Edge Crush Test: Definition, How It Works, Advantages, and Challenges

The edge crush test (ECT) is a codified international test methodology. It is used in the packaging industry to assess the strength and durability of corrugated or paperboard materials and others. 

The ECT determines the maximum compressive loading a corrugated material can withstand on its edge, before the onset of collapse. This quantifies the material's resistance to being crushed when pressure is applied along its edge. This can only be loosely interpolated in the strength of finished structures, but it provides a consistent measure across various materials that informs in this regard. 

This article will discuss what the edge crush test is and how it works. The advantages and challenges will also be covered.

What Is the Edge Crush Test (ECT)?

The ECT is a generally accepted testing method employed in the packaging industry to evaluate the strength and resilience of corrugated or paperboard materials. ECT determines a material's capacity to withstand edge loading forces, simulating the stresses experienced during stacking and transportation.

Why Is the Edge Crush Test Important?

The edge crush test ensures that samples of packaging materials meet specific strength standards, guaranteeing the reliability and integrity of resultant packaging. It helps in selecting appropriate materials. It also ensures they can withstand typical and extreme stacking and handling stresses, and safeguarding the enclosed products from damage. ECT results aid in designing efficient and cost-minimized packaging solutions by avoiding over-engineering by assuming minimal material strength. Using materials with the appropriate ECT values reduces excessive material/resource usage, reducing environmental impact in materials sourcing and disposal. Efficient packaging design also minimizes shipping volumes, reducing transport impact. The ECT promotes consistency in packaging quality and performance, by providing cross-application knowledge and consistency in materials performance understanding.

How Does ECT Work?

The ECT is a rigorous and highly repeatable test that informs deeply about a single aspect of material strength, with profound influence on real-world packaging performance. 

A small, rectangular specimen of the material is cut and conditioned to a specified humidity and temperature to ensure consistent test conditions. The conditioned specimen is placed vertically between two rigid platens on a testing machine. The specimen's edges are aligned with the platens, ensuring a secure fit. A steadily increasing compressive force is applied to the specimen's edge at a constant rate using the testing machine. The force is applied until the material buckles or collapses, identified by any sudden motion in response to increased loading. The maximum force applied before the material's edge failure is recorded as the edge crush test result.

How Much Force Does the Edge Crush Testing Require?

The force required during an ECT depends on various factors such as: the specific material being tested, its thickness, and the testing conditions. ECT is typically conducted following standardized preparation defined by organizations like the International Safe Transit Association (ISTA) and the American Society for Testing and Materials (ASTM).

A steadily increasing compressive force is applied to the clamped specimen's edge until it buckles or collapses. The force at which this failure occurs is recorded as the ECT value in lbf/in or kN/m. The measured force required varies widely with material type and thickness, but it is typically within the range of 10–60 lbf/in or 0.6–3.4 kN/m. It can exceed this range, depending on the material's type, thickness, and composition.

What Are the Advantages of the Edge Crush Test?

The ECT offers various enabling advantages in the packaging industry such as:

1. Provides an accurate measure of a material's resistance to edge compression, assisting designers and manufacturers in selecting appropriate packaging materials for specific products.
2. Ensures consistency in material assessment and facilitates reliable comparisons between divergent materials.
3. Helps in the design and execution of sufficient but minimal packaging that can withstand real-world stacking and transportation stresses. This reduces material overuse while ensuring the safety and integrity of enclosed products during transit.
4. Assists in cost-minimized packaging design, avoiding over-engineering resulting from otherwise common underestimation of the material capability.
5. Optimized material selection based on ECT results in reduced resource usage and footprint of packaging solutions.
6. Serves as a batch/sample evaluation quality-control tool, ensuring that packaging materials meet or exceed specified strength standards, reducing the risk of package strength variations over time.

How Is the Edge Crush Test Performed?

