Whole-Tube Tensile Strength Testing Method: Principles, Standards, and Procedures

Whole-tube tensile strength testing evaluates the tensile performance of tubing in its complete, as-manufactured form, making it an essential quality control method for medical catheters, heat-shrinkable sleeving, and polymer hoses. This article explains the testing principles, applicable international standards, specimen preparation, test procedures, and result evaluation. It serves as a practical technical reference for manufacturers, quality engineers, and accredited third-party laboratories.

Technical Overview

Whole-tube tensile strength testing, also known as full-section or integral-tube tensile testing, is a mechanical test in which a complete length of tubing is gripped at both ends and pulled to failure along its longitudinal axis. Unlike tests on die-cut dumbbell or strip specimens, whole-tube testing preserves the original geometry of the product, including extrusion weld lines, seam welds, wall thickness distribution, molecular orientation, and bonded joints such as catheter hub-to-tube connections.

The method is widely applied to products whose structural integrity depends on the complete tubular cross-section, including single-use intravascular catheters covered by ISO 10555-1, infusion and transfusion tubing covered by the ISO 8536 series, heat-shrinkable sleeving covered by ASTM D2671 and UL 224, flexible insulating sleeving covered by IEC 60684-2, and elastomeric tubing evaluated with reference to ISO 37 and ASTM D412. For thermoplastic pipes, longitudinal tensile properties are determined according to ISO 6259 or GB/T 8804, and in small-diameter products whole-section specimens are frequently used.

The primary outputs of the test are the maximum tensile force, the calculated tensile strength based on the cross-sectional area, the elongation at break, and the failure mode. These results support design validation, incoming material inspection, batch release, sterilization and aging studies, and regulatory submission.

Testing Samples

Medical Catheters and Interventional Tubing

Typical samples include central venous catheters, peripheral catheters, urethral catheters, epidural catheters, drainage tubes, and extension lines. Specimens are tested either as the tube alone or as the complete hub-tube assembly to verify bond strength in accordance with ISO 10555-1 and related medical device standards.

Heat-Shrinkable and Insulating Sleeving

Polyolefin, PVDF, silicone rubber, and PTFE sleeving used for wire insulation and harness protection are tested in the expanded, as-supplied state. Product performance requirements are defined in ASTM D2671, UL 224, and IEC 60684-2, which specify minimum tensile strength and elongation at break.

Rubber and Thermoplastic Hoses and Tubing

Silicone, PVC, TPU, latex, and nylon tubing used in medical, food, and industrial applications can be tested as full sections. Elastomeric materials are commonly evaluated using methods aligned with ISO 37 and ASTM D412, adapted to tubular specimens.

Thermoplastic Pipes

Small-diameter PVC, PE, and PP pipes may be tested using whole-ring or whole-section specimens, while larger pipes generally use longitudinal strips cut from the pipe wall in accordance with ISO 6259 and GB/T 8804. The choice depends on pipe diameter, wall thickness, and the governing product standard.

Testing Items

• Ultimate tensile force and tensile strength of the whole tube section.
• Elongation at break and, where required, tensile stress at specified elongation.
• Bond or joint strength between the tube and hubs, connectors, or tips.
• Failure mode classification, such as tube breakage, bond separation, or grip-line fracture.
• Yield behavior and force-displacement curve characteristics for thermoplastic materials.
• Comparison of tensile properties before and after sterilization, thermal aging, or shelf-life conditioning.

Testing Methods

Specimen Preparation

Representative tube sections are cut to a length that provides sufficient grip engagement plus the required gauge length, typically at least 150 mm for small-diameter tubing or the length specified in the applicable standard. Cut ends must be clean, square, and free from burrs, cracks, or crushing marks that could cause premature failure. Unless otherwise specified, specimens are conditioned in a standard laboratory atmosphere of 23 ± 2 °C and 50 ± 5 % relative humidity in accordance with ISO 291 or ASTM D618 before testing.

Dimensional Measurement and Cross-Sectional Area

The outer diameter, inner diameter, or wall thickness is measured at several positions along the specimen using calibrated instruments such as a laser gauge, optical comparator, or pin gauge. The cross-sectional area is then calculated as A = π/4 × (D₀² − Dᵢ²), where D₀ is the mean outer diameter and Dᵢ is the mean inner diameter. Accurate dimensional data are critical because tensile strength is derived from this area.

