Footwear Flexing Test – Tested by SATRA TM92 Method

The SATRA TM92 test method focuses on the flexing resistance of completed footwear. Footwear flexing test requirements differ among regional standards. The SATRA TM92 method evaluates whole‑shoe flex durability by repeated bending around the shoe’s natural flexing line. Bending angle can be adjusted from 30° to 90°, with typical test speed ranging from 60‑230 rpm depending on angle settinggester-ppe.... Laboratory ambient condition is normally controlled at 23 ± 2 °C for sample conditioning and testing.

The whole‑shoe flexing test is a common method in the footwear industry. It checks how well finished shoes resist repeated bending fatigue. It mimics real‑life walking flexing motion to test how footwear performs during end‑use. In the test, complete shoe specimens are secured in fixtures and subjected to reciprocating bending cycles under controlled conditions. This cyclic flex simulates repeated foot bending during walking. This motion ensures flex stress concentrates along the footwear’s natural flex line to reproduce in‑service damage modes.

Terminology Relating to Footwear (SATRA STM‑101)

Flexing Machine‑Water Penetration Test (SATRA TM77)

Footwear General Test Conditions (ISO 18895)

Test Method for Flex Resistance of Completed Footwear (ISO 24266 Method A)

Footwear‑Test Methods for Outsoles, Uppers, Linings and Insocks (ISO 22649)

1.1 Flexing Cycle

In footwear flexing testing, one flexing cycle means the footwear specimen completes one full back‑and‑forth bending movement through the defined test angle and returns to its starting neutral position.

‑ The flexing cycle relies on the machine’s reciprocating movement and the testing standards used. It generates repeated bending stress on the shoe upper, sole and bonding seams. Damage such as sole cracking, upper crease rupture or joint separation may accumulate after a large number of cycles.

1.2 Natural Flexing Line

The natural flexing line is the anatomical bending position of footwear corresponding to the metatarsal joint of human feet. During testing, bending rotation must align with this line to realistically reproduce flex stress that occurs when people walk.

‑ Related to the whole‑shoe flexing tester, the natural flexing line position is adjusted via front toe press‑block fixture placement for each shoe size and shape.

1.3 Reciprocating Movement

One complete back‑and‑forth bending driven by the machine swing plate counts as one flexing cycle.

The instruments and consumables used are as follows:

2.1 Whole‑Shoe Flexing Tester

Model GT‑KA01‑2 series, supports adjustable bending angle 0‑90°, equipped with acrylic protective safety cover, heel fixture adopting linear slide structure for low‑resistance smooth movement, touch‑screen parameter setting and preset cycle auto‑stop functiongester-ppe.... Two variants are available: GT‑KA01‑2A for four specimens tested simultaneously; GT‑KA01‑2B for two specimens tested simultaneously.

2.2 Adjustable Toe Press‑Block Assembly

Position‑adjustable clamping fixture to hold the shoe toe area, ensures bending occurs along the footwear natural flexing line. Interchangeable pressure pads fit different shoe shapes and sizes.

2.3 Artificial Foot Supports (Optional)

Adjustable‑size internal foot forms, used to maintain footwear original shape inside during flexing for certain shoe types.

2.4 Apparatus for Footwear Damage Evaluation

Adequate laboratory ambient lighting for visual inspection. Operators can observe specimens and record crack, rupture or delamination after preset flex cycles.

2.5 Reference Control Footwear Specimens

Reference shoes with known flex‑failure cycle counts are used to verify instrument stability. There is no universal global reference footwear standard; laboratories prepare control specimens matched to their equipment and test parameters.

2.6 Damage Assessment Criteria

2.6.1 Reference Failure Specimens

Series of pre‑tested whole‑shoe specimens showing typical flex‑induced defects (sole cracking, upper tearing, bond separation). Keep reference specimens stored under standard laboratory atmosphere to retain original damage appearance.

2.6.2 Visual Assessment Checklist

Recordable defect categories: no damage, slight creasing, minor surface crack, obvious crack, material rupture, seam opening, sole‑upper bond delamination.

2.6.3 Digital Recording System

Digital camera or imaging system to capture specimen surface condition after each inspection interval.

2.7 Shoe Size Measurement Tools

Ruler and calipers for measuring footwear outer dimension to set fixture positions correctly.

2.8 Temperature‑Controlled Conditioning Chamber (if required)

For low‑temperature flexing tests.

