Mechanical test

The mechanical tests are experiments of which the goal is to characterize the laws of behaviors materials (Mécanique of the continuous mediums). The law of behavior establishes a relation between the constraints (pression=force/surface) and the deformations (unit lengthening without dimensions). One should not confuse a deformation with a displacement or a dilation.

However, the deformation of a part depends on the form of the part and the way in which the external efforts on this part are exerted. The tests thus should be standardized. Standards thus define:

• the shape of the part whose the material is made; one speaks about standardized test-tube ;
• How the efforts on the test-tube are exerted; one speaks about test standardized .

Uniaxial traction

See also: Test tensile

Principle

The test-tube is held in two points (by a grip or a hook), connected to ropes. The test-tube is then stretched at constant speed, and one raises the force of traction necessary according to lengthening. These tests make it possible to plot a curve known as of traction from which the following characteristics can be deduced:

• elastic strain according to the force applied from where one can deduce, knowing dimensions of the test-tube, the Modulus Young;
• the often noted yield stress R_e, or elastic limit to 0,2% R_e0,2;
• plastic deformation;
• tensile strength or stress breaking often noted R_m, which is the Contrainte maximum attack in the course of tests.

According to material, the Temperature and the Speed of deformation, the curve can have various forms.

Nominal or apparent characteristics

• Limit elastic: $R\_\; \{E\}\; =\; \backslash \; frac\; \{F\_\; \{E\}\}\; \{S\_0\}$

• Tensile strength: $R\_\; \{m\}\; =\; \backslash \; frac\; \{F\_\; \{m\}\}\; \{S\_0\}$
• Elongation at fracture: $A\; \backslash \; \%\; =\; 100\; \backslash \; cdot\; \backslash \; frac\; \{L\_f\; -\; L\_\; \{O\}\}\; \{L\_o\}$

In this expression, $L\_o$ and $L\_f$ are respectively the initial lengths and finales after rupture.

• Constriction with the rupture: $Z\; \backslash \; \%\; =100\; \backslash \; cdot\; \backslash \; frac\; \{S\_o-S\_f\}\; \{S\_o\}$

In this expression, $S\_o$ and $S\_f$ are respectively the initial sections and finales after rupture.

• Modulus Young, represented by the slope of the curve in its linear part: $E=\; \backslash \; frac\; \{D\; \backslash \; sigma\}\; \{D\; \backslash \; epsilon\}$.
• Poisson's ratio: $\backslash \; naked\; =\; \backslash \; frac\; \{\backslash \; left\; (d\_\; \{O\}\; -\; D\; \backslash \; right)/d\_\; \{O\}\}\; \{\backslash \; left\; (L-L\_\; \{O\}\; \backslash \; right)/L\_\; \{O\}\}$

where $d\_o$ and $d$ are respectively the initial diameter and the diameter under load, $L\_o$ and $L$ the initial length and the length under load. $\backslash \; nu$ is defined in the elastic range.

The values above are called apparent or conventional (in English engineering strain and engineering stress), because they refer to the initial section of the test-tube. The values known as true or rational (in English true strain and true stress), are also calculated, based on the sections actually measured with lengthening considered. Starting from these actual values, a traction diagram known as rational is plotted. This curve highlights the phenomenon of work hardening.

See also: Effect Portevin-Lechatelier, Cloud of Cotterel.

Standards

• European (CEN)

* IN 10002-1: Metallic materials - tensile Test - part 1: testing method to room temperature.

* IN 10002-5: Metallic materials - tensile Test - Part 5: testing method to high temperature.

• International (ISO)

* ISO 6892: Metallic materials - tensile Test to room temperature.

* ISO 10618: Carbon fibers - Determination of the properties in traction on resin wire impregnated.

• American (ASTM)

* ASTM E8: Standard test methods for tension testing off metallic materials. (there exists standard ASTM E8M which is the metric version).

* ASTM E21: Standard methods for elevated temperature tension tests off metallic material.

Uniaxial pressing

Isostatic pressing

Shearing

shear test orthoradial

Impact strength

The impact test is a complement with the tensile test. It is a question of breaking in only one blow a notched sample in order to measure energy necessary to carry out this rupture. This test is carried out on a pendulum sheep (example: Sheep Charpy).

Types of tests

* Test deflection per shock on notched sample Charpy

*Essai of inflection by shock Izop

Normalizes

• American

* ASTM E23: Standard test methods for notched bar impact testing off metallic materials.

• European:

* IN 10045-1: Metallic materials - deflection Test per shock on Charpy test-tube - Part 1: testing method.

* IN 10045-2: Metallic materials - deflection Test per shock on Charpy test-tube - Part 2: checking of the testing machine (pendulum hammer).

Hardness

Types of tests

Minerals:

* Mohs

Metals:

* Vickers tests HV, Brinell HB, Rockwell HR

Rocks:

* Shore,

See also:
Ductility

Standards

• International (ISO) and European (CEN)

* IN ISO 2039-2: Plastics - Determination of hardness - Part 2: Rockwell hardness.

* IN ISO 6506-1: Metallic materials: test Brinell hardness - Part 1: testing method.

* IN ISO 6507-1: Metallic materials - Test Vickers hardness - Part 1: testing method

* IN ISO 6508-1: Metallic materials: test Rockwell hardness Left 1: testing method (scales has, B, C, D, E, F, G, H, K, NR, T).

• American

* ASTM E10: Standard method for Brinell hardness off metallic materials.

* ASTM E18: Standard methods for Rockwell hardness and Rockwell superficial hardness off metallic materials.

* ASTM E140: Standard hardness conversion tables for metal.

Inflection

Inflection three points and four points

Tire

The fatigue test consists in applying to a part an alternate variable load (average of the pressures applied is null) or repeated (average of the pressures applied is nonnull). It will try as well as possible to reproduce the conditions of operating of the part.

The ruptures by tiredness are primarily associated with the full number of applications of a load and not with the time of service or the age of the part. The rupture by tiredness does not give any preliminary sign before breaking, this is why it can very often surprise the user.

External bonds

• Soudeur.com the site gate of the welder and the trades of welding
• Mechanical test and Test-tubes

Random links:

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