Compression testing is one of the types of mechanical testing essential for the design of safe packaging, capable of protecting goods during the distribution cycle. We analyze what is compression testing, its advantages, types of compressive testing and some regulations.
What is compression testing?
The compression test helps to determine the behavior of a material under compressive forces.
Through compression testing, it is possible to determine the force-deformation curves of a material, in addition to its limit and elastic strength, as well as its compressive strength. It is one of the essential testing methods in many industries, including electronics, automotive, construction and the medical device sector.
In the case of the packaging industry, the compression test is becoming essential in the testing of carton packaging and other packaging materials. Regarding the testing equipment to be used, it is possible to carry out the test by means of universal testing machines or a specific compression machine such as the Compression Tester that, through special load application plates , applies compression on a test sample.
The advantages of compression testing in the packaging context
Compression testing is useful at various stages of the packaging selection process: from design to production and quality control. It is a useful test to analyze the chosen materials against compression forces, characterizing them and observing their behavior.
This, in turn, translates into a number of advantages:
- Improved safety. During the distribution cycle, goods can be stacked incorrectly and be affected by compression forces, which jeopardize product safety. The compression test allows the design of safe packaging solutions, adapted to the realities of transport, storage and handling of the product, as well as testing their effectiveness.
- Economic savings. Packaging optimization through compression testing means eliminating unnecessary costs due to wastage during the distribution cycle and studying more economically efficient solutions (use of fewer materials, reduction of the weight of the unit load…).
- Sustainability. Cardboard is now considered a sustainable material, with at least 70% of corrugated cardboard boxes being recovered for recycling. However, compression testing goes one step further, eliminating unnecessary packaging and thus reducing the carbon footprint without compromising the integrity of the goods inside.
Types of compression testing
> Uniaxial compression testing
This is a compression test in which the compression forces are applied in a single axis, making it a perfect complement to the tension tests.
> Fatigue testing
Fatigue testing seeks to find the permanent change at the level of structure in a material after subjecting it to compressive forces in a progressive manner, which may end in failure.
> Force deformation curve tests
These tests are intended to define the elastic strength and plasticity of the material when subjected to compressive forces. Many materials present an elastic behavior prior to their deformation or rupture, which is defined by the existence of a linear relationship between the compressive force and the deformation. This means that the sample will start to deform when the compressive force is applied on the sides of the box, but will take its original shape and size when it is removed, as long as the point where the material exhibits plastic behavior is not reached. In this case, the box will deform or break without returning to its initial state.
>Resistance verification tests
These tests are used to test and compare the properties of materials against compressive forces. The information extracted about the strength of such materials is essential during the design or validation stage of Packaging.
Compression testing regulations
The ASTM D642 standard comprises a standard test method for determining the compressive strength of shipping containers, components and unit loads. This test method measures the compressive strength of various types of packaging and unit loads, as well as their components. The shipping containers to be tested include various formats such as boxes, pails, drums, etc.
An international standard that specifies two methods for testing full and complete packages against compressive forces. The protocol can be carried out as a single test to analyze deformation, collapse or failure of the specimen, or as part of a sequence of tests to determine the ability of the packaging to withstand the distribution cycle.
One of the most important Tappi standards for packaging. This method is used to measure the ability of corrugated or solid fiber shipping containers to resist external compressive forces.
Describes the specifications of the equipment needed to perform compressive testing on materials such as paper, cardboard and corrugated fiberboard. Two options of compression machines are included: the compression tester with fixed platforms, which applies forces at a constant rate; and those using one platform at a fixed rate and another with a deformable bar, where neither the rate nor the pressure is constant.
Compression testing is also essential to ensure cargo safety during transport. These tests can be combined with stability tests to optimize load stability and stiffness.
By studying the evolution of the force-deformation curve and performing the fatigue study of a box, it is possible to extrapolate when that box will fail if it is on the bottom of a pallet, with other boxes stacked on top of it. When a box on the bottom of the stack of boxes on the pallet fails, it can cause the rest of the load it supports to fall off, thus compromising the stability of the unit load.
Therefore, another way to use the compressometer is to reproduce the damage suffered by the load and then subject it to a stability test to see how it behaves in transport, simulating what would happen to the unit load after being stored for a considerable time.