Background Pressure-sensitive adhesives (PSAs) are widely used in structural tapes, medical devices, and flexible electronics, where joints often consist of multiple discrete adhesive pads rather than a single continuous layer. While surface patterning is known to influence stress distribution and fracture behavior, the role of macro-scale adhesive size and geometry on PSA performance under monotonic and cyclic shear loading remains insufficiently understood. Objective This study aims to determine how adhesive pad size and geometric patterning influence the static shear strength and cyclic durability of PSA joints. Methods Acrylic foam PSA (3 M 414H, 1 mm thickness) was patterned into circular, square, and strip geometries arranged in 1 × 1 to 4 × 4 arrays while maintaining a constant total bonded area (≈962 mm2). Lap-shear specimens were fabricated using acrylic adherends and tested under displacement-controlled monotonic loading (10 mm/min; nominal shear strain rate ≈0.167 s⁻1). Maximum nominal shear stress and strain at peak stress were extracted. Size-scaling experiments were conducted on circular pads to isolate characteristic length effects. Cyclic tests were performed on circular arrays under displacement-controlled oscillation (5 mm peak-to-peak, 10 Hz) using an ElectroForce system with a 1 kg suspended load. Cycles to failure were calculated from test duration. Results Under monotonic loading, single 1 × 1 pads exhibited the highest shear strength, with peak stresses ranging from approximately 0.37 ± 0.03 to 0.46 ± 0.03 MPa depending on geometry. Increasing array feature count (1 × 1 to 4 × 4) reduced peak shear stress for circular and square patterns, with 4 × 4 circular arrays decreasing to ~ 0.160 ± 0.004 MPa. Strip geometries retained comparatively higher peak stresses at intermediate array densities and exhibited orientation-dependent behavior. Size-scaling of single circular pads showed minimal dependence of peak stress on diameter (≈0.41 ± 0.04 to 0.46 ± 0.03 MPa), indicating limited intrinsic size effects. Under cyclic loading, fatigue lifetime decreased monotonically with increasing array density: 1 × 1 arrays survived approximately 7.7 × 104 cycles, compared to ~ 4.4 × 104 and ~ 3.4 × 104 cycles for 2 × 2 and 3 × 3 arrays, respectively. Conclusions PSA adhesion performance under both static and dynamic shear loading appears to be influenced by adhesive geometry rather than total bonded area alone. Partitioning a continuous adhesive layer into multiple discrete features increases edge effects, promotes stress concentration, and accelerates fatigue failure. While geometric patterning enables tunable load transfer and compliance, continuous adhesive pads provide superior load-bearing capacity and durability under shear. These findings establish adhesive geometry as a critical design parameter for PSA joints operating in monotonic and vibrational environments.

Experimental Study of the Impact of Pressure Sensitive Adhesive Size and Shape on Lap Joint Strength

期刊论文
发表日期：

2026年6月2日

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V. Dutt,
R. J. Chambers,
S. Cai

摘要

Background

Pressure-sensitive adhesives (PSAs) are widely used in structural tapes, medical devices, and flexible electronics, where joints often consist of multiple discrete adhesive pads rather than a single continuous layer. While surface patterning is known to influence stress distribution and fracture behavior, the role of macro-scale adhesive size and geometry on PSA performance under monotonic and cyclic shear loading remains insufficiently understood.

Objective

This study aims to determine how adhesive pad size and geometric patterning influence the static shear strength and cyclic durability of PSA joints.

Methods

Acrylic foam PSA (3 M 414H, 1 mm thickness) was patterned into circular, square, and strip geometries arranged in 1 × 1 to 4 × 4 arrays while maintaining a constant total bonded area (≈962 mm²). Lap-shear specimens were fabricated using acrylic adherends and tested under displacement-controlled monotonic loading (10 mm/min; nominal shear strain rate ≈0.167 s⁻¹). Maximum nominal shear stress and strain at peak stress were extracted. Size-scaling experiments were conducted on circular pads to isolate characteristic length effects. Cyclic tests were performed on circular arrays under displacement-controlled oscillation (5 mm peak-to-peak, 10 Hz) using an ElectroForce system with a 1 kg suspended load. Cycles to failure were calculated from test duration.

Results

Under monotonic loading, single 1 × 1 pads exhibited the highest shear strength, with peak stresses ranging from approximately 0.37 ± 0.03 to 0.46 ± 0.03 MPa depending on geometry. Increasing array feature count (1 × 1 to 4 × 4) reduced peak shear stress for circular and square patterns, with 4 × 4 circular arrays decreasing to ~ 0.160 ± 0.004 MPa. Strip geometries retained comparatively higher peak stresses at intermediate array densities and exhibited orientation-dependent behavior. Size-scaling of single circular pads showed minimal dependence of peak stress on diameter (≈0.41 ± 0.04 to 0.46 ± 0.03 MPa), indicating limited intrinsic size effects. Under cyclic loading, fatigue lifetime decreased monotonically with increasing array density: 1 × 1 arrays survived approximately 7.7 × 10⁴ cycles, compared to ~ 4.4 × 10⁴ and ~ 3.4 × 10⁴ cycles for 2 × 2 and 3 × 3 arrays, respectively.

Conclusions

PSA adhesion performance under both static and dynamic shear loading appears to be influenced by adhesive geometry rather than total bonded area alone. Partitioning a continuous adhesive layer into multiple discrete features increases edge effects, promotes stress concentration, and accelerates fatigue failure. While geometric patterning enables tunable load transfer and compliance, continuous adhesive pads provide superior load-bearing capacity and durability under shear. These findings establish adhesive geometry as a critical design parameter for PSA joints operating in monotonic and vibrational environments.