Equipment and Fixturing

Testing is performed on a universal testing machine calibrated in accordance with ISO 7500-1 or ASTM E4, equipped with a load cell selected so that the expected breaking force falls within a suitable range of the capacity, commonly 20 % to 90 %. Grip selection is decisive for whole-tube testing: pneumatic side-action grips, wedge grips, or capstan-type wrap grips are used to prevent slippage and jaw breaks. For thin-walled or soft silicone tubing, smooth metal mandrels or reinforced liners may be inserted into the tube ends to distribute gripping pressure and avoid crushing. Catheter assemblies with hubs require custom adapters that clamp the hub securely while leaving the bond region unstressed by the fixtures. Elongation is measured with a contact or video extensometer, or from crosshead separation when permitted by the standard.

Test Procedure

• Verify machine calibration, grip alignment, and load cell zero before mounting the specimen.
• Mount the specimen axially in the grips with the marked gauge length centered, applying a small preload to remove slack without elongating the sample.
• Set the gauge length and crosshead speed according to the governing standard, for example 200 mm/min is commonly specified for catheter assembly tests per ISO 10555-1, while elastomeric tubing is often tested at approximately 500 mm/min per ISO 37 and ASTM D412.
• Start the test and pull the specimen to complete rupture at constant speed, recording the force-extension curve continuously.
• Note the peak force, force at break, extension at break, and the exact location and mode of failure.
• Repeat the test on the required number of specimens, typically a minimum of three to five per condition, and retest any specimen that fails by slippage or jaw break.

Data Calculation and Evaluation

Tensile strength is calculated by dividing the maximum force by the original cross-sectional area, expressed in MPa. Elongation at break is calculated as the increase in gauge length at rupture divided by the original gauge length, expressed as a percentage. For bond and assembly tests, the result is reported directly as peak force in newtons and compared with the minimum force specified in the product standard, such as the size-dependent requirements of ISO 10555-1. The test report should include specimen identification, dimensions, calculated area, conditioning details, gauge length, test speed, individual and mean results, standard deviation, and failure mode description.

Applications

Whole-tube tensile testing is used across the product lifecycle in several key scenarios:

• Design verification of medical catheters and proof of hub-tube bond integrity for regulatory submissions.
• Bulk release testing of heat-shrinkable sleeving to demonstrate compliance with UL 224 and IEC 60684-2 requirements.
• Incoming inspection of purchased tubing and hoses in medical device and automotive manufacturing.
• Extrusion process control to detect weld-line defects, material contamination, or wall thickness variation.
• Stability and validation studies comparing tensile properties after ethylene oxide sterilization, gamma irradiation, steam autoclaving, or accelerated aging.
• Failure analysis of returned or field-failed tubing to identify root causes such as material degradation or bond weakness.

FAQ

Why test the whole tube instead of a cut dumbbell specimen?

Whole-tube testing evaluates the product exactly as manufactured and as used. It captures seam and weld-line quality, circumferential wall uniformity, and joint strength, none of which are represented by a flat die-cut specimen. For catheters and sleeving, most product standards explicitly require testing of the complete tube or assembly.

How can slippage and jaw breaks be prevented?

Use grips with sufficient pressure but smooth faces, increase grip contact length, insert mandrels or liners into the tube ends, align the specimen precisely along the load axis, and ensure the free gauge length is long enough that failure occurs away from the grips. Any failure at the grip line should be recorded and the specimen retested.

Which cross-sectional area should be used for strength calculation?

The original cross-sectional area of the tube wall, calculated as π/4 × (outer diameter squared minus inner diameter squared), measured on the untested specimen. Using nominal catalog dimensions instead of measured dimensions can introduce significant error, particularly for thin-walled tubing.

What crosshead speed should be selected?

The speed must follow the governing product or material standard. Catheter assemblies per ISO 10555-1 are commonly tested at 200 mm/min, elastomeric tubing per ISO 37 and ASTM D412 at approximately 500 mm/min, and rigid thermoplastic tubing at lower speeds in the range of 5 to 50 mm/min. When no standard specifies a speed, it should be documented and kept constant for all comparative testing.

How many specimens are required for a valid test?

Most standards require a minimum of three to five specimens per sample condition. Results are reported as individual values together with the mean and standard deviation. Specimens failing by grip slippage are excluded and replaced so that the reported statistics reflect true material behavior.

Can braided or reinforced tubing be tested with this method?

Yes. Reinforced tubing can be tested as a full section to evaluate the composite structure, but the test report should describe the reinforcement construction, and failure modes should be interpreted carefully because the load is shared between the liner, braid, and jacket. Mandrel use requires extra caution to avoid damaging the inner liner.