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Bending Testing

Bending testing is a core mechanical test that evaluates a material’s flexural strength, ductility, and resistance to fracture under static bending loads. It’s widely used for brittle or semi-brittle materials (e.g., metals, plastics, ceramics) and structural components.

UnitedTest Popular Bending testing machine

Feature:

  • Computer control hydraulic servo
  • Imported oil pump and servo motor

Key parameter:

  • Load: 500KN/1000KN
Details

Metal Bending & Rebending Testing Machine

Model: UT1017A, ISO 7438, ASTM E290

Feature:

  • Computer control hydraulic servo
  • Bending and rebending

Key parameter:

  • Load: 400KN
Details

Steel Pipe Bending Testing Machine

Model: GGW-60H, ISO 8491

Feature:

  • ISO 8491, ISO 5173, ASTM A370
  • Bending and rebending

Key parameter:

  • Max. diameter: 60mm
  • Bending angle: 0°-90°
Details

Feature:

  • ASTM C1550
  • Oil cylinder at topside
  • Large stroke 200mm piston

Key parameter:

  • Load: 1000KN
  • Deformation range: 90mm
Details

Feature:

  • ISO 6935-2
  • Rebar repeat bending

Key parameter:

  • Forward: 0°-180°
  • Backward: 0°-90°
  • Max. sample diameter: 40mm
Details

Optical Fiber Cable Warp Bending Testing Machine

Model: UTOF35-WB, IEC 60794-1-21 Method E11: Bend Test

Feature:

  • IEC 60794-1-21 Method E11: Bend Test
  • optical cables wrapping bendding test

Key parameter:

  • Driving wheel diameter: 200mm, 300mm, 400mm
  • Winding speed: 1-10 cycles per minute
Details

What's the bending test?

Bending testing is a core mechanical test that evaluates a material’s flexural strength, ductility, and resistance to fracture under static bending loads. It’s widely used for brittle or semi-brittle materials (e.g., metals, plastics, ceramics) and structural components.


Bending Test Principle: 

Bending testing applies a three-point or four-point bending load to a standardized specimen, causing it to deform (elastic then plastic) until fracture or a specified deflection. The key principle is stress distribution across the specimen cross-section:

The outer surface of the bent specimen is in tension, the inner surface in compression, and the neutral axis (center) has no stress.

The test measures the maximum bending stress (flexural strength) the material can withstand before failure, or its deflection at a given load (reflecting ductility).


How the Bending Test Works? 


Step 1: Specimen PreparationFabricate specimens to standard dimensions (e.g., rectangular bars for metals/plastics, prisms for concrete). Common sizes: 10mm×10mm×100mm (metals) or 40mm×40mm×160mm (cement mortar).Ensure the specimen surface is smooth, free of cracks or defects, and the cross-section is uniform.


Step 2: Test SetupChoose between two common loading methods:

Three-point bending: Place the specimen on two supports (span L), apply a single load at the midpoint. Simple setup, widely used for general materials.

Four-point bending: Place the specimen on two supports, apply two symmetric loads (equidistant from each end). Creates uniform bending stress in the middle section, ideal for brittle materials (avoids stress concentration).


Step 3: Loading & Data Collection

Apply load at a constant rate (specified by standards, e.g., 2mm/min for metals, 0.5mm/min for plastics) using a universal testing machine.Record the load-deflection curve in real time—tracks how the specimen deforms under increasing load.


Step 4: Calculation of Key Indicators

Flexural strength (σf): Maximum bending stress before fracture, calculated as:

Three-point bending:    90a1667d-d988-477f-949a-380eb549e85a.png (where F = maximum load, L = span, b = specimen width, h = specimen height). 

Four-point bending:    cfbd93fe-a69c-4ad4-a5a2-6c1599e97c94.png

Flexural modulus (Ef): Stiffness of the material, derived from the linear elastic segment of the load-deflection curve.Deflection at fracture: Indicates ductility—larger deflection means better resistance to brittle fracture.


Main Applications

Bending testing is critical for materials and industries where flexural performance affects service safety:


  • Metals & Alloys: Steel bars, aluminum profiles, automotive chassis components. Tests ensure they can withstand bending loads during installation or use.

  • Plastics & Composites: Plastic pipes, fiber-reinforced composites (e.g., carbon fiber parts), electronic device casings. Evaluates flexibility and impact resistance.

  • Construction Materials: Concrete beams, cement mortar, bricks, stone slabs. Verifies load-bearing capacity in structural bending scenarios (e.g., floor slabs, bridges).

  • Ceramics & Glass: Ceramic tiles, glass panels, refractory materials. Assesses brittleness and resistance to breakage under bending.

  • Quality Control & R&D: Validates production processes (e.g., heat treatment of metals, fiber mixing in composites) and develops new materials with targeted flexural properties.

ISO & ASTM Standards

ISO Standards

  • ISO 178:2019: Plastics — Determination of flexural properties. Covers three/four-point bending for plastics, specifies specimen dimensions and loading rates.

  • ISO 7438:2016: Metallic materials — Bend test. For metal sheets, strips, and bars, defines bending angles and acceptance criteria for ductility.

  • ISO 679:2019: Cement — Determination of strength. Includes bending test for cement mortar prisms (40mm×40mm×160mm).

  • ISO 15630-1:2019: Steel wire — Bending test. Specifies bending procedures for steel wires used in construction or machinery.

ASTM Standards

  • ASTM D790-23: Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials. Core standard for plastic bending testing.

  • ASTM E290-23: Standard Test Methods for Bend Testing of Metallic Materials. Covers bend tests for metals to evaluate ductility and bending strength.

  • ASTM C348-22: Standard Test Method for Flexural Strength of Hydraulic Cement Mortars. Bending test requirements for cement mortar.

  • ASTM C1161-18: Standard Test Method for Flexural Strength of Advanced Ceramics at Ambient Temperature. For ceramic materials’ bending performance.


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