LEEA Foundation Certificate (Global) Course Workbook PDF

LEEA – Foundation Certificate (Global) – Course Workbook The Tensile Test The tensile test, also known as the tension test, is probably the most fundamental type of mechanical test you can perform on material. ▪ The Tensile Test This tensile test reveals a great amount of information about...

LEEA – Foundation Certificate (Global) – Course Workbook The Tensile Test The tensile test, also known as the tension test, is probably the most fundamental type of mechanical test you can perform on material. ▪ The Tensile Test This tensile test reveals a great amount of information about the material and quantifies the important properties of the material. ▪ Why is this test important? Lifting equipment examiners need to know these properties and how they are determined in order to understand various material specifications and relate these to their suitability for making lifting equipment. A standard size specimen of the material to be tested is machined to a predetermined size. The cross-section of the specimen is usually round, square or rectangular. For metals, a piece of sufficient thickness can be obtained so that it can be easily machined - a round specimen is commonly used. For sheet and plate stock, a flat specimen is usually used. From the tensile test, we can use the results to determine how a material will react under tensile loading. Typical properties revealed include the elastic limit, yield point, ultimate tensile strength and elongation/reduction in the cross-sectional area of the material under test. A tensile load is applied to the specimen until it fractures. During the test, the load required to make a certain elongation on the material is recorded. A load/elongation curve is plotted by a recorder so that the tensile behaviour of the material can be obtained. 41 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook From a tensile test, a stress/strain, or sometimes known as a load/extension curve can be produced. Five definite points can be seen as the line of the graph: A. Limit of Proportionality B. Elastic Limit C. Yield Point D. Tensile Strength E. Ultimate Breaking Stress Question: What is meant by the term, ‘local necking’? (Select one answer) □ a. When a material under tensile load exceeds its maximum tensile strength, a reduction in material cross-sectional occurs which is known as local necking. □ b. When a material reaches its elastic limit, the measured reduction in cross-sectional area is called the local necking yield. Notes: 42 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Tensile Test Definitions: There are some key phrases/terms used regarding tensile test – see below: Limit of Initially as the force is applied the stress and strain are proportional Proportionality until point A is reached. This is the point at which the graph is no longer a straight line. This point is known as the Limit of Proportionality. The Elastic Limit This is the point up to which the material remains elastic. Within the elastic limit, the test piece will return to its original dimensions if the load is removed. (With mild steel this point practically corresponds with the Limit of Proportionality. This is not generally true of other materials or for materials that have been overstrained). When this point has been exceeded the extension is permanent and is referred to as Plastic Deformation. Yield Point Slightly above the elastic limit, the Yield Point is reached when a sudden permanent extension, B to C, occurs without any increase in load. (Sometimes there is a slight drop in the load, due to the extension, giving an upper and lower yield point). Tensile Strength The Tensile Strength is reached at this point. When this is passed the cross-sectional area becomes noticeably smaller and ‘necking’ occurs. This is the point of maximum load. Ultimate Breaking This is the actual breaking load where an increase in stress is obtained Stress with a reduction in load. Although the value is smaller than the tensile strength this gives a false impression of what occurred. From points D to E the section of the test piece considerably reduces as it ‘necks’ - thereby effectively increasing the stress. However, as the graph records the stress as load over the original cross-sectional area, it appears to decrease. There is a clear difference between a ductile material and a brittle material under the same tensile test. A brittle test piece withstands deformation until the stress applied is at a relatively high level. It then yields, deforms and fractures. A ductile test piece withstands deformation but yields at a lower level of stress than the brittle test piece. This is because the ductile material is not as strong as the brittle material. The ductile material then continues to elongate, reaching its maximum tensile stress and eventually fracturing. 