Tensile Strength Testing of Reinforced Films: Methods, Standards, and Applications

Tensile strength testing of reinforced films is a fundamental laboratory procedure used to evaluate the mechanical performance of plastic films laminated with scrim, mesh, or woven fabric reinforcements. This article provides a comprehensive technical overview of reinforced film tensile strength determination, covering applicable international standards such as ISO 527-3, ASTM D882, ASTM D751, ISO 1421, and GB/T 1040.3, along with specimen preparation, test procedures, and typical industrial applications.

Technical Overview

Reinforced films are multi-layer composite materials in which a plastic film, typically polyethylene (PE) or polypropylene (PP), is laminated onto or between layers of woven fabric, knitted scrim, or cross-laid mesh yarns. This construction combines the flexibility, water resistance, and chemical stability of the polymer film with the high load-bearing capacity of the textile reinforcement, producing materials that are widely used in construction sheeting, tarpaulins, packaging, agriculture, and geosynthetics.

Tensile strength determination is the most widely performed mechanical test for reinforced films because it directly reflects the ability of the material to withstand pulling forces during installation, service, and transportation. Unlike homogeneous films, reinforced films exhibit strongly anisotropic behavior: the tensile properties measured in the machine direction (MD) can differ substantially from those in the transverse direction (TD), depending on the density and orientation of the reinforcing yarns. A complete characterization therefore requires testing in both principal directions.

Tensile strength determination for reinforced films is typically carried out in accredited third-party laboratories or in-house quality control laboratories using universal testing machines (UTM) equipped with appropriate grips, load cells, and extensometers. The governing test methods are drawn from ISO, ASTM, EN, and GB standards frameworks, and the selection of the correct method depends on the structure of the laminate and the intended end use of the product.

Testing Samples

Reinforced Polyethylene and Polypropylene Films

These are the most common sample types and consist of blown or cast PE/PP films laminated to a woven PP tape fabric or a cross-laid scrim. Examples include laminated tarpaulin materials, construction sheeting, scaffold coverings, and heavy-duty covers. Specimens are usually cut with the reinforcing yarns parallel to the load axis so that the yarns, rather than the film, carry the principal load.

Coated and Laminated Composite Films

This category includes textile fabrics coated on one or both sides with PVC, PE, PU, or PVDF films, such as tent fabrics, awning materials, banner substrates, and architectural membranes. Because the textile substrate dominates the tensile response, these products are generally tested using coated-fabric methods such as ASTM D751 or ISO 1421 rather than thin-film methods.

Geosynthetic Reinforced Membranes

Geomembranes and reinforced geosynthetic barriers, including reinforced GCL covers and scrim-reinforced flexible membrane liners, are tested using wide-width tensile methods such as ISO 10319 or ASTM D4595, and dumbbell or strip methods such as ASTM D6693 for smooth polyethylene liners. The wide specimen geometry better reproduces the multi-yarn load distribution that occurs in field installations.

Functional and Specialty Films

Greenhouse films reinforced with anti-tear mesh, reinforced vapor barriers, FIBC container liners, silage covers, and medical or protective laminates may also be characterized. For these products, tensile testing is frequently combined with tear resistance, puncture, and seam strength testing to provide a complete mechanical profile.

Testing Items

A comprehensive tensile strength determination program for reinforced films typically includes the following measurable parameters:

• Tensile strength (maximum tensile stress at break, expressed in MPa or N/mm of width)
• Maximum tensile force and breaking force (N), reported per unit width for fabric-reinforced structures
• Elongation at break and elongation at maximum force (%)
• Yield strength and yield strain, where a defined yield point exists
• Tensile modulus (secant or tangent modulus, MPa), derived from the initial linear region of the stress-strain curve
• Grab strength and grab elongation for coated fabrics tested by the grab procedure
• Seam or weld strength, for materials joined by heat welding, ultrasonic welding, or stitching
• Directional comparison of machine direction (MD) versus transverse direction (TD) properties

For reinforced films, results are commonly reported as force per unit width (kN/m) rather than stress, because the cross-section of the reinforcement is not always well defined and the load is carried by discrete yarns.

Testing Methods

Applicable Standards

The principal test methods referenced for reinforced film tensile strength determination include:

• ISO 527-1 and ISO 527-3: determination of tensile properties of plastics, including films up to 1 mm thickness
• ASTM D882: standard test method for tensile properties of thin plastic sheeting
• ASTM D751: standard test methods for coated fabrics, covering both strip and grab tensile procedures
• ISO 1421: rubber- or plastics-coated fabrics, determination of tensile strength and elongation at break
• ASTM D5035: breaking force and elongation of textile fabrics by the strip or grab procedure
• ISO 10319 and ASTM D4595: wide-width tensile testing of geosynthetics
• ASTM D6693: tensile properties of nonreinforced and reinforced geomembranes by strip specimens
• GB/T 1040.3 and GB/T 13022: Chinese national standards for tensile determination of plastic films, technically aligned with ISO 527-3

Specimen Preparation and Conditioning

Specimens are die-cut or precision-cut from representative sample sheets, avoiding creases, wrinkles, and areas near selvages. For strip tests, standard widths are 25 mm or 50 mm with adequate length to allow the specified gauge length plus grip engagement. At least five valid specimens per direction are recommended, and specimens are discarded if failure occurs within the grips. Prior to testing, specimens are conditioned in a standard atmosphere of 23 °C ± 2 °C and 50 % ± 5 % relative humidity for a minimum of 24 hours, in accordance with ISO 291 or ASTM D618, unless the governing product standard specifies otherwise.

