Mechanical Properties Of Polymer Materials

August 22, 2024

Mechanical Properties

1. Tensile strength

In the specified test temperature, humidity and application speed, along the specimen axial direction to apply tensile load, until the specimen damage. Specimen fracture by the maximum tensile stress, called tensile strength (tensile strength). Tensile strength (σt) is calculated according to the following formula:

Where P is the maximum destructive load, N; b is the width of the specimen, m; d is the thickness of the specimen, m. The maximum destructive load of the specimen, N, is the maximum damage load.

1) Elongation at break When the sample breaks, the effective part of the incremental distance between the markers and the initial markers of the ratio of the percentage, known as the elongation at break (elongation). Elongation at break (εt) calculated according to the following formula

Where L0 is the original effective length of the specimen, mm; L is the effective length of the specimen at fracture, mm.

2) Poisson's ratio In the proportional limit of a material, the absolute value of the ratio of the transverse strain caused by a uniformly distributed longitudinal stress to the corresponding longitudinal strain is called Poisson's ratio. Poisson's ratio (ν ) can be calculated by the following formula:

where εt is the transverse strain and ε is the longitudinal strain.

3) Tensile modulus of elasticity In the proportional limit, the ratio of the tensile stress on the material to the corresponding strain is called tensile modulus of elasticity (tensile modulus of elasticity), also known as Young's modulus. The tensile modulus of elasticity (Et ) is calculated according to the following formula:

Where σt is tensile stress and εt is tensile strain.

Test standard: GB/T 1040-2022 Test method for tensile properties of plastics.

2. Compressive strength

Compressive load is applied to both ends of the specimen until the specimen ruptures (brittle materials) or yields (non-brittle materials).

Or yield (non-brittle materials) when the maximum compressive stress, known as compression strength (compression strength). The compression strength (σc) is calculated according to the following formula:

Where P is the breaking or yielding load, N; F is the original cross-sectional area of the specimen, m2.

The compression modulus (Ec) is calculated by the following equation:

Where σc is compression stress, Pa; εc is compression strain.

Test standard: GB/T 1041-2008 Plastic compression performance test method.

3. Flexural strength

The maximum stress produced when a material is subjected to a bending load that destroys or reaches a specified winding degree is called flexural strength. The flexural strength (σf ) is calculated according to the following formula:

Where P is the bending load on the specimen, N; L is the span of the specimen, m; b is the width of the specimen, m; d is the thickness of the specimen, m.

Flexural modulus of elasticity: plastic in the proportional limit of the bending stress and its corresponding strain ratio is called flexural modulus of elasticity (flexural modulus of elasticity), or simply flexural modulus child.

The flexural modulus (Ef ) is calculated by the following formula:

Where σf is the bending stress, Pa; εf is the bending strain.

Test standard: GB/T 9341-2008 Test method for bending performance of plastics.

4. Impact strength

Impact strength (impact strength) represents the maximum ability of the material to withstand the impact load. That is, under the impact load, the material destruction of the work consumed and the ratio of the cross-sectional area of the specimen. There are two test methods for impact strength of materials.

1) Simply supported beam impact test method Unnotched impact strength (αn) and notched impact strength (αk) are calculated according to the following formula:

and

Where, An is the work consumed by the unnotched test, J; Ak is the work consumed by the notched specimen, J; b is the width of the test, m; d is the width of the unnotched specimen, m; dk is the notched specimen notched at the remaining thickness, m. 2) Cantilever beam impact test method The method uses the notched specimen, the impact strength (αk ) is calculated as follows

2) Cantilever beam impact test method This method uses notched specimen, and its impact strength (αk ) is calculated according to the following formula:

Where Ak is the work consumed when the specimen breaks, J; ΔE is the work consumed by throwing the free end of the fractured specimen, J; b is the width of the specimen at the notch, m.

Test standard: GB/T 1043-2018 rigid plastic simply supported beam impact test method

GB/T 1843-2008 Impact test method for plastic cantilever beam; GB/T 14485-1993 Impact test method for engineering plastics

14485-1993 test method for impact resistance of engineering plastics rigid plastic plates and plastic parts; GB/T 11548-1989 test method for impact resistance of rigid plastic plate

Falling hammer method; GB/T 13525-1992 test method for tensile impact resistance of plastics.

