اختبار الشد الثابت المحوري

Axial Static Tension

• This chapter studies how to perform an axial static tension test on a metal sample.
• It analyzes the relationship between load and elongation.
• It introduces three loading zones: elastic, elastic-plastic, and plastic.
• It calculates various mechanical properties of the tested metal sample.
• It aims to develop the student's ability to discuss and interpret these properties accurately.
• Axial static tension involves applying a load along the axis of the sample.
• The load increases gradually until failure.
• The sample is typically cylindrical with a circular cross-section, or prismatic with a square or rectangular cross-section.
• This test is crucial for controlling the quality of metal materials and determining properties like the proportional limit stress, yield stress, ultimate tensile strength, modulus of elasticity, and resilience.

Mechanical Properties Under Axial Static Tension Load

• When a metal rod (cylindrical or prismatic) is subjected to axial static tension, elongation occurs.
• Elongation increases with increasing load.
• Assuming a constant cross-sectional area (A) and a measurement length (L). The load (P) and corresponding elongation (AL) are considered at any point during loading.
• Stress (F) is calculated as F=P/A.
• Strain (e) is calculated as e=AL/L.
• The stress-strain relationship for a ductile metal (e.g., mild steel) is divided into three zones.

Stress-Strain Relationship for Ductile Metals

• Elastic Zone: Strain is proportional to stress (linear).
• Elastic-Plastic Zone: Beginning after the linear part, ending at the ultimate stress.
• Plastic Zone: From the ultimate stress to the fracture of the sample.

Mechanical Properties in the Elastic Region

• Proportional Limit Stress: The stress at which the material begins to transition from the elastic to the plastic region. The stress at the end of the straight-line portion on the stress-strain curve.
• Elastic Limit Stress: The maximum stress a material can withstand without permanent deformation upon stress removal. It's located on the stress-strain curve at point 'b'.
• Yield Stress: The stress at which significant strain occurs with little or no increase in stress. It has two types: a maximum and a minimum. The maximum is located on the curve at point 'c' and depends on the testing speed. The minimum is located on the curve at point 'd' and is independent of the testing speed.

Stiffness

• Resistance of the metal to changes in length.
• High stiffness corresponds to small deformation in the elastic zone.
• The slope of the straight-line portion of the stress-strain curve represents the modulus of elasticity (E).

Poisson's Ratio

• Ratio of lateral strain to longitudinal strain.
• It's denoted by 'n'.

Resilience

• Energy stored in the metal during loading and recovered after unloading within the elastic region.
• Calculated as the area under the linear portion of the load-elongation curve.
• Resilience = 0.5 * load at proportional limit * elongation at proportional limit

Modulus of Toughness

• Energy absorbed by the material during loading until fracture.
• Calculated as the area under the entire stress-strain curve.

Ductility

• Ability of metal to deform.
• Measured by percent elongation and percent reduction in area. % Elongation= (Lf - Lo) / Lo *100 % Reduction in Area =(Ao-Af)/Ao * 100

###Mechanical Performance Beyond Elastic Region

• Ultimate Tensile Stress: The maximum stress a material can withstand. Calculated as maximum load / initial cross-sectional area.
• Toughness: The energy absorbed by the material up to fracture .Calculated as area under entire stress-strain curve.

يستعرض هذا الفصل كيفية إجراء اختبار الشد الثابت المحوري لعينة معدنية. يحلل العلاقة بين الحمل والانكماش ويقدم معلومات عن المناطق الثلاثة للحمل: المرنة، المرنة-اللدنة، واللدنة. كما يُحسب العديد من الخصائص الميكانيكية للعينة المعدنية المختبرة.