ASTM B406 – Transverse Rupture Strength of Cemented Carbides - PDF

ASTM B406 Compression Platens – Universal Grip Data Sheet (PDF)

Overview

ASTM B406 is the standard test method for the transverse rupture strength (TRS) of cemented carbides such as tungsten carbide–cobalt. A small ground bar is broken in three-point bending, and the stress in the bottom fibers at the moment of fracture is reported as the TRS. Because carbides are hard and brittle, TRS is the main strength property quoted on carbide grade data sheets and is used for grade comparison and lot acceptance in tooling, wear parts and dies.

Test Fixture Requirements

The test runs in a universal testing machine with a three-point fixture built to these dimensions:

• Supports: two ground cemented-carbide cylinders, 6.35 ± 0.02 mm (0.250 in) in diameter and at least 13 mm (0.5 in) long, with parallel axes.

• Support span: 14.3 ± 0.1 mm (0.563 in), center to center.

• Loading member: a cemented tungsten carbide ball of 10 ± 1.3 mm (0.4 in) diameter, or a ground carbide cylinder the same size as the supports, centered between them.

• Carbide (not hardened steel) contact surfaces are needed because a steel roller dents under the high local loads.

Specimen Requirements

• Thickness (h): 5.00 ± 0.25 mm (0.200 in)

• Width (b): 6.25 ± 0.25 mm (0.250 in)

• Length: at least 19.0 mm (0.750 in)

• Ground faces, with the four long edges chamfered or honed at 45° to no more than 0.25 mm (0.010 in). Grinding marks and edge chips start fractures, so surface finish matters.

• Test five specimens.

Test Procedure

1. Measure the width and thickness of each bar at mid-length with a micrometer.

2. Center the bar on the two support cylinders with a ground face down, square to the supports.

3. Center the ball or loading cylinder over mid-span.

4. Apply load at a rate no faster than 1.5 kN/s (350 lbf/s) until the bar breaks, and record the peak load.

5. Report the mean of the valid results and the standard deviation; state how many values were used if fewer than five.

TRS Calculation

TRS = 3PL ÷ (2bh²)

• TRS = transverse rupture strength (MPa or psi)

• P = load at fracture (N or lbf)

• L = support span, 14.3 mm (0.563 in)

• b = specimen width; h = specimen thickness

Example: a 6.25 mm wide, 5.00 mm thick bar breaks at 20,000 N. TRS = (3 × 20,000 × 14.3) ÷ (2 × 6.25 × 5.00²) = 858,000 ÷ 312.5 = 2,746 MPa (about 398 ksi).

Loads for strong grades reach roughly 20–30 kN, so a 50 kN universal testing machine is a good fit.

Related Standards

The following standards are similar to or used in conjunction with ASTM B406:

• ASTM B528 – Transverse rupture strength of sintered metal powder (PM) specimens

• ASTM C1161 – Flexural strength testing of advanced ceramics (also uses a three-point or four-point bend method)

• ASTM E290 – Bend testing of metallic materials (more for ductility than rupture strength)

• ISO 3327 – International standard for TRS of hardmetals, similar in scope and method to ASTM B406

Summary

ASTM B406 provides a clear, repeatable method to measure the transverse rupture strength of cemented carbides using a precise three-point bend setup. While it does not represent a material’s tensile or compressive strength, it serves as a valuable quality indicator for brittle, sintered materials like tungsten carbide. For manufacturers of tools, dies, and wear-resistant components, it is a vital part of the quality control process.

 

 

ASTM B406 FAQ

What is the support span in ASTM B406?

14.3 ± 0.1 mm (0.563 in) between the centers of two 6.35 mm (0.250 in) cemented-carbide support cylinders.

What size is the ASTM B406 test specimen?

A ground bar 5.00 ± 0.25 mm thick, 6.25 ± 0.25 mm wide and at least 19.0 mm long, with the long edges chamfered or honed to no more than 0.25 mm.

How is transverse rupture strength calculated?

TRS = 3PL ÷ (2bh²), where P is the fracture load, L the span, b the width and h the thickness. A 20,000 N fracture load on a standard bar gives about 2,746 MPa.

What loading rate does ASTM B406 use?

Load no faster than 1.5 kN/s (350 lbf/s) until the specimen breaks.