Standard Test Method for Tear-Propagation Resistance (Trouser Tear) of Plastic Film and Thin Sheeting by a Single-Tear Method - PDF

 

ASTM D1938 measures the tear-propagation resistance of plastic film and thin sheeting, 1 mm (0.04 in) thick or less, with a single-tear "trouser" specimen. A strip is slit lengthwise so it looks like a pair of trousers; the two legs are pulled apart in a tensile machine and the average force needed to keep the tear running is recorded. It is used for packaging film, bags, liners and thin sheet.

Trouser Specimen

• 25 mm (1 in) wide × 75 mm (3 in) long

• A 50 mm (2 in) slit cut along the center line from one end, leaving two 12.5 mm wide legs and 25 mm of uncut material

• Thickness: 1 mm or less; measure it in the area to be torn

• Cut specimens in both the machine and transverse directions; test at least 5 in each

• Condition at 23 °C and 50% RH for at least 40 h (ASTM D618)

Test Procedure

• Clamp one leg in each grip with the legs in line, so the tear runs straight down the center

• Set the initial grip separation to the leg length

• Pull at 250 mm/min (10 in/min)

• Record force over the whole tear; discard specimens where the tear runs off to the side

Calculations

Tear-propagation force = average force over the tear (N or lbf), ignoring the start-up peak

Tear resistance = average tearing force ÷ thickness (N/mm), when specimens of different thickness are compared

Example: a 25 µm (0.025 mm) LDPE film tears at an average of 0.42 N in the machine direction. Tear resistance = 0.42 ÷ 0.025 = 16.8 N/mm.

Equipment

• Universal testing machine with a low-capacity load cell (10–50 N) for thin films

• Light pneumatic or vise grips with rubber-faced jaws that grip film without cutting it

• Slitting template or die for consistent 50 mm slits

Related Standards

• ASTM D1922 – Elmendorf (pendulum) tear of film

• ASTM D1004 – tear initiation of film and sheeting

• ASTM D624 – tear strength of rubber

• ASTM D2261 – tongue tear of fabrics

• ISO 6383-1 – trouser tear of film and sheeting

ASTM D1938 FAQ

What size is the ASTM D1938 trouser specimen?

25 mm wide × 75 mm long, with a 50 mm slit cut down the center from one end.

What test speed does D1938 use?

250 mm/min (10 in/min).

What thickness range does D1938 cover?

Plastic film and sheeting 1 mm (0.04 in) thick or less.

What is the difference between D1938 and D1004?

D1938 measures the force to keep a tear running from a pre-cut slit (propagation). D1004 uses a 90° notched specimen to measure the force to start a tear (initiation).