In modern manufacturing, adhesives are increasingly at the center of production. They replace many mechanical methods such as nails, bolts, or welding. Their advantages lie in forming lightweight, neat bonds while distributing stress evenly. Adhesives are also a cost-saving solution that enhances design efficiency. To evaluate adhesive performance, engineers rely on standardized indicators. Among these, shear strength and peel strength are always mentioned first. These two parameters reflect the ability to maintain bonding under different stresses. Thanks to them, manufacturers can choose the right adhesives and extend product lifespan.
DEFINITIONS AND IMPORTANCE OF THE INDICATORS
Shear Strength
Shear strength indicates the ability of an adhesive layer to resist forces parallel to the bonded surface. This value is measured in MPa in standardized tests. It shows the resistance against sliding between two bonded substrates. A bond with high shear strength remains stable for a long time and reduces the risk of cracking. In practice, shear strength is critical across many industries. Automobiles, aircraft, and construction projects all require high levels of this property. When the adhesive is strong enough, the bond can withstand large loads, resist vibration, and extend its service life. This makes shear strength the foundation of safe and efficient operation.
Peel Strength
Peel strength reflects the force needed to separate two substrates at the edge of the bond. This value is usually measured in N/25mm in standardized tests. It shows the resistance against peeling at edges, the weakest point of any adhesive joint. This indicator is especially important for thin, light, or flexible products. Packaging, films, plywood, or electronic components all require high peel strength. If the value is low, the bond will peel easily during use. Conversely, high peel strength ensures product integrity and elevates its quality.
REFERENCE VALUES BY ADHESIVE TYPES
Each adhesive type has its own shear strength and peel strength characteristics. Two-component epoxy adhesives achieve 18–35 MPa in shear strength and 150–200 N/25mm in peel strength. They are strong, solvent-resistant, and ideal for load-bearing structures. Polyurethane offers 10–25 MPa shear strength and 80–150 N/25mm peel strength, known for toughness and vibration resistance. Acrylic adhesives show 5–15 MPa shear strength and 40–80 N/25mm peel strength. They are easy to apply, UV-resistant, and suitable for outdoor use. Silicone adhesives reach 1–5 MPa in shear strength and 20–60 N/25mm in peel strength, offering flexibility and heat resistance, often used in electronics and glass bonding.
FACTORS AFFECTING ADHESIVE STRENGTH
Substrate Material
The surface properties of the substrate directly determine adhesion. Smooth, low-energy surfaces usually make it difficult to achieve strong bonding. In contrast, surfaces that are roughened, degreased, or treated improve adhesion significantly. Increased contact area enhances load-bearing ability. Surface preparation is always considered a critical step in adhesive application.
Application Conditions
Temperature, humidity, and pressure during bonding greatly affect performance. Low temperatures slow curing, resulting in lower bond strength. High humidity can create bubbles or disrupt the polymer structure. Insufficient pressure leads to gaps and poor load transfer. Under optimal conditions, adhesives form uniform, durable layers. This is why manufacturers maintain strict process controls to ensure stable results in mass production.
Service Life and Aging
Adhesives are continuously affected by environmental factors. UV light, high temperature, humidity, and chemicals can degrade polymers, weakening bonds over time. Both shear strength and peel strength decline significantly, reducing product safety. Temperature fluctuations create internal stress, causing cracks at the interface. To avoid this, adhesives must be selected with aging and UV resistance, especially for outdoor, marine, or electronic applications.
Mixing Ratio
For two-component adhesives, the correct mixing ratio is crucial. Incorrect proportions can make the adhesive brittle and fragile or too soft to bear loads. As a result, both shear strength and peel strength decrease rapidly. Pot life also plays an important role: once exceeded, the reaction efficiency drops and the bond becomes weaker. Strict adherence to manufacturer instructions on mixing ratio and pot life ensures stable and durable performance.
REAL-WORLD APPLICATIONS
Applications of High Shear Strength
In automotive and aerospace industries, shear strength determines structural safety. Car bodies, aircraft wings, and mechanical parts require adhesive bonds that can withstand heavy loads and constant vibration. In construction, high shear strength ensures stability for laminated glass, wall claddings, and heavy decorative materials. These applications demand adhesives that not only provide strong bonds but also maintain performance in harsh environments.
Applications of High Peel Strength
In flexible packaging, peel strength ensures products do not split at the seams during storage and transport. The electronics sector requires stable peel strength to protect sensitive components and prevent delamination. In plywood and thermoplastics, high peel strength maintains edge bonding where stress is concentrated. These cases highlight the critical role of peel strength in preserving the value and reliability of the final product.
VICHEM – AUTHORIZED DISTRIBUTOR OF CERTIFIED CHEMICAL ADDITIVES IN VIETNAM
Vichem is an authorized distributor of chemical additives with full legal compliance in Vietnam. We not only provide high-quality products but also deliver after-sales services that meet international standards. Our services include:
- Technical consultation: Supporting customers in selecting suitable products for their intended applications.
- Color testing: Vichem’s experts perform color-matching tests to ensure results meet design standards.
- Application support: Assisting customers in integrating products into production lines to guarantee optimal efficiency.
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