43 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Shear, Tension and Compression Loading conditions: lifting equipment may be subjected to single or multiple types of stress: Single shear – forces acting across a material o Example: A lifting lug on a waste skip being lifted Double shear – forces acting across a material in two areas o Example: A shackle pin under load Compression – a pushing force o Example: A jack body under load Tension – a pulling force o Example: A chain sling under load 44 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Torsion – a twisting force o Example: A rotating gearbox shaft driving a hoisting appliance Notes: 45 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Units of Measure A unit of measure can be described as a standardised quantity of a physical property, used to determine multiple quantities of a given property. For example: Weight Length Mass Force Different systems of units are based on different choices of a set of fundamental units. The most widely used system of units is the International System of Units, or ‘SI’. There are seven SI base units. All other SI units can be derived from these base units. Under the SI system when marking lifting equipment only one decimal point is used for fractions of a tonne e.g. 2.1t, apart from when marking 0.25 which is always to two decimal places, e.g. 2.1t, 2.2t, 2.25t, 2.3t, 2.4t, 2.5t, 2.6t, 2.7t, 2.8t, 2.9t Notes: 46 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Question: Let's check your understanding of symbols relating to units of measure. From the list below, select which one you think matches the symbol of 'cwt'. (Select one answer) □ Pound □ Hundredweight □ Imperial or US Ton □ Metric tonne □ Kilograms NOTE: Question: From the list below, select which one you think matches the symbol of ‘T’. (Select one answer) □ Imperial or US Ton □ Hundredweight □ Kilograms □ Metric tonne □ Pound NOTE: Symbols and Conversions Ton (US) T = Imperial or US Ton 1 Ton (US) = 2000lbs = 907.185kg = 0.907t (metric) (commonly referred to as the ‘short Ton’) 1 tonne (Metric) t = Metric tonne 1 tonne (metric) = 1000kg = 2204.62lbs (rounded to 2204lbs) 1 Ton (Imperial) kg = Kilogrammes 1 Ton (imperial) = 1016kg = 2239.9lbs (rounded to 2240lbs) (‘long Ton’ in the USA) 1 cwt cwt = Hundredweight 1 cwt = 50kg The hundredweight was established in the imperial measurement system in which 1 Ton is divided into 20 subdivisions, each being a hundredweight. Occasionally, lifting accessories may be found in service today with a marked safe working load or working load limit of ‘cwt’. 1 hundredweight (cwt) = 50 kg, therefore, a marked load limit of 2 Ton 1 cwt = 2050kg, rounded down to 2t. 47 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook ▪ 1kg = 2.2lbs ▪ 1 inch = 25.4mm ▪ 1 foot = 12 inches ▪ The SWL of new equipment will normally be in the metric units of tonnes (t) or kilograms (kg) or imperial units of Tons (T) and Pounds (lb). The generally accepted rule is that a SWL of less than one tonne or Ton are marked in kilograms or pounds, respectively. Notes: 48 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Types of Verification New equipment should comply with the essential health and safety requirements stipulated in any applicable legislation, product standard where available, and issued with the required conformity documentation. This documentation is often combined with the results of the verification and together they form the ‘birth certificate’ which is an important legal document. New Equipment For new equipment, the verification methods used by the manufacturer will depend on the standard being worked to. Some equipment is unsuitable for proof load testing due to the nature of the materials used, e.g., textile slings. Some items are assembled from components verifiedto their own standards so no further tests are required, e.g., grade 8 mechanically assembled chain slings. Once in service, the verification methods used will be those deemed necessary by the Competent Person in reaching their conclusions about fitness for purpose. Types of Verification There are many types of verification and test available to the examiner, including: 49 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024  LEEA – Foundation Certificate (Global) – Course Workbook Test Machines and Force/Load Measuring Equipment Many of the product standards and codes of practice that require the application of a load, or force, lay down the accuracy to which the test load or force must comply. For example, BS EN 818-1 for chain requires accuracy of ±1%. It requires that test machines and load cells be calibrated and verified by a competent person or authority, in accordance with ISO 7500-1 at intervals not exceeding 12 months. It also requires that the accuracy of the applied load/force must be within that required by the standard being worked to and, in all cases, within ±2% of the nominal load/force. ▪ ▪ 1.0 ▪ Grade 0.5 = ±0.5%, 1.0 = ±1% and 2.0 = ±2%. The certificate will also give the Lower Limit of Calibration. This will be expressed as a load or force, depending on the units in which the machine or device is calibrated. This is the minimum load/force that can be read from the display within the required accuracy. Test loads below this cannot be measured with this equipment. In some cases, there may also be a similar restriction on the upper limit. 50 Page © LEEA Academy - FOU (Global) Workbook v 1.6 Jan 2024