment designers developing forming tools and simulation models who need empirical deformability inputs

Benefits include improved process design (reduce defects from fibre reorientation or gaps), objective comparison of fabric variants, and data to validate simulation of three‑dimensional forming.

Related standards

• ISO 139 (standard atmospheres for conditioning and testing) - normative reference for specimen conditioning
• Prepared by ISO/TC 38 (Textiles), useful alongside industry standards for composite processing and textile test methods

Keywords: ISO 21765:2020, fabric deformability, mechanical distension test, textile test method, reinforcement textiles, non‑crimp fabrics, fibre orientation, laser triangulation, image processing.