ASTM D6415/D6415M-22

ASTM D6415/D6415M-22 - 1.2.2022

Significance and Use

5.1?Susceptibility to delamination is one of the major design concerns for many advanced laminated composite structures. Complex structural geometries can result in out-of-plane stresses, which may be difficult to analyze. When curved structural details are loaded such that the deformation results in an increase in the radius of curvature, interlaminar tensile stress and delaminations can result. Knowledge of a laminated composite materials resistance to interlaminar fracture is useful for product development and material selection. Failure criteria and design allowables involving out-of-plane stresses may not be readily available or may be poorly validated, requiring additional experimental data.

5.2?This test method can serve the following purposes:

5.2.1?To measure a curved-beam strength;

5.2.2?To measure an interlaminar strength when using a unidirectional specimen where all fibers are oriented 0? relative to the long straight edges of the specimen;

5.2.3?To establish quantitatively the effect of fiber surface treatment, local variations in fiber volume fraction, and processing and environmental variables on the curved beam strength or the interlaminar (through-the-thickness) tensile strength of a particular composite material;

5.2.4?To compare quantitatively the relative curved-beam strength or interlaminar tensile strengths of composite materials with different constituents;

5.2.5?To compare quantitatively the values of the curved-beam strength or interlaminar tensile strengths obtained from different batches of a specific composite material, for example, to use as a material screening criterion, to use for quality assurance, or to develop a design allowable;

5.2.6?To produce out-of-plane structural failure data for structural design and analysis; and

5.2.7?To develop failure criteria for predicting failures caused by out-of-plane stresses.

1. Scope

1.1?This test method determines the curved beam strength of a continuous fiber-reinforced composite material using a 90? curved beam specimen (Figs. 1 and 2). The curved beam consists of two straight legs connected by a 90? bend with a 6.4 mm [0.25 in.] inner radius. An out-of-plane (through-the-thickness) tensile stress is produced in the curved region of the specimen when force is applied. This test method is limited to use with composites consisting of layers of fabric or layers of unidirectional fibers.

FIG. 1?Test Specimen Geometry (SI units)

FIG. 2?Test Specimen Geometry (inch-pound)

1.2?This test method may also be used to measure the interlaminar tensile strength if a unidirectional specimen is used where the fibers run continuously along the legs and around the bend.

1.3?This test method is limited to use with composites consisting of layers of fabric or layers of unidirectional fibers.

1.4?UnitsThe values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.

1.4.1?Within the text, the inch-pound units are shown in brackets.

1.5?This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.6?This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

2. Referenced Documents

E6-25	Standard Terminology Relating to Methods of Mechanical Testing
D792-20	Standard Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement
D883-26	Standard Terminology Relating to Plastics
D3171-22	Standard Test Methods for Constituent Content of Composite Materials
D3878-26	Standard Terminology for Composite Materials
D5229/D5229M-20	Standard Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite Materials
E122-17(2022)	Standard Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or Process
E4-24	Standard Practices for Force Calibration and Verification of Testing Machines
E177-26a	Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods (Includes all amendments and changes 5/14/2026).
E456-13a(2022)e1	Standard Terminology Relating to Quality and Statistics (Includes all amendments and changes 4/16/2024).
E1309-00	Standard Guide for Identification of Fiber-Reinforced Polymer-Matrix Composite Materials in Databases
E1434-00	Standard Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in Databases
E1471-92(1998)	Standard Guide for Identification of Fibers, Fillers, and Core Materials in Computerized Material Property Databases
D5687/D5687M-20	Standard Guide for Preparation of Flat Composite Panels with Processing Guidelines for Specimen Preparation