Short answer

Implement stringent process controls to minimize void formation during liquid infusion molding of NCF composites when high tensile strength is a design requirement.

Field: Final Production
Source: Advanced Manufacturing Polymer & Composites Science (2015)
Method: Experimental analysis and simulation
Evidence: Strong effect

Manufacturing-induced voids in Non-Crimp Fabric (NCF) carbon/epoxy laminates significantly impair their tensile strength by hindering multiple cracking, but have a negligible impact on Mode I fracture toughness. This final production research insight is drawn from a 2015 study published in Advanced Manufacturing Polymer & Composites Science. Using Experimental analysis and simulation, researchers explored how this design variable affects real-world outcomes. The key design takeaway: Implement stringent process controls to minimize void formation during liquid infusion molding of NCF composites when high tensile strength is a design requirement.

Study

Final ProductionHigh ImpactStrong effect

Void content in NCF laminates reduces tensile strength but not fracture toughness

Advanced Manufacturing Polymer & Composites Science · 2015

Key Findings

01The presence of voids detrimentally affected the multiple cracking process in cross-ply laminates during tensile testing.
02Void content had a negligible influence on Mode I fracture toughness in DCB tests, with propagation toughness even being higher in specimens with voids.
03Local void shape and resulting stress/strain concentrations are fundamental parameters in understanding damage initiation.

Application

Design takeaway

Implement stringent process controls to minimize void formation during liquid infusion molding of NCF composites when high tensile strength is a design requirement.

How to apply

When designing with NCF composites, consider performing tensile tests on samples produced with your intended manufacturing process to assess the impact of potential void content on ultimate tensile strength.

Project actions

01When fabricating composite samples, pay close attention to resin degassing and bleeding times to control void content.
02Use microscopy to visually confirm the presence and distribution of voids in your test specimens.

Method & Evidence

AimTo investigate the influence of manufacturing-induced voids on damage initiation and propagation in carbon/epoxy NCF laminates.

MethodExperimental analysis and simulation

ProcedureTwo sets of NCF carbon/epoxy laminates were produced using liquid infusion molding: one with degassed resin and long bleeding time (low void content), and another without degassing and short bleeding time (high void content). Microscopy was used to confirm void content. Incremental static tensile tests on cross-ply specimens and Double Cantilever Beam (DCB) tests on specific laminate configurations were performed. Finite element analyses were conducted to model void geometry and stress concentrations.

ContextComposite materials manufacturing, specifically Non-Crimp Fabric (NCF) carbon/epoxy laminates.

Variables

IVVoid content (high vs. low)

DVTensile strength, Mode I fracture toughness

CVComposite material type (carbon/epoxy NCF), manufacturing method (liquid infusion molding), laminate lay-up, specimen geometry, testing conditions.

Strengths & Limitations

Strengths

+Direct comparison of two distinct processing conditions.
+Utilized both experimental testing and finite element analysis for a comprehensive understanding.
+Investigated multiple damage mechanisms (multiple cracking, fracture).

Limitations

The specific type of composite (NCF carbon/epoxy) and manufacturing method (liquid infusion molding) may limit the direct applicability to other material systems or processes.

Reliability & validity

The use of microscopy and standardized mechanical tests (tensile, DCB) enhances the reliability and validity of the findings. However, the specific material and manufacturing process might limit generalizability.

Think critically

To what extent would the findings regarding void influence on fracture toughness change if the composite material was subjected to fatigue loading instead of static loading?

Design Principles

"Process-induced defects can have differential impacts on various mechanical properties of composite materials."

Understanding how manufacturing defects like voids affect composite material performance is crucial for ensuring product reliability and safety. This insight guides material selection and process control in applications where both tensile load bearing and crack resistance are critical.

What This Means for Your Design

Making composite parts with bubbles (voids) inside makes them break more easily when you pull them, but it doesn't make them much easier to crack open.

How to use in your project

1.Reference this study when discussing how manufacturing processes, such as resin infusion, can introduce defects like voids that impact material properties like tensile strength and fracture toughness.

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Quick Cite

Paragraph starter

Research indicates that manufacturing-induced voids in NCF carbon/epoxy laminates, produced via liquid infusion molding, can significantly reduce tensile strength by impeding multiple cracking mechanisms. However, these voids exhibit a negligible influence on Mode I fracture toughness, with propagation values potentially increasing in void-containing specimens. This suggests that process control to minimize voids is critical for tensile-dominated applications, while fracture-critical designs may tolerate a higher void content.

Source

Advanced Manufacturing Polymer & Composites Science

Influence of manufacturing induced defects on damage initiation and propagation in carbon/epoxy NCF laminates

journal · 2015

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Questions About This Research

What does the research say about void content in ncf laminates reduces tensile strength but not fracture toughness?: Implement stringent process controls to minimize void formation during liquid infusion molding of NCF composites when high tensile strength is a design requirement. Evidence: Advanced Manufacturing Polymer & Composites Science (2015).
Why does "Void content in NCF laminates reduces tensile strength but not fracture toughness" matter for design?: Understanding how manufacturing defects like voids affect composite material performance is crucial for ensuring product reliability and safety. This insight guides material selection and process control in applications where both tensile load bearing and crack resistance are critical.
How can designers apply this research?: Implement stringent process controls to minimize void formation during liquid infusion molding of NCF composites when high tensile strength is a design requirement.
What were the main findings?: The presence of voids detrimentally affected the multiple cracking process in cross-ply laminates during tensile testing.. Void content had a negligible influence on Mode I fracture toughness in DCB tests, with propagation toughness even being higher in specimens with voids.. Local void shape and resulting stress/strain concentrations are fundamental parameters in understanding damage initiation.
What research method was used?: Experimental analysis and simulation.
How strong is the evidence?: Evidence strength is rated Strong effect, based on a 2015 journal from Advanced Manufacturing Polymer & Composites Science.
What should I do differently in my next project?: When designing with NCF composites, consider performing tensile tests on samples produced with your intended manufacturing process to assess the impact of potential void content on ultimate tensile strength.
What are the limitations?: The study focused on specific laminate configurations and loading modes (tensile and Mode I fracture). The influence of voids on other failure modes or under different loading conditions may vary.