The footwear flexing resistance test method  relies on lab equipment as its main support. It reveals flex‑induced damages such as sole cracking, upper tearing and joint separation that footwear faces with normal walking use. The complete shoe goes onto the whole‑shoe flexing tester. The test specimen is fixed between the heel swing fixture and front toe press‑block. It undergoes repeated reciprocating bending around the shoe’s natural flexing line under preset angle and cyclic speed. This cyclic bending continues for a pre‑set number of cycles. After reaching scheduled cycle intervals, operators inspect footwear for visible damage. They compare observations against assessment checklists and reference specimens. Flexing performance is reported by recording cycle numbers at first‑occurrence of defined damage or by damage condition after target total cycles.

4.1 Basic Sampling Unit

Consider production batches or finished‑shoe product lots as the basic sampling unit.

4.2 Laboratory Sampling Unit

Select finished‑shoe pairs randomly from the basic production lot. Avoid samples with pre‑existing visual defects such as scratches, cracks or incomplete bonding.

4.3 Flexing Resistance Test Samples: Selection, Quantity, and Preparation

4.3.1 Condition test samples unless noted otherwise. Conditioning parameters follow agreed‑upon specification or corresponding product standard.

4.3.2 The lab staff should take at least two complete finished shoes from each lab sampling lot for flexing testing.

4.3.3 Follow these sampling principles:

Samples should represent actual production product.

For multi‑size product lines, select critical representative sizes.

Ensure each test specimen has no pre‑manufacturing damage.

Avoid selecting shoes with visible surface flaws.

Unless stated otherwise, condition samples under laboratory atmosphere of 23 ± 2 °C for minimum 4 hours before mounting onto tester.

5.1 Condition the sample for at least 4 hours. It should be in standard laboratory conditions for footwear testing: 23 ± 2 °C.

5.2 All flexing resistance testing procedures must follow agreed‑upon laboratory environmental conditions.

5.3 Adjust machine eccentricity setting to achieve required bending angle (commonly 30°, 45°, 50°, 60° or 90°) according to product specification or contract requirement. Secure test shoe onto machine: place shoe heel part into the heel swing fixture, adjust front toe press‑block position so pressure acts upon shoe toe region and bending aligns with shoe natural flexing line.

5.4 Set test speed within machine adjustable range according to standard requirement. Reset digital counter to zero and input preset target flex cycles. Close acrylic safety protective cover.

5.5 Start the instrument. The tester runs reciprocating flex cycles and will auto‑stop upon reaching preset cycle value. After finishing each preset cycle interval, open safety cover and take out or inspect specimen for damage. Record observations according to Section 6 assessment rules. Continue testing until target total cycles or until defined failure damage appears.

6.1 Take the test footwear out from fixture for visual inspection under adequate lighting.

6.1.1 Use visual assessment checklist and reference footwear specimens. Inspect sole, upper material and bonding seams. The assessment items are as follows:

For Sole / Upper Material Damage:

‑ No damage: No visible crease, crack or rupture

‑ Slight creasing: Obvious crease without surface cracking

‑ Minor surface crack: Fine superficial crack only

‑ Obvious crack: Deep penetrating crack on material

‑ Material rupture: Complete tearing through material thickness

For Bond & Seam Performance:

‑ No separation: Seam and sole‑upper bond remain intact

‑ Slight opening: Minor local seam gap

‑ Serious delamination: Large‑area bond separation or seam tearing

6.1.1.1 If intermediate status appears between two assessment categories, clearly describe the actual observed condition in test report.

Note: For arbitration tests, inspection shall be completed by at least two qualified assessment personnel. Maintain consistent inspection criteria to guarantee valid test results.

6.1.2 Use the assessment criteria as agreed upon by both the buyer and seller.

6.1.3 Record cycle number when first defined failure occurs, or record damage status after completing total target cycles. Calculate summary test results for each specimen and the testing batch.

SATRA TM77

Flexing Machine‑Water Penetration Test

ISO 24266

Footwear‑Test Methods for Whole Shoe Flexing Resistance

HG/T 2871‑2022 Method B

Footwear‑Test Method for Whole‑Shoe Flexing Resistance

ISO 18895

Footwear‑Standard Atmospheres for Conditioning and Testing

ISO 22649

Footwear‑Test Methods for Outsoles, Uppers, Linings and Insocks