Chapter 5 Hardness Test PST472 PDF

PST472 POLYMER PHYSICAL TESTING & ANALYSIS HARDNESS TEST 2 LESSON OUTCOMES Upon the completion of this Define the term Explain the chapter, the hardness and significance of students should be apparent hardness. hardness testing. able to:...

PST472 POLYMER PHYSICAL TESTING & ANALYSIS HARDNESS TEST 2 LESSON OUTCOMES Upon the completion of this Define the term Explain the chapter, the hardness and significance of students should be apparent hardness. hardness testing. able to: Describe the basic Explain the factors principle of State and explain influencing the hardness testing the types of hardness value. and the types of hardness testing. indenter used. Describe the test State and describe Describe the procedures of the types of working principle of Durometer hardness tester. Rockwell hardness. hardness tester.  3 INTRODUCTION  A very desirable objective of hardness test is for the rapid assessment of the stiffness or rigidity of materials.  Hardness test is important for quality control of material.  Hardness test normally involve the quantitative assessment of the resistance to penetration (indentation) of a material by an indenter (impresser).  The indenter can have a variety of shapes such as sphere, pyramid, cone, etc.  4 TYPES OF INDENTORS i) Diamond Indenter: ii) Ball Indenter:  5 INTRODUCTION This test is quick and considered to be nondestructive test when the marks or indentations produced by the test are in low stress areas. Due to this advantage, hardness test is widely used. The real purpose of hardness test is to determine the elastic modulus of the material under conditions of small strain.  For polymeric materials, the interpretation of results in terms of conventional mechanical characteristics is generally difficult and complex. This is due to the combination of elastic and plastic non-homogeneous 6 INTRODUCTI deformations and the time dependence ON of the mechanical properties. The hardness relationship to mechanical properties is usually not straight- forward, but there is a tendency for high modulus & strength to correlate with higher degree of hardness within classes of materials.  The results of different tests are also often difficult to compare, and the relationships or correlations between scales, which appear in publications, are only very approximate. The various tests, however, can be very valuable, particularly for comparing generally similar materials. 7 INTRODUCTIO N Hardness measurements basically involve the surface of test specimens. Since it is established that many polymeric materials and processing techniques lead to structural in- homogeneities, particularly near the surface of parts, results should be interpreted in the appropriate context.  INTRODUCTION 8  DEFINITION: Hardness is the resistance of a material to deformation, particularly permanent deformation, indentation or scratching  For elastomers and some polymers, hardness is defined as the resistance to elastic deformation on the surface.  INTRODUCTION  Various standards testing method for hardness are:  IS0 48, IS0 1400, IS0 7619, IS0 1818  ASTM D 2240, ASTM D 1415 9  BS 903: Part A26, BS 903: Part A57  DIN 53519-1  Hardness for plastics: ASTM D785  Hardness unit: IRHD (International Rubber Hardness Degree)  To indicate the degree of cure in thermosetting resin moulding and rubber vulcanization To verify the heat 10 The treatment of a part most common uses for To determine if a hardnes material has the properties necesarry s tests: for its intended use. Temperature and Humidity Higher temperature and higher humidity caused lower hardness value. Surface conditions A smooth molded surface 11 The has a higher value than a factors influencin machined one. g Filler hardness value: Addition of filler will increase the hardness value.  Hardness is the resistance of material to indentation and it is determined by measuring the permanent depth or width of a test indentation. When using a fixed force (load), and a given indenter, the smaller the indentation, the 12 BASIC harder the material (high hardness value) PRINCIP LE The depth of indentation is depands on the following factors: the the elastic the time/duration dimensions/shap load applied modulus of the of measurement e of the indenter material  The term standard hardness refers to measurements made on standard test pieces.  Apparent hardness is a macro- hardness (hardness testing in the macro scale). APPAREN  It normally involves the measurement on non-standard test T piece. HARDNES  Generally the apparent hardness will increase as the test piece thickness is reduced because of S the effect of compression against the rigid test piece support. 13  Macro hardness test is applied to test a larger test load (1kg or more). Apparent hardness is macro hardness Micro hardness test is applied to test with low applied loads (1-1000gf). Test is applicable when hardness of coatings, 14 Differences surface hardness or hardness of different phase in the multiphase material is measured Nano hardness test measure hardness by indenting using very small(1nano newton)  15 TYPES Durometer / For Flexible PVC, thermoplastics Indentation elastomers and PE (ASTM D2240) Hardnes Barcol Wallace (ASTM s tester D2583) For reinforced and non reinforced rigid plastics For relatively hard Rockwell plastics such as acetals, nylons, (ASTM 785) acrylics and PS.  