Adhesives are everywhere in industrial production and daily life—from electronic product assembly to building structure reinforcement, auto manufacturing to medical device bonding. Their performance directly impacts product quality and reliability!
Among all performance indicators, Bonding Strength is the core metric for measuring adhesive mechanical properties, and the most valuable reference for buyers. In fact, it’s not a single index—it includes three key dimensions: Shear Strength, Tensile Strength, and Peel Strength. Comprehensive testing must cover these three aspects! ✅
🔹 Core Components of Adhesive Bonding Strength
Bonding strength reflects an adhesive’s ability to resist external forces and maintain Bonded Joint integrity. Each index targets different force scenarios—let’s break them down with test data and standards! 📊
1.1 Shear Strength Testing 🛠️
Shear Strength resists Shear Force (parallel to the bonding surface)—critical for structural bonding (e.g., auto chassis parts, electronic component fixing). Insufficient shear strength leads to joint slipping or fracture!
Common test method: Single-Lap Joint. But per ASTM D3528 Standard, Double-Lap Shear Test is more recommended—it balances stress distribution, reducing interference from Peel Stress and Splitting Stress (common in single-lap tests).
Test Data: For a brand of Epoxy Adhesive, average shear strength is 25MPa (single-lap) vs. 28MPa (double-lap)—proving double-lap tests better reflect real performance! 🔍
Key Tips: Clean & roughen bonding surfaces (800-grit sandpaper boosts repeatability by 25%); control test speed at 1-5mm/min (compliant with ISO 4587 Standard).
1.2 Tensile Strength Testing 📏
Tensile Strength resists Tensile Force (perpendicular to the bonding surface)—vital for load-bearing components (e.g., aerospace structures, EV battery module bonding).
Test Process: Apply adhesive evenly on standard samples, cure, then pull via Tensile Testing Machine until fracture. Calculate strength using maximum load and bonding area.
Performance Comparison: Polyurethane Adhesives (10-30MPa) vs. Acrylate Adhesives (30-50MPa)—choose based on application and force requirements!
Key Tip: Optimal adhesive layer thickness: 0.1-0.5mm (strength drops 10-15% if >1mm due to uneven stress transfer).
1.3 Peel Strength Testing 🧩
Peel Strength reflects adhesion between adhesive and Adherend Surface—critical for flexible bonding (e.g., consumer electronics film, auto interiors, packaging).
Three key influencing factors (strict control required!):
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Stress Distribution: Use ASTM D903 Standard roller clamps for uniform stress (plane clamps cause edge stress concentration, deviation >30%).
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Peel Angle: 180-degree test is standard. Strength decreases as angle increases from 90° to 180° (vertical adhesion component reduces).
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Adhesive Layer Thickness: 0.1-0.3mm recommended (too thin: insufficient filling; too thick: stress concentration & curing defects).
🔹 Comprehensive Evaluation & Selection Guidelines
Real-world bonding structures bear multiple forces—never rely on a single index! Follow the "scenario-oriented + multi-index synergy" principle:
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Shear Strength: For lateral force scenarios (auto chassis, electronic fixing);
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Tensile Strength: For vertical load-bearing scenarios (aerospace, battery modules);
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Peel Strength: For flexible/bond-separating scenarios (film bonding, packaging).
Pro Tip: Combine with Long-Term Aging Tests (85℃/85% RH for 1000h)—strength decreases by 8-12% (shear/tensile) and 15-20% (peel) after aging! ⏳
📚 References
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ASTM D3528-21: Strength Properties of Double Lap Shear Adhesive Joints
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ISO 4587: Tensile Lap-Shear Strength of Bonded Assemblies
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ASTM D903-17: Peel/Stripping Strength of Adhesive Bonds
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Study on Adhesive Tensile Strength Testing Methods & Influencing Factors. Journal of Materials Science and Engineering.
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Henkel (2023): Adhesive Strength Testing Guide for Industrial & Electronic Applications
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SAE (2022): Bonding Strength Requirements for EV Battery Components
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