Reference
Technical Glossary
Mechanical Properties
- Tensile StrengthMaximum stress a bond withstands when pulled perpendicular to the bond plane. Measured in MPa or N/mm².
- Lap Shear StrengthForce required to slide two bonded substrates apart along the bond plane. Primary metric for structural adhesives.
- Peel StrengthForce needed to peel a flexible bonded element from a substrate. Reported in N/mm or N/25mm.
- Elongation at BreakMaximum stretch a cured adhesive tolerates before fracture, expressed as % of original length.
- Shore HardnessCured rigidity scale — Shore A for flexible/elastomeric, Shore D for rigid adhesives.
- Young's ModulusElastic stiffness of cured adhesive under low strain. Higher values indicate a more rigid bond.
- Impact ResistanceAbility of a bond to absorb sudden shock loads without fracturing; critical in dynamic assemblies.
Cure & Processing
- Fixture TimeMinimum time before a bonded assembly can be handled without disturbing the joint.
- Full Cure TimeTime required for adhesive to reach its ultimate mechanical properties under specified conditions.
- Open TimeMaximum working window between adhesive application and substrate mating before bond quality degrades.
- Pot LifeTime a mixed two-part adhesive remains workable before viscosity increases unacceptably.
- Mixed RatioRequired volumetric or gravimetric ratio of Part A to Part B in two-component systems.
- ThixotropyProperty of a gel adhesive to thin under shear and recover viscosity at rest — prevents sag on vertical surfaces.
- Cure MechanismChemical process driving crosslinking: anaerobic, UV, moisture, heat-activated, or room-temperature curing.
Physical Properties
- ViscosityResistance to flow, measured in mPa·s or cP. Thin formulations have low viscosity; gels are high viscosity.
- DensityMass per unit volume of the uncured adhesive, typically reported in g/cm³ or g/mL.
- Flash PointLowest temperature at which adhesive vapors can ignite. Governs storage, handling, and shipping classification.
- pH ValueMeasure of acidity or alkalinity. Relevant for metal compatibility — acidic CA adhesives can corrode sensitive substrates.
- VOC ContentVolatile organic compound concentration; determines ventilation requirements and regulatory compliance.
- Shelf LifeMaximum storage period in unopened original packaging before performance properties are compromised.
- Specific GravityRatio of adhesive density to water; used for mass-to-volume calculations in dispensing applications.
Surface & Wetting
- Surface EnergyEnergy of a substrate surface that determines how well an adhesive wets and spreads. Measured in mN/m or mJ/m².
- WettingDegree to which a liquid adhesive spreads across and contacts a substrate — essential for complete bond formation.
- Contact AngleAngle formed between an adhesive droplet and a substrate surface. Lower angles indicate better wetting.
- AF — Adhesive FailureBond failure at the interface between adhesive and substrate. Often signals poor surface prep or incompatibility.
- CF — Cohesive FailureFailure within the adhesive body itself, indicating the substrate-adhesive interface is stronger than the adhesive.
- SF — Substrate FailureFailure occurring in the substrate rather than in the adhesive — indicative of a very strong bond.
- Bond Line ThicknessGap between substrates filled by adhesive; affects joint stiffness, stress distribution, and gap-fill requirements.
Thermal & Chemical
- Softening RangeTemperature span at which a thermoplastic adhesive transitions from solid to flowable state.
- Glass Transition Temp (Tg)Temperature at which cured adhesive transitions from glassy/rigid to rubbery behavior. Defines upper service limit.
- Service TemperatureContinuous operating temperature range a cured bond can withstand without performance degradation.
- CTECoefficient of Thermal Expansion — rate of dimensional change with temperature. Mismatch with substrates induces joint stress.
- Chemical ResistanceAbility of cured adhesive to withstand prolonged exposure to solvents, acids, bases, or fuels.
- Humidity ResistancePerformance retention when exposed to elevated relative humidity or direct water immersion over time.
- Acidic / AlkalinepH-based classification of adhesive chemistry — acidic CA types can corrode copper; alkaline types may attack aluminum.
Substrates & Compatibility
- LSE PlasticsLow Surface Energy plastics (PE, PP, PTFE) are inherently difficult to bond without surface treatment or specialist adhesives.
- Substrate PreparationPre-bonding treatments — abrasion, solvent wipe, plasma, or primer — applied to maximize adhesion reliability.
- PrimerChemical pre-treatment activating difficult surfaces; essential for anaerobic adhesives on passive metals.
- OutgassingRelease of trapped gases from substrate or adhesive during cure or service; can compromise bonds in sealed assemblies.
- Plasticizer MigrationTransfer of plasticizers from flexible PVC or rubber substrates into adhesive — may reduce long-term bond strength.
- Metal Oxide LayerNative oxide film on metal surfaces affecting adhesion; may require abrasion or chemical etching prior to bonding.
- Gap FillingAbility of an adhesive to bridge irregular or uneven surfaces and still form a structurally sound bond.