Short answer

In composite-aluminum bolted assemblies, proactively incorporate shims to manage stress concentrations arising from manufacturing gaps, thereby enhancing structural reliability.

Field: Final Production
Source: International Journal of Aerospace Engineering (2020)
Method: Experimental and Simulation Analysis
Evidence: Strong effect

The choice of shim material and thickness in composite-aluminum bolted structures can dramatically alter stress and strain concentrations, influencing structural integrity. This final production research insight is drawn from a 2020 study published in International Journal of Aerospace Engineering. Using Experimental and simulation analysis, researchers explored how this design variable affects real-world outcomes. The key design takeaway: In composite-aluminum bolted assemblies, proactively incorporate shims to manage stress concentrations arising from manufacturing gaps, thereby enhancing structural reliability.

Study

Final ProductionHigh ImpactStrong effect

Shim selection significantly impacts stress distribution in composite-aluminum bolted joints

The choice of shim material and thickness in composite-aluminum bolted structures can dramatically alter stress and strain concentrations, influencing structural integrity.

International Journal of Aerospace Engineering · 2020

Key Findings

01Shims can reduce X-direction strain by 8.31%-70.97% in composite laminates.
02Liquid shims offer limited reduction (up to 23.93%) in Y-direction strain for large gaps.
03Liquid and fiberglass shims can homogenize stress distribution and improve interlaminar element stress states when shim thickness exceeds 0.8 mm.

Application

Design takeaway

In composite-aluminum bolted assemblies, proactively incorporate shims to manage stress concentrations arising from manufacturing gaps, thereby enhancing structural reliability.

How to apply

When designing bolted connections for composite-aluminum structures, specify a shim thickness and material that has been validated to reduce stress concentrations for the anticipated assembly gap.

Project actions

01Consider the manufacturing tolerances of your chosen materials when designing joints.
02Investigate how different gap-filling techniques could affect the structural performance of your design.

Method & Evidence

AimHow do different types and thicknesses of shims affect the strain and stress distribution in composite-aluminum hybrid bolted structures with assembly gaps?

MethodExperimental and Simulation Analysis

ProcedureA simplified model of a composite-aluminum assembly was created. Different shimming methods (forced assembly, liquid shim, peelable fiberglass shim) were investigated. A bolt connection experimental device was used to apply preload, and a 3D-DIC system measured surface strain. Finite element analysis was employed to study interlaminar stress and damage.

ContextAerospace structural assembly

Variables

IV["Type of shim (forced assembly, liquid shim, peelable fiberglass shim)","Shim thickness","Gap size"]

DV["Strain in X-direction","Strain in Y-direction","Interlaminar stress distribution"]

CV["Material properties (composite and aluminum)","Bolt preload","Geometry of the bolted joint"]

Strengths & Limitations

Strengths

+Combines experimental measurement with finite element simulation for a comprehensive analysis.
+Investigates multiple types of shims and their impact on stress and strain.

Limitations

The complexity of real-world assembly processes, including bolt tightening procedures and environmental factors, were not fully captured in this simplified model.

Reliability & validity

The use of a 3D-DIC system and finite element modeling enhances the validity of the strain and stress measurements. However, the reliability of the results may depend on the accuracy of the material properties used in the FEA and the precision of the experimental setup.

Think critically

To what extent does the 'ideal' shim thickness identified in this study translate to real-world applications, considering variations in bolt preload and material fatigue?

Design Principles

"Utilize gap-filling materials (shims) in hybrid bolted joints to mitigate stress concentrations and ensure uniform load distribution."

Achieving precise fits in hybrid structures is challenging due to manufacturing tolerances. Understanding how different shimming strategies affect stress distribution is crucial for preventing premature failure and ensuring the long-term performance of aerospace components.

What This Means for Your Design

When you bolt together parts made of different materials like composites and aluminum, there might be small gaps because the composite part isn't perfectly shaped. These gaps can cause stress to build up in bad places. Using shims (like thin layers) can help fill these gaps, spread the stress out better, and stop the part from breaking.

How to use in your project

1.Reference this study when discussing the challenges of assembling composite-metal structures and how your design addresses potential stress concentrations due to manufacturing inaccuracies.

Add to My Project

Quick Cite

Paragraph starter

The assembly of composite-aluminum hybrid structures often involves gaps due to the inherent manufacturing tolerances of composite materials. Research by Yue et al. (2020) highlights that these gaps can lead to complex stress and strain states, potentially compromising structural integrity. Their findings indicate that the strategic use of shims, particularly fiberglass or liquid shims exceeding 0.8 mm in thickness, can significantly reduce strain and homogenize stress distribution in bolted joints, thereby improving the overall mechanical performance and preventing localized damage.

Source

International Journal of Aerospace Engineering

Effect of Gap and Shims on the Strain and Stress State of the Composite-Aluminum Hybrid Bolted Structure

journal · 2020

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Questions About This Research

What does the research say about shim selection significantly impacts stress distribution in composite-aluminum bolted joints?: In composite-aluminum bolted assemblies, proactively incorporate shims to manage stress concentrations arising from manufacturing gaps, thereby enhancing structural reliability. Evidence: International Journal of Aerospace Engineering (2020).
Why does "Shim selection significantly impacts stress distribution in composite-aluminum bolted joints" matter for design?: Achieving precise fits in hybrid structures is challenging due to manufacturing tolerances. Understanding how different shimming strategies affect stress distribution is crucial for preventing premature failure and ensuring the long-term performance of aerospace components.
How can designers apply this research?: In composite-aluminum bolted assemblies, proactively incorporate shims to manage stress concentrations arising from manufacturing gaps, thereby enhancing structural reliability.
What were the main findings?: Shims can reduce X-direction strain by 8.31%-70.97% in composite laminates.. Liquid shims offer limited reduction (up to 23.93%) in Y-direction strain for large gaps.. Liquid and fiberglass shims can homogenize stress distribution and improve interlaminar element stress states when shim thickness exceeds 0.8 mm.
What research method was used?: Experimental and Simulation Analysis.
How strong is the evidence?: Evidence strength is rated Strong effect, based on a 2020 journal from International Journal of Aerospace Engineering.
What should I do differently in my next project?: When designing bolted connections for composite-aluminum structures, specify a shim thickness and material that has been validated to reduce stress concentrations for the anticipated assembly gap.
What are the limitations?: The study focused on a simplified model; real-world assembly complexities may introduce additional variables. The effectiveness of liquid shims was limited in cases of large gaps.