PET Strapping Tensile Testing: Standards, Methods, and Applications

PET strapping tensile testing is the core quality control procedure used to evaluate the breaking strength, tensile strength, and elongation performance of polyester strapping widely used in heavy-duty packaging and load securing. This technical guide covers test specimens, applicable standards such as ASTM D3953 and ISO 13891, equipment configuration, calculation methods, and typical applications. Understanding these procedures enables manufacturers, testing laboratories, and logistics providers to verify product quality and ensure cargo safety.

Technical Overview

PET strapping, also known as plastic steel strapping or polyester strapping band, is a high-strength packaging material extruded from polyethylene terephthalate. It has become a widely adopted alternative to steel strapping due to its excellent tensile strength, high elasticity, resistance to rust and corrosion, and improved handling safety. Because PET strapping is routinely used to secure heavy loads such as steel coils, bricks, cotton bales, and paper reels, its mechanical performance must be verified through systematic tensile testing.

PET strapping tensile testing is performed on a universal testing machine to determine key parameters including breaking force, tensile strength, and elongation at break. The test results are used for product grading, incoming material inspection, packaging design, and compliance verification against standards such as ASTM D3953, ISO 13891, and GB/T 22344. Consistent and accurate tensile testing ensures that the strapping maintains sufficient strength throughout storage, transport, and handling.

Testing Samples

Standard PET Strapping Specimens

Specimens are cut directly from production rolls or delivered products. Common commercial sizes include widths of 13 mm, 16 mm, 19 mm, and 25.4 mm, with thicknesses typically ranging from 0.5 mm to 1.5 mm. Each specimen should be straight, free of visible defects such as nicks, cracks, or embedded impurities, and cut to a sufficient length to allow proper clamping, usually 600 mm to 1000 mm depending on the grip design.

Jointed Specimens

For welded or buckled strapping systems, jointed specimens are prepared to evaluate the strength of the connection point. Typical joint types include friction weld joints produced by battery-powered strapping tools, heat seal joints, and wire buckle or seal lock joints. Joint testing determines whether the connection or the parent strap fails first, which is critical for real-world load security.

Conditioned Specimens

Prior to testing, specimens should be conditioned in a standard laboratory atmosphere of 23 ± 2 °C and 50 ± 5 % relative humidity in accordance with ISO 291 for at least 24 hours. Conditioning stabilizes the polymer structure and ensures that test results are comparable between laboratories and production batches.

Testing Items

The tensile test evaluates the following mechanical properties of PET strapping:

• Breaking force (maximum tensile load before rupture), expressed in kN or N
• Tensile strength, calculated as breaking force divided by the original cross-sectional area, expressed in MPa
• Elongation at break, expressed as a percentage of the initial gauge length
• Elongation at maximum force, reflecting the deformation behavior at peak load
• Joint breaking force and joint efficiency, calculated as the ratio of joint strength to parent strap strength
• Stress-strain curve characteristics, including the elastic region and strain-hardening behavior

Testing Methods

Applicable Standards

The most commonly referenced standards include ASTM D3953 for nonmetallic strapping and joining methods, ISO 13891 for flat strapping, and GB/T 22344 for packaging strapping products. General principles may also refer to ISO 527 for the tensile testing of plastics. The specific specimen dimensions, gauge length, and test speed should always follow the requirements of the standard or specification nominated by the customer or product certification scheme.

Equipment and Setup

The test is conducted using a universal testing machine equipped with a calibrated load cell suitable for the expected breaking force. Because PET strapping is flexible and prone to slippage or premature failure at the clamp line, wrap-around bollard grips or capstan-type grips are strongly recommended; serrated wedge grips may be used with protective liners when appropriate. Elongation can be measured using a long-travel extensometer or, when permitted, crosshead displacement. The machine should offer closed-loop speed control and data acquisition software capable of recording force-extension curves.

Test Procedure

A typical tensile test on PET strapping follows these steps:

• Condition the specimens in the standard atmosphere and verify they are free of defects
• Measure the width and thickness of each specimen at three positions along the gauge region and calculate the average cross-sectional area
• Set the gauge length, commonly between 200 mm and 400 mm, according to the applicable standard
• Mount the specimen in the grips, wrap it evenly around bollards if applicable, and apply a small preload of approximately 10 N to 50 N to remove slack
• Select the test speed, typically 100 mm/min to 500 mm/min, with 100 mm/min being the most widely used value for strapping standards
• Start the test and pull the specimen to complete rupture, recording the maximum force and the extension at break
• Reject any specimen that fails at the grip contact zone and repeat until a valid result is obtained
• Test at least five valid specimens and report the arithmetic mean and standard deviation for each parameter

Result Calculation

Tensile strength is calculated by dividing the breaking force by the original cross-sectional area, where the area equals the measured average width multiplied by the average thickness. Elongation at break is calculated by dividing the extension at rupture by the initial gauge length and multiplying by one hundred. Joint efficiency is calculated by dividing the breaking force of the jointed specimen by the breaking force of the parent strapping and multiplying by one hundred; a value approaching or exceeding ninety percent is generally regarded as a reliable joint.

Applications

PET strapping tensile testing serves a wide range of industries and quality control scenarios:

• Strapping manufacturers performing batch inspection, product grading, and certification testing
• Steel, aluminum, and metal processing plants securing coils, rods, and profiles
• Building material producers palletizing bricks, blocks, tiles, and refractory products
• Textile and agricultural operations compressing cotton, fiber, and foam bales
• Paper, printing, and packaging mills handling reels and heavy carton units
• Glass, ceramics, and machinery manufacturers requiring high-strength, non-marring load securing
• Third-party laboratories conducting acceptance testing and type approval for export shipments

FAQ

What machine capacity is required for PET strapping tensile testing?

The machine capacity should be selected so that the expected breaking force falls within twenty to eighty percent of the load cell range. For light-duty 13 mm strapping, a 10 kN machine is usually sufficient, while heavy-duty 19 mm to 25.4 mm strapping may require a 20 kN to 50 kN machine. Interchangeable load cells improve measurement accuracy across different strap grades.

Which grips are best suited for flexible strapping?

Wrap-around bollard or capstan grips are the preferred solution because they distribute the clamping load along the wrapped length and prevent slippage and grip-line fracture. If wedge grips must be used, protective liners or cushioning materials should be inserted between the jaw surface and the specimen.

What test speed should be used?

A crosshead speed of 100 mm/min is the most common setting cited in strapping test standards, although speeds up to 500 mm/min are permitted in some specifications. Because PET is a strain-rate-sensitive polymer, the speed must be kept constant and identical for all comparative tests.

How many specimens should be tested?

A minimum of five valid specimens is recommended for each sample batch. Results from specimens that slip in the grips or break at the clamp line should be discarded and replaced so that the reported average reflects the true material strength.

What breaking strength is typical for PET strapping?

Breaking force varies with cross-section and grade. Common commercial 16 mm PET strapping typically achieves a breaking force of approximately 5 kN to 8 kN, while heavy-duty grades and wider straps can exceed 10 kN. The measured value should always be compared against the declared grade value and the applicable standard requirement.