INTRODUCTIO N  Typical Hardness Values of Some Common Plastic Materials: 16   The Rockwell Hardness test is a hardness measurement based on the net increase in depth of impression as a load is applied.  Used for harder plastic such as nylon, ROCKWE polycarbonate, PS.  LL Hardness numbers have no units and are commonly given in the R, L, M, E and K scales. 1 7 HARDNE  The hardness scale in order of increasing SS hardness are R, L, M, E and K scales. TESTER  The higher the number in each of the scales, the harder the material.  The diameter of the ball indenter decreases as one goes from R to K.  ROCKWELL HARDNESS 18 TESTER  The working principle of Rockwell hardness testing machine is shown below: 1. The indenter moves down into position on the part surface. 2. A minor load is applied and a zero reference position is established. 3. The major load is applied for a specified time period (dwell time) beyond 0. 4. The major load is released leaving the minor load applied. Specimen size: A standard specimen of 6.4mm (0.25 in) thickness is either molded or cut from a sheet. 19  INTERNATION  The international rubber hardness 2 0 AL RUBBER (ASTM D1415) bears some similarity HARDNESS with the Rockwell hardness method.  The standard test uses a spherical indenter (ball) of diameter, d ≈ 2.5 mm.  The ball penetration is related to international rubber hardness degrees (IRHD), which correspond approximately to Shore A values.  DUROMETER HARDNESS TESTER  It is used for measuring the relative hardness of soft material.(for rubber and commonly for softer plastic such as vinyls, polyolefins, fluoropolymers.  The hardness determination is based on the 21 penetration of a specified indenter forced into the material under specified conditions.  The tester consist of pressure foot, a spring loaded indentor and an indicating device.  A total of 12 Shore durometer hardness scales have been developed over the years, but only two are widely used today. DUROMETER HARDNESS 22 TESTER Used for non-rigid to semi-rigid plastics, rubbers and elastomers of Shore A a minimum thickness of 6 mm (ISO 868) – medium materials. Used always for plastics showing Shore D higher hardness – harder materials.  The difference is in the shape and dimension of the indenter.  Shore 00: For soft materials – This scale is used when measuring soft materials like, foams, silicone rubbers, gels, latex and similar. 23 DUROMETER HARDNESS TESTER DUROMETER HARDNESS 24 TESTER  Shore D:  Shore A: Used an indenter with a truncated cone point.  The pressure foot is The test is carried out pressed into the by first placing a specimen making it specimen on hard flat parallel to the surface surface. of the specimen. 25 DUROMET ER The durometer Repeat and make 5 HARDNES determinations of hardness is read within hardness at different S TESTER 1 sec after the pressure foot is firm contact with positions at the specimen and calculate TEST specimen. the mean or median. PROCEDU RE DUROMET ER HARDNES S TESTER 2 6  Disadvantage of Durometer Hardness Tester:  The indenter is easily damage and it gets out of calibration easily  It is also difficult to recalibrate, & there is no absolute standard to which it may be compared. The hardness of the rubber is 27 measured by using a Shore A hardness tester.  Specimen Size: 2 DUROMET  The test specimens are generally 6.4mm 8 (¼ in) thick. ER  It is possible to pile several specimens to HARDNES achieve the 6.4mm thickness, but one S TESTER specimen is preferable. Data:  The hardness numbers are derived from a scale.  Shore A and Shore D hardness scales are common; with the A scale being used for softer and the D scale being used for harder materials.  POCKET DUROMETER HARDNESS TESTER  An extremely convenient and widely used measuring device, that can be carried anywhere.  The principle of operation of this instrument can 29 be linked to pressing a ball point pen into the material to be tested and relating the depth of penetration of the point to an agreed scale of numbers.  A deeper indentation indicates a softer material, and a lower durometer number.  POCKET DUROMETER HARDNESS TESTER  Advantage:  light weight and small size, the user can always carry the QC. QC Pocket Shore Durometer/Hardness 30 Tester (available in A & D Scale)  WALLACE HARDNESS 31 METER Itsindenter is a spherical point, which is less easily damaged than the Shore indenter. Itscalibration can be checked with a dead weight provided with the instruments, and adjustments can be made without taking the instrument apart. Its scale is like Shore scale. BARCOL HARDNESS 32 METER  Standard: ASTM D2583  For measuring hardness of reinforced rigid plastics.  The tester is a portable instrument that can be carried around to measure fabricated parts and test specimen.  Thickness of the test specimen must be at least 1.5 mm or 1/16 inch.  It uses an indenter like that used in the Sore D method, except for a flat tip instead of a rounded one.  The hardness value of the material is indicated as, for example: Barcol 60B. THANK YOU