The ECT is performed following standardized procedures:

1. Cut a rectangular specimen of the to-be-tested material to the required dimensions. The sample should be conditioned to standardized temperature and humidity conditions to ensure consistent testing, compensating for the variability of card materials with changes in humidity and temperature.
2. Place the conditioned specimen vertically between the rigid platens of the ECT machine, with edges aligned precisely with the platens to ensure a secure fit.
3. Initiate the test by applying progressively increasing compressive force to the specimen's edge at a constant ramp rate, as specified by the testing standard. This rate applies until the material's edge buckles or collapses.
4. Record the maximum force applied to the specimen's edge before failure occurs. This recorded force (in lbf/in or kN/m), is the edge crush test value.
5. Use the recorded ECT value to assess the material's strength and suitability for various packaging applications, helping determine its resistance to edge compression. Experience is required in the interpretation of the ECT result as a driver of design considerations and material choices.

What Do Edge Crush Test Values Indicate?

ECT values indicate the strength and resistance of corrugated cardboard or paperboard materials to edge compression. ECT values quantify how much compressive force a material can withstand along its edge before it collapses or buckles. They help assess the ability of packaging materials—and therefore package designs—to support the weight of stacked packages. Where stacking strength is crucial, higher values are achieved by alternate material selection and by increased thickness or other material-specification alterations. ECT values assist in defining the structural integrity of packaging during transportation and storage, resulting in packaging that maintains its shape and protects the enclosed products.

How Does ECT Compare to Other Strength Tests?

ECT is one of several standardized tests used in the packaging industry to assess the strength (and other performance aspects) of packaging materials. Each test method has its focus and measures different aspects of material strength. 

The ECT measures a material's resistance to edge compression, simulating the stresses encountered during stacking. Burst strength (Mullen test), for example, assesses a material's resistance to puncture or bursting. It measures the force required to puncture a material with a blunt object. A compression test evaluates a finished package's ability to withstand vertical loads and uniform compression during storage or transportation. Tensile tests, on the other hand, assess the material's ability to withstand linear tensile forces. They are used to evaluate the tensile strength and elongation properties of materials. 

An ECT is more relevant for packaging materials in applications in which stacking strength is crucial, while burst strength is more relevant when puncture resistance is a primary concern. Both compression and edge crush tests provide different insights into packaging performance, with compression tests assessing the overall package's load-bearing capacity. As a rule, a good understanding of the interpretation of ECT results will inform the design process and materials selection and lead to a successful execution that can be evaluated by compression testing.

While tensile tests provide valuable information about material properties, an ECT is more relevant for understanding how corrugated materials perform under stacking and handling conditions. As a rule, packaging structures are used in compressive loading scenarios, so tensile resilience is a minor factor in most applications.

What Are the Edge Crush Test Standards and Regulations?

ECT corrugated testing is standardized by several organizations and testing bodies. These organizations ensure consistency and reliability in the evaluation of the strength of corrugated cardboard, paperboard, and other packaging materials. Some standards and regulations are:

1. TAPPI T 811: Provides procedures for conducting the ECT on corrugated fiberboard.
2. ISO 3037: Specifies a method for determining the edgewise compressive strength of corrugated fiberboard.
3. ISTA 3A: Evaluates the strength and performance of packaging materials and systems.
4. FEFCO Standard 8: Determines the ECT of corrugated cardboard.

While the tests do not provide directly interchangeable/comparable results, the interpretation between them is well understood and most manufacturers of materials will be able to specify their materials’ performance expectations under various test scenarios/standards.

What Device Does an Edge Crush Test Use?

ECT corrugated testing is typically conducted using a specialized testing machine known as an edge crush tester or ECT tester. These devices consist of:

1. Sample Holder: Holds the corrugated cardboard or paperboard specimen securely in a vertical position during the test.
2. Platens: Two rigid, flat platens are used to apply the compressive force to the specimen's edge. One platen is stationary, while the other is moved by a hydraulic or screw system.
3. Load Cell: This is used to measure the force applied to the specimen and record the maximum force at the point of failure/collapse.
4. Control Panel: The control panel allows operators to set testing parameters, such as loading rate and test duration, and monitor the test progress/outcome.

How Is the ECT Performed on Different Materials?

An ECT can be performed on various materials, but it is most commonly used for corrugated cardboard and paperboard materials in the packaging industry. The testing procedure remains consistent regardless of the material being tested, the primary focus being evaluating the material's resistance to edge compression.

The ECT is extensively used for corrugated cardboard, of which it assesses the strength and stacking performance of different weights/constructions—single-wall, double-wall, and triple-wall corrugated. Note that “single wall” is two skins and one corrugation layer. It is also applied to paperboard materials, including solid bleached sulfate (SBS), solid unbleached sulfate (SUS), and folding carton board, to determine the same key property.

