Short answer

When designing composite structures with holes, consider the use of fasteners not just for assembly but as a means to improve overall stress distribution and reduce sensitivity to layup variations.

Field: Final Production
Source: PolyPublie (École Polytechnique de Montréal) (2020)
Method: Experimental and Analytical
Evidence: Strong effect

Introducing fasteners into composite plates with holes effectively redistributes stress, making the material's stacking sequence less critical for performance. This final production research insight is drawn from a 2020 study published in PolyPublie (École Polytechnique de Montréal). Using Experimental and analytical, researchers explored how this design variable affects real-world outcomes. The key design takeaway: When designing composite structures with holes, consider the use of fasteners not just for assembly but as a means to improve overall stress distribution and reduce sensitivity to layup variations.

Study

Final ProductionHigh ImpactStrong effect

Hole-filling fasteners significantly equalize stress distribution in composite laminates, negating stacking sequence effects.

Introducing fasteners into composite plates with holes effectively redistributes stress, making the material's stacking sequence less critical for performance.

PolyPublie (École Polytechnique de Montréal) · 2020

Key Findings

01Open-hole cross-ply composites with thinner layups exhibited better stress distribution capabilities than thicker ones.
02Open-hole quasi-isotropic composites with thicker layups showed better stress distribution than thinner ones.
03When holes were filled with fasteners, the stress distribution capabilities of cross-ply and quasi-isotropic laminates became nearly equal, diminishing the impact of stacking sequence.
04The Point Stress Criterion (PSC) provided a very good approximation of the Stress Concentration Factor (SCF).

Application

Design takeaway

When designing composite structures with holes, consider the use of fasteners not just for assembly but as a means to improve overall stress distribution and reduce sensitivity to layup variations.

How to apply

When designing bolted or riveted joints in composite panels, analyze the stress concentration around the holes and consider how the fastener's presence and fit influence the load path and overall stress distribution.

Project actions

01When investigating stress in composite parts, consider both open holes and holes with fasteners.
02Use DIC to visualize strain patterns around holes and compare different configurations.

Method & Evidence

AimTo experimentally and analytically characterize stress and strain distribution in composite plates with open and filled holes, considering different stacking sequences and thicknesses.

MethodExperimental and Analytical

ProcedureComposite plates with varying stacking sequences (quasi-isotropic and cross-ply) and thicknesses (8-ply and 12-ply) were fabricated using resin infusion. Digital Image Correlation (DIC) was used to measure surface strains. Stress distributions were calculated using DIC data and laminate theory. Stress concentration factors (SCF) were estimated using Whitney and Nuismer's Point Stress Criterion (PSC) and Average Stress Criterion (ASC). Experimental stress distributions were validated against Lekhnitskii's analytical model. SCFs for cross-ply and quasi-isotropic laminates were compared with PSC and ASC predictions. Hole deformation was analyzed longitudinally and transversely using DIC and virtual extensometers.

ContextAerospace and automotive structural components, general composite material design.

Variables

IV["Hole type (open vs. filled/fastened)","Stacking sequence (quasi-isotropic vs. cross-ply)","Plate thickness (8-ply vs. 12-ply)"]

DV["Stress distribution","Strain distribution","Stress concentration factor (SCF)","Hole deformation"]

CV["Composite material (carbon taffeta 3K in epoxy matrix)","Fabrication process (resin infusion)","Loading conditions (tension)","Hole diameter"]

Strengths & Limitations

Strengths

+Combines experimental measurements with analytical modeling for validation.
+Investigates multiple influential parameters (layup, thickness, hole type).

Limitations

The complexity of composite layups and the precise fit of fasteners can be difficult to control and replicate accurately in a student design project.

Reliability & validity

The use of DIC and comparison with analytical models (Lekhnitskii, PSC, ASC) enhances the validity of the experimental findings. The study's reliability would be further strengthened by repeating tests with multiple samples for each condition.

Think critically

To what extent can fastener design alone compensate for suboptimal material selection or layup in critical composite structures?

Design Principles

"Fastener integration can serve as a passive stress management technique in composite structures."

This insight is crucial for designers and engineers working with composite materials in structural applications. Understanding how fasteners influence stress concentration allows for more optimized designs, potentially reducing material usage and weight while maintaining structural integrity.

What This Means for Your Design

Putting a bolt or rivet in a hole in a composite part makes the stress around the hole more even, no matter how the layers of the composite are arranged.

How to use in your project

1.Reference this study when discussing the impact of design features like holes and fasteners on the structural performance of composite materials in your design project.

Add to My Project

Quick Cite

Paragraph starter

Research indicates that the presence of fasteners in holes within composite laminates significantly alters stress distribution, often equalizing stress across different stacking sequences. For instance, a study by Lakis (2020) found that introducing fasteners diminished the impact of quasi-isotropic versus cross-ply layups on stress distribution, suggesting that fastener design can be a critical factor in optimizing composite structural performance.

Source

PolyPublie (École Polytechnique de Montréal)

Experimental and Analytical Stress and Strain Characterization of Notched Composite Plates

journal · 2020

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Questions About This Research

What does the research say about hole-filling fasteners significantly equalize stress distribution in composite laminates, negating stacking sequence effects?: When designing composite structures with holes, consider the use of fasteners not just for assembly but as a means to improve overall stress distribution and reduce sensitivity to layup variations. Evidence: PolyPublie (École Polytechnique de Montréal) (2020).
Why does "Hole-filling fasteners significantly equalize stress distribution in composite laminates, negating stacking sequence effects." matter for design?: This insight is crucial for designers and engineers working with composite materials in structural applications. Understanding how fasteners influence stress concentration allows for more optimized designs, potentially reducing material usage and weight while maintaining structural integrity.
How can designers apply this research?: When designing composite structures with holes, consider the use of fasteners not just for assembly but as a means to improve overall stress distribution and reduce sensitivity to layup variations.
What were the main findings?: Open-hole cross-ply composites with thinner layups exhibited better stress distribution capabilities than thicker ones.. Open-hole quasi-isotropic composites with thicker layups showed better stress distribution than thinner ones.. When holes were filled with fasteners, the stress distribution capabilities of cross-ply and quasi-isotropic laminates became nearly equal, diminishing the impact of stacking sequence.. The Point Stress Criterion (PSC) provided a very good approximation of the Stress Concentration Factor (SCF).
What research method was used?: Experimental and Analytical.
How strong is the evidence?: Evidence strength is rated Strong effect, based on a 2020 journal from PolyPublie (École Polytechnique de Montréal).
What should I do differently in my next project?: When designing bolted or riveted joints in composite panels, analyze the stress concentration around the holes and consider how the fastener's presence and fit influence the load path and overall stress distribution.
What are the limitations?: The study focused on specific composite materials (carbon taffeta 3K in epoxy matrix) and fabrication methods (resin infusion). Results may vary with different material systems, manufacturing processes, and fastener types/fits.