5. Hardness

Hardness refers to the resistance of polymer material to indentation and scratch. According to the test method, there are four commonly used values.

1) Brinell hardness HB (brinell hardness)

Put a certain diameter of the steel ball, under the action of the specified load, press the specimen and keep a certain time, to the depth of the indentation on the specimen or the diameter of the indentation to calculate the unit area of the force, with

As a measure of hardness. Their expressions are

and

Where P is the applied load, N; D is the diameter of the steel ball, m; d is the diameter of the indentation, m; h is the depth of the indentation, m.

Test standard: HG2-168-65 Brinell hardness test method for plastics

2) Shore hardness

Under the action of a standard indenter with a specified load, the depth of the indenter's needle pressed into the specimen after a strictly specified period of time is taken as a measure of the Shore hardness value. Shore hardness is divided into Shore A and Shore D. The former is applicable to softer materials; the latter is applicable to harder materials.

Test standard: GB/T 2411-2008 Shore hardness test method for plastics

3) Rockwell hardness

Rockwell hardness has two methods of expression. ① Rockwell hardness scale A certain diameter steel ball, in the load from the initial load gradually increase the main load, and then return to the initial load, the ball in the specimen on the depth of the incremental indentation, as a measure of Rockwell hardness value, expressed in symbol HR. This method of expression is applicable to the harder materials, divided into R, M, L scale.

Test standard: GB / T 9342-88 Rockwell hardness test method for plastics

② Rockwell H hardness to a certain diameter of the steel ball, under the action of the specified load, pressed into the depth of the specimen for the measure of hardness value, expressed in H.

Test standard: GB/T 3398-2008 Indentation Hardness Test Method for Plastic Steel Balls

4) Barcol hardness

A specific indenter is pressed into a standard spring under the pressure of the spring.

Spring pressure with a specific indenter in a standard spring pressure into the specimen, the depth of its indentation to characterize the hardness of the specimen material. This method is suitable for determining the hardness of fiber reinforced plastics and their products, and can also be applied to the hardness of other hard plastics.

Test standard: GB/T 3854-2017 Fiber-reinforced plastics Bachmann (Bakel)

Hardness test method.

6. Creep

Under the condition of constant temperature and humidity, the deformation of the material will increase with time under the continuous action of constant external force.

Under constant temperature and humidity conditions, the material under the continuous action of a constant external force, deformation increases with time; deformation gradually recovered after the removal of the external force, this phenomenon is called creep (creep).

This phenomenon is called creep. Because of the different nature of the external force, often can be divided into tensile creep, compression creep, shear creep and bending creep.

Test standard: GB/T 11546-2022 Determination of creep performance of plastics

7. Fatigue

Fatigue (fatigue) is a material subjected to alternating cyclic stress or strain caused by local structural changes and internal defects in the development process. Fatigue is the process of localized structural changes and development of internal defects caused when a material is subjected to alternating cyclic stresses or strains.

8. Friction and wear

Two objects in contact with each other, there is a relative displacement between each other or relative displacement tendency, the mechanical force between each other to impede the displacement, collectively referred to as friction. The coefficient of friction and wear characterize the frictional properties of materials.

1) Friction coefficient (coefficient of friction)

Maximum static friction Fmax calculated according to the following formula

and

where µk is the coefficient of kinetic friction, and P is the positive pressure, N.

2) Abrasion

The amount of material loss after friction for a certain period of time or course of time under specified test conditions is called abrasion.

The amount of material loss after friction for a certain period of time or course is called abrasion. The better the abrasion resistance of a material, the lower the amount of abrasion.

Test standard: GB/T 3960-2016 Sliding friction wear test method for plastics GB/T 5478-2008 Rolling wear test method for plastics.

Author:

Ms. Tina

E-mail:

sales@honyplastic.com

Phone/WhatsApp:

8618680371609