Understanding the Strength of Epoxy Adhesives
When evaluating the strength of epoxy, it is important to know which type of strength is most relevant to your application. Technical datasheets often include a variety of mechanical strength values. Some may list only one, while others offer several. Understanding what each value represents and how it applies to your use case is essential when selecting the right epoxy adhesive or potting compound.
Common strength measurements include shear strength, compressive strength, flexural strength, and peel strength.
Shear Strength
Shear strength is one of the most frequently cited properties of epoxy adhesives, especially in structural bonding. The most common test for this is lap shear strength, measured according to the ASTM D1002 method. This test uses a single lap joint bonded with epoxy on standardized etched aluminum.
The value is calculated by applying force until the bond fails and is expressed in pounds per square inch (psi). Since the bond area is typically 0.5 square inches, the measured force is doubled to determine the final lap shear strength.
There are two main types of bond failure:
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Adhesive failure occurs when the epoxy completely separates from one of the surfaces.
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Cohesive failure happens when the adhesive splits internally, leaving residue on both surfaces.
An epoxy with a lap shear strength greater than 2,500 psi is considered high strength. Epoxyset products such as EB-260, EB-316M, EB-127TC, and EB-135 offer excellent performance in this category.
Die Shear Strength (Semiconductor Industry)
Die shear strength is particularly important in semiconductor applications. It measures how well a die is bonded to a substrate by applying stress parallel to the bond. A high die shear strength is generally considered to be above 3,400 psi (or 10 kilograms of force). Epoxyset formulations like EO-24, EO-30M-1, and EB-470 are specifically designed for these high-performance requirements.
Compressive Strength of Epoxy
Compressive strength refers to the epoxy’s ability to withstand force without being crushed or deformed. This property is critical in applications where the material is subjected to high pressure or weight.
Standard epoxy materials usually have compressive strength values around 10,000 psi. However, specialized products such as Epoxyset’s EC-1850FT and EC-1850FT-LV achieve values exceeding 25,000 psi. To put this in perspective, high-quality concrete typically has a compressive strength of only about 5,000 psi.
Flexural Strength
Flexural strength, also known as bend strength, describes how much a material can bend under load before breaking or deforming. In this test, a bar of epoxy is supported on both ends while force is applied in the middle. This metric is vital for applications where the adhesive must resist bending stress.
Peel Strength
Peel strength measures the average force required to separate two bonded materials by peeling them apart at a 180-degree angle at a standard rate, often 6 inches per minute. Adhesives with high peel strength tend to be semi-flexible, which allows them to absorb force without cracking. This makes them ideal for assemblies that require resistance to vibration or mechanical shock.
Epoxyset manufactures toughened epoxy adhesives with excellent peel strength, including EB-260, EB-316M, EB-116, and EB-127TC. These products are widely used in electronics, medical devices, and industrial settings where long-term durability is a priority.
