ASTM D7332 – Fastener Pull-Through Resistance of Fiber-Reinforced Polymer Matrix Composites
Fastener pull through resistance of a multidirectional polymer matrix composite reinforced by high-modulus fibers can be measured using the standard test method in ASTM D7332. The force vs displacement response can describe the fastener pull-through resistance. This characteristic is exhibited when mechanical fasteners are pulled through a composite plate, with the force applied perpendicular to the plane of the plate. The materials are limited to continuous-fiber or discontinuous-fiber reinforced composites, such as tape or fabric, where the laminate is symmetric and balanced towards the test direction.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
ASTM D7332 describes test methods for measuring the resistance of fiber-reinforced polymer matrix composite laminates to fastener pull-through failure. Pull-through failure occurs when a fastener head or washer is pulled through the composite, representing a critical failure mode in thin composite structures subjected to through-thickness tensile loads.
This data is required for designing composite joints where out-of-plane loading (normal to the laminate plane) can cause progressive fastener pull-through damage.
Scope, Applications, and Benefits
Scope
ASTM D7332 covers PMC laminates with both protruding-head and countersunk-head fasteners and determines:
- Pull-through failure load
- Load-displacement behavior up to failure
- Fastener geometry and laminate thickness effects
- Washer diameter influence on pull-through strength
Applications
- Aerospace thin skin to substructure attachment joint design
- Automotive composite panel fastening system selection
- Marine composite deck hardware fastening qualification
- Wind turbine blade fastener connection design
- Structural composite inspection access panel fastener sizing
Benefits
- Provides direct pull-through strength data for joint design
- Evaluates both protruding and countersunk fastener head geometries
- Identifies optimal washer diameter for maximum pull-through resistance
- Supports damage tolerance analysis of composite fastened joints
- Small specimen requirement reduces material cost for screening tests
Test Process
Specimen Preparation
Composite panels with drilled holes are fitted with fasteners using specified washers and torque.
1Fixture Setup
Specimens are loaded in a pull-through fixture, applying tension to the fastener head while the panel is supported on a backing plate.
2Pull-Through Loading
Tensile load is applied through the fastener at a controlled rate; load and displacement are continuously recorded until fastener pull-through occurs.
3Data Analysis
Pull-through failure load, absorbed energy, and failure mode are determined from the load-displacement trace.
4Technical Specifications
| Parameter | Details |
|---|---|
| Standard | ASTM D7332 |
| Test Principle | Tensile pull-through of fastener through composite panel |
| Applicable Materials | Continuous fiber PMC laminates |
| Fastener Types | Protruding-head and countersunk-head |
| Support Hole Diameter | As specified (affects constraint conditions) |
| Measured Outputs | Pull-through force (N or lbf), displacement, failure mode |
Instrumentation Used for Testing
- Universal testing machine with appropriate load cell
- Pull-through test fixture with defined support and backing geometry
- Appropriate fasteners, washers, and installation torque wrench
- Displacement transducer or crosshead displacement recording
- Precision calipers for specimen dimension measurement
Results and Deliverables
- Pull-through failure load (N) for each specimen
- Load-displacement curves
- Absorbed energy to failure
- Failure mode documentation (laminate damage zone characterization)
- Statistical summary and design allowable recommendations
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Frequently Asked Questions
Pull-through failure is when the fastener head (or washer) penetrates through the composite laminate thickness under out-of-plane tensile load, creating a hole larger than the fastener diameter and losing joint clamping function.
Thicker laminates generally provide higher pull-through resistance; the relationship is approximately proportional to laminate thickness squared for bearing-type pull-through mechanisms.
Yes — larger washers distribute load over a larger area, significantly increasing pull-through resistance; washer diameter is one of the primary design variables for improving pull-through performance.
Countersunk fasteners generally show lower pull-through resistance because the angled bearing surface concentrates load on a smaller laminate area compared to flat protruding head fasteners.
Yes — local laminate buildup (pad-up) around fastener locations is a common design practice to increase pull-through resistance without increasing overall laminate weight.
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