Strip Tensile Test Procedure

In the strip method, a full-width specimen is gripped across its entire width and pulled to failure at a constant crosshead speed. Typical configurations include a gauge length of 100 mm with test speeds of 100 to 500 mm/min for film-type specimens, while coated-fabric strip tests per ASTM D751 commonly use a 75 mm jaw separation and a speed of 300 mm/min. The maximum force, elongation at break, and work-to-break are captured by the testing machine software, and results are calculated as force per unit width or as engineering stress when the total thickness is used.

Grab Tensile Test Procedure

The grab method uses a specimen wider than the grips, so that only the central portion of the specimen, typically 25 mm across, is loaded. This configuration concentrates the load on the reinforcing yarns crossing the grip line and is considered more indicative of localized stress conditions in service, including behavior around fasteners and eyelets. Grab testing per ASTM D751 or ASTM D5035 is the preferred procedure for many tarpaulin and coated-fabric specifications.

Wide-Width Tensile Test Procedure

For geosynthetic and structural applications, wide-width testing per ISO 10319 or ASTM D4595 employs specimens 200 mm or wider with gauge lengths of 100 mm and low strain rates, typically 10 to 20 mm/min. This method minimizes edge effects and provides load-strain data suitable for design calculations, including determination of tensile stiffness and strength at specified strains such as 2 %, 5 %, and 10 %.

Equipment and Data Processing

All procedures are performed on a calibrated universal testing machine with a load cell selected so that the measured force falls within the calibrated range, typically between 20 % and 80 % of capacity. Pneumatic or hydraulic grips with rubber-faced faces are used to prevent slippage without crushing the laminate, and contact or video extensometers are employed where accurate strain measurement is required. The final report states the standard used, specimen geometry, conditioning, test speed, individual and mean results for each direction, and the coefficient of variation, together with a description of the failure mode.

Applications

Tensile strength data for reinforced films support a broad range of engineering, quality control, and certification purposes:

• Construction: verification of reinforced vapor barriers, roofing underlayments, temporary enclosures, and scaffold sheeting against project specifications
• Packaging: qualification of FIBC liners, heavy-duty laminated sacks, and flexible packaging for safe working load calculations
• Agriculture: assessment of greenhouse films, silage covers, and hay wrap laminates for wind and snow load resistance
• Geotechnical engineering: design inputs for reinforced geomembranes, canal liners, and containment barriers based on wide-width tensile parameters
• Transportation and covers: strength validation for truck tarps, cargo covers, and marine covers subject to dynamic flapping loads
• Product development: comparison of scrim constructions, lamination adhesives, and resin formulations during material optimization
• Compliance and certification: demonstration of conformity with ISO, ASTM, EN, and GB specification limits for regulatory and buyer acceptance

FAQ

What is the difference between strip and grab tensile testing for reinforced films?

In the strip test, the entire specimen width is gripped and loaded, so all reinforcing yarns across the width share the load and the result reflects the full composite strength per unit width. In the grab test, only the central region of a wider specimen is loaded, which measures the strength contribution of the yarns directly in line with the grips and better simulates localized stress around attachment points. Most coated-fabric specifications rely on grab results, while design calculations favor strip or wide-width data.

Which standard should be used for a laminated scrim-reinforced PE tarpaulin?

For tarpaulin-type products, ASTM D751 or ISO 1421 is generally the most appropriate method, as these standards are written for coated and laminated fabrics where the textile reinforcement dominates. If only the film layer itself must be characterized, ISO 527-3, ASTM D882, or GB/T 1040.3 can be applied to the unfilled film. The choice should always follow the governing product specification or purchase agreement.

Why must reinforced films be tested in both machine and transverse directions?

Because the reinforcing scrim is usually cross-laid or woven with different yarn densities in each direction, the tensile strength and elongation can differ significantly between MD and TD. Testing only one direction can overestimate or underestimate the true load capacity of the laminate in service, so both directions are required for a valid characterization.

How does specimen conditioning affect tensile results?

Temperature and humidity influence the ductility of the polymer layers and, for hygroscopic fibers such as those used in some specialty laminates, the strength of the reinforcement itself. Conditioning at 23 °C and 50 % relative humidity ensures reproducible and comparable results; testing outside standard conditions requires the environmental state to be clearly reported.

What are common causes of invalid test results?

Frequent sources of error include specimen slippage in the grips, jaw breaks occurring at or near the grip faces, misalignment of yarns with the load axis, grips that crush the laminate at high clamping pressure, and incorrect load cell selection. Accredited third-party laboratories mitigate these issues through validated clamping fixtures, pre-test checks, and rejection criteria defined in the governing standards.