If you work in the packaging industry or have an idea of the packaging industry then you will know how important lab testing instruments are. The industry uses many instruments for delivering a complete product and one of the important instruments they use is a peel strength tester.
In this article, we will discuss in detail the uses of a peel strength tester and how is it different from tensile testing, and why are the different types of peel tests used to determine.
Peel tests designed for flexible adhesives are designed to measure resistance to localized stress. Therefore, the peel force is considered to be applied to a straight front. The more flexible the parts to be joined and the higher the adhesion coefficient, the more linearly the load area decreases. Then the tension becomes infinite. Applied stress and breaking stress are given as linear values, since the area under stress depends on the thickness and modulus of the parts and adhesive to be bonded, which is very difficult to determine precisely. The T peel test (ASTM D1876) is probably the most widely used peel test for thin metal bonded parts. In this test, the entire applied load is transferred to the bond. This type of isolation, therefore, tends to give the lowest value of all isolation tests
Peel test VS tensile testing
Peel testing has a significant advantage over tensile testing as it requires a much thinner electroplated coating. From a practical point of view, the coating must be strong enough to allow continuous detachment of the deposit from the substrate. However, problems can arise if the coating is brittle if continuous de-lamination is not allowed.
What do peel test results provide us?
The test results of the peel strength that we derive after conducting the test are usually expressed as a function of the peel strength. Based on practical considerations for adhesive bonds, peel tests are usually performed at 90-degree or 180-degree peel angles, or in a T-peel configuration. Peel adhesion is measured as the force across the width of the substrate when pulled at a constant speed. The peel force is constant at the beginning of the test, but once the fracture starts, it tends to fluctuate to an average value as the test progresses.
A failure can be caused by separation in one of the interfaces, or separation within one of the three constituent layers if the layer is torn instead of separating itself. The amount of peel force is a true expression of peel or cohesive failure work. There are two advantages of using the peel test over other similar test methods. First, the fracture propagates at a controlled rate, and, second, the peel force is a function of the peel work or the cohesive failure work.
Peel testing, as the name suggests, is used to assess the quality of joints as the primary stresses are peel or tensile stresses. It is therefore very useful for assessing the impact of processes (such as surface treatments) and manipulations (environmental impact) on the strength of the mating surfaces. A peel test requires at least one flexible adhesive surface. The term “flexibility” refers to the ability of the parts to be joined to bend 90° without breaking or tearing. The reported result for the peel test is the constant load per unit width required to continue peeling the joint after initiation, determined from the flat portion of the load-strain curve. Due to environmental susceptibility, the maximum load corresponding to failure occurrence is sometimes used.
The main difference between these methods is the peel angle and whether the peel angle is constant throughout the test.
Peel tests provide useful comparative data, but are unlikely to provide a quantitative measure of interfacial strength. There is no guarantee that the fracture path will follow the interface. The stress distribution inherently depends on local geometric features such as crack sharpness and de-lamination angle. The conversion of peel load to stress per unit area requires assumptions about the extent of the peel zone that is likely to be inaccurate. The T-peel test has been adopted by most standardization bodies (ISO 11339, ASTM D 1876, etc.) and is widely used to evaluate the surface preparation and environmental durability of adhesive systems. Small T-peel probes with short adhesive lengths take up less space in HVAC systems and are often used in screening programs to assess environmental performance.