ASTM D7291 Through-Thickness Flatwise Tensile Strength and Elastic Modulus

ASTM D7291 is used to evaluate Through-Thickness Flatwise Tensile Strength and Elastic Modulus of Fiber-Reinforced Polymer Matrix Composite Materials. Tensile strength is the maximum amount of tensile stress that a material can take until failure.

Talk to an Expert

ASTM D7291 Through-Thickness Flatwise Tensile Strength and Elastic Modulus

TRUSTED BY

Precision-driven testing for dimensional accuracy and compliance

Overview
Scope, Applications, and Benefits
Test Process
Specifications
Instrumentation
Results and Deliverables

Overview

The ASTM D7291 standard is a test method used to evaluate the tensile properties, specifically the flatwise tensile strength and elastic modulus, of polymer matrix composite laminates in the through-thickness direction. This test procedure primarily assesses interlaminar tensile strength and stiffness, which are important parameters for determining laminate delamination resistance.

This test procedure involves loading a flat composite specimen bonded between loading fixtures with a tensile force perpendicular to the laminate surface until failure. The test procedure is used to determine the through-thickness tensile strength and elastic modulus.

Scope, Applications, and Benefits

Scope

ASTM D7291 describes the method for determining the through-thickness (flatwise) tensile strength and elastic modulus of polymer matrix composite laminates. The test involves tensile loading in a direction perpendicular to the laminate surface.

Measures through-thickness tensile strength.
Determines the flatwise elastic modulus.
Applicable to polymer matrix composites.
Defines specimen bonding and loading method.

Applications

Delamination resistance evaluation.
Material qualification testing.
Quality control in composite manufacturing.
Structural design validation.

Benefits

Assesses interlaminar strength directly.
Provides reliable thickness-direction data.
Supports safe composite design.
Enables standardized comparison of materials.

Test Process

Specimen Preparation

Prepare a flat composite specimen to the specified dimensions and ensure that the bonding surfaces are parallel.

Bonding to Fixtures

Bond the specimen between the loading blocks using a suitable adhesive and allow it to cure properly.

Through-Thickness Loading

Apply tensile load perpendicular to the laminate plane until failure, while recording load and displacement

Data Analysis & Reporting

Calculate through-thickness tensile strength and elastic modulus as per ASTM International.

Technical Specifications

Parameter	Details
Material Type	Polymer matrix composite laminates
Loading Direction	Perpendicular to the laminate plane
Specimen Types	Flat, parallel-sided coupon
Bonding Method	Adhesively bonded to loading fixtures
Strain Measurement	Based on displacement over thickness
Testing Machine	Calibrated Universal Testing Machine (UTM)
Loading Mode	Uniaxial tensile loading
Failure Mode	Interlaminar fracture or adhesive failure

Instrumentation Used for Testing

Universal Testing Machine (UTM)
Load Cell
Bonded Loading Fixtures (Steel/Aluminum Blocks)
Alignment Fixtures
Crosshead Displacement Indicator
Data Acquisition System (DAQ)
Adhesive Bonding Materials
Vernier Caliper / Micrometer

Results and Deliverables

Tensile Strength (Through-Thickness)
Through-Thickness Elastic Modulus
Load vs. Displacement Data
Failure Mode Classification
Complete Test Report as per ASTM standard

Why Choose Infinita Lab for ASTM D7291?

At the core of this breadth is our network of 2,000+ accredited labs in the USA, offering access to over 10,000 test types. From advanced metrology (SEM, TEM, RBS, XPS) to mechanical, dielectric, environmental, and standardized ASTM/ISO testing, we give clients unmatched flexibility, specialization, and scale. You’re not limited by geography, facility, or methodology—Infinita connects you to the right testing, every time.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090 to learn more about our services and how we can support you. Request a Quote

Frequently Asked Questions

ASTM D7291 determines the flatwise tensile strength of a composite by pulling it in a direction perpendicular to its laminate layers, testing the bonding strength of the resin system that holds the layers of the composite material together.

Through-thickness strength is the criterion for delamination resistance during out-of-plane loading. Layer separation due to weak interlayer bonding can be a problem in composites subjected to pressure, bending, or more complex loading conditions.

ASTM D7291 is demanded in aerospace, marine, wind energy, and defense applications where thick laminates or sandwich structures are required to resist delamination and retain structural integrity under multidirectional service loads.

ASTM D7291 uses circular or square composite specimens bonded to metal loading blocks. Adhesive bonding ensures uniform load transfer, allowing accurate measurement of flatwise tensile properties without inducing edge-related failure modes.

Flatwise tensile strength is a measure of maximum stress before layer separation, while flatwise elastic modulus is a measure of stiffness. These properties can be used for structural modeling and finite element analysis of laminated composite components.