Ensayo de tracción | 87/93 | UPV

Introduction and Overview of Tensile Test

In this section, Professor David García Sanoguera introduces himself and outlines the topics to be covered in the presentation, focusing on the tensile test, different types of efforts, test regulations, and the test machine.

Types of Efforts in Materials Testing

• The tensile test covers tension as one of the primary types of efforts in materials testing.

• Other types include compression, flexure, and shear.

• Regulations such as UNE 10002 for metallic materials and UNE-EN-ISO 527 for plastics govern these tests.

Requirements for Test Machine

• The test machine must reach the force required to break the specimen.

• It should control deflection speed and record applied force and specimen deflection.

• Components include clamps with springs or conical shapes, a load cell for measuring force, and a data acquisition system.

Regulations and Test Specimen Details

This part delves into specific regulations governing different material types in the tensile test. It also discusses requirements for the test machine components like clamps and load cells.

Regulations for Tensile Testing

• Various regulations exist such as UNE 10002 for metallic materials.

• Different standards apply to materials like plastics (UNE-EN-ISO 527) and elastomers (UNE 53510).

Test Machine Components

• Key components include clamps with varying designs (springs or conical shape).

• A load cell measures applied force while a data acquisition system records all necessary data.

Test Specimen Preparation and Breakage

This section focuses on the preparation of test specimens according to regulations to ensure proper breakage within specified marks during testing.

Test Specimen Requirements

• Size and shape are dictated by regulations even if not standard.

• Breakage must occur within marked zones on specimens regardless of their shapes (rectangular or circular).

Ensuring Breakage Within Marks

• All specimens feature an 'I' shape design to ensure breakage at a specific point.

Operational Process of Tensile Testing

Here, Professor García explains the operational process involved in conducting a tensile test from placing the specimen in clamps to logging force vs. elongation data.

Operational Steps

• Place the specimen in clamps followed by applying tension at a constant speed.

Analysis of Force vs. Elongation Chart

This part discusses how force vs. elongation charts are generated during tensile testing along with observations regarding specimen behavior under increasing loads.

Observations from Force vs. Elongation Chart

• Initial conservation of size before elongation occurs under applied forces.

Transition to Stress vs. Strain Analysis

Transitioning from force vs. elongation charts to stress vs. strain analysis is explained here along with definitions of stress and strain.

Stress vs. Strain Analysis

-Stress defined as applied force divided by initial surface area; strain defined as elongation divided by initial length.

Elastic Area & Plastic Area Analysis

Detailed examination of elastic area characterized by linear stress-strain relationship contrasted with plastic area where permanent strains occur beyond elastic limits.

Elastic Area Characteristics

• Linear relationship between stress and strain defines elastic modulus or Young's modulus.

[Plastic Area Behavior]

• Beyond elastic limit, no proportional relationship exists between stresses applied and strains produced.

Tensile Test and Mechanical Properties Analysis

In this section, the speaker discusses the properties obtained from a tensile test on materials, including stress at break, strain at break, necking, and tenacity.

Stress at Break and Strain at Break

• Stress at break is defined as the maximum stress a material can withstand.

• Strain at break is the relative elongation of the material until it breaks.

• The strain at break can be calculated by subtracting the initial length from the final length, dividing by the initial length, and multiplying by 100%.

Necking and Section Reduction

• Necking measures the reduction in section of a material.

• It is determined by comparing the initial section with the final section after breakage.

Area Under Tensile Curve and True Stress vs. True Strain Chart

• The area under the tensile curve indicates absorbed energy during testing, reflecting material tenacity.

• The true stress vs. true strain chart considers changes in specimen length and section during testing to provide accurate data.

• Expressions correlating conventional stress with true stress are discussed for accurate analysis.

Regulation and Main Properties Obtained

This part covers regulations governing tests and specimens used, along with key properties obtained such as elastic limit, elastic modulus, stress at break, strain at break, necking, and tenacity.

Regulation Compliance

• A regulation governs test procedures and specimen selection for consistency in results.

Key Properties Obtained

• Elastic limit signifies material deformation limits under load.

• Elastic modulus reflects material stiffness.

• Stress at break denotes maximum supported stress before failure.

• Strain at break measures relative elongation until fracture occurs.

• Necking quantifies section reduction post-breakage.