In some cases, the ECT may be adapted for testing non-paper-based materials like plastic corrugated sheets or fiber-reinforced composites. However, the applicability and relevance of ECT to these materials may vary, and alternative testing methods can be more appropriate.

A typical single-wall corrugated card will range from 32 ECT to 44 ECT, defining the normal range for performance, the upper value being 44 lbf/in material performance. A box constructed from a typical double-wall corrugated board might achieve a 48 lbf/in material ECT value, often resulting in ECT box values of 44 ECT to 50 ECT in some cases.

What ISO Standard Applies to the ECT?

The International Organization for Standardization (ISO) provides a standard for the edge crush test (ECT) by non-waxed edge testing. Specifically, ISO 3037 is the ISO standard that defines the method for determining the edgewise compressive strength of corrugated fiberboard.

What Are the Challenges and Limitations of Edge Crush Testing?

Challenges and limitations of the ECT include:

1. Variations in material composition, structure, and manufacturing processes can greatly impact ECT results. Small differences in material properties result in significant variations in test outcomes.
2. The ECT typically tests small specimens of material, which may be poorly representative of the entire packaging structure. 
3. Many materials exhibit anisotropic behavior, meaning their strength properties can vary in different directions. An ECT primarily assesses the material's resistance to edge compression, which may not capture anisotropic characteristics, as a standard end-on corrugation orientation is not equivalent to an edge-on presentation. This influence is greatly reduced in multi-layer materials.
4. The moisture content of corrugated materials can greatly influence ECT results. 
5. Surface conditions, such as coatings or treatments, can impact ECT results. Testing should consider the surface properties of the material, ideally testing coated and uncoated samples for clarity.
6. The ECT measures material strength in a controlled laboratory setting, which will not necessarily replicate the complex conditions experienced during shipping and handling.
7. The ECT is primarily intended for corrugated cardboard and paperboard materials. It may not be ideally suited to assessing the strength of other materials used in packaging.

What Are Real World Applications of the Edge Crush Test?

The ECT is widely applied as a reference point in the packaging industry to evaluate the stacking strength and edge compression resistance of widely employed materials. Some real-world applications are:

1. ECT helps packaging professionals choose the most appropriate materials for packaging applications, ensuring that packaging can withstand the stacking pressures and handling stresses to be encountered.
2. Test results inform the design and structural integrity of packaging solutions. Designers use ECT data to develop packaging that protects products efficiently and minimizes the risk of damage.
3. Manufacturers and suppliers use the ECT to maintain assurance of consistent material quality, confirming the meeting or exceeding of specified strength standards, reducing the risk of subsequent and potentially expensive packaging failures.
4. The ECT assists in optimizing packaging materials, minimizing the over-application of resources, and contributing to a reduced footprint for packaging solutions.
5. The ECT is particularly important in industries like consumer electronics, in which fragile and extremely high-value items must be protected during shipping and handling.
6. In the food and beverage supply chain, the ECT helps reduce the storage and transportation risks of organic contaminants from damaged products.

Is the ECT Only Used for Corrugated Cardboard Materials?

ECT is primarily designed for assessing the strength and stacking performance of corrugated cardboard and paperboard materials. However, the ECT is not limited exclusively to corrugated paper/card materials. It can potentially be adapted or used as a reference test method for other materials in specific applications for which edge compression resistance is a relevant factor. This adaptation may require alterations to testing procedures or equipment to suit the characteristics of the material being tested.

While the ECT is highly applicable to corrugated materials, other materials may have their standardized testing methods or criteria for assessing their strength and performance in different contexts.

What Is the Difference Between an ECT and an Impact Test?

The two test regimes are complementary but quite different in approach. Their mode of stress application differs by 90°; so edge crush testing evaluates the performance of the sheet edge in load bearing, whereas an impact test evaluates the ability of the material’s face to withstand impact.

Both tests have high applicability in packaging design, and it is common for packaging designers to reference these and other factors in selecting material type, thickness, and orientation in real-world solutions.

Summary

This article presented the edge crush test, explained it, and discussed how it works and its various advantages. To learn more about the edge crush test, contact a Xometry representative.

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