Helwan University Faculty of Engineering, Mataria Mechanical Design Department Auxetic Polyurethane Foam (Fabrication, Properties and Applications) By Eng.\ HOSSAM IBRAHIM YOUSIF YOUSIF Instructor in the Egyptian Atomic Energy Authority A Thesis submitted to Helwan University In Partial Fulfillment of the Requirements for the Degree of Master of Science in Mechanical Design Engineering Under Supervision of Professor, Dr. Eng. Associate Professor, Dr. Eng. Alaa Mohammed EL-Butch Tarek Hussien EL-Mahdy Vice Dean for students affairs Mechanical Design Department Faculty of Engineering, Mataria Faculty of Engineering, Mataria Helwan University Helwan University Assistant Professor Eng. Khaled Mohammed Zied Mechanical Design Department Faculty of Engineering, Mataria Helwan University Cairo 2012 Helwan University Faculty of Engineering, Mataria Mechanical Design Department Auxetic Polyurethane Foam (Fabrication, Properties and Applications) By HOSSAM IBRAHIM YOUSIF YOUSIF Instructor in the Egyptian Atomic Energy Authority A Thesis Submitted to Helwan University In Partial Fulfillment of the Requirements for the Degree of Master of Science in Mechanical Design Engineering Approved by the Examining Committee: Prof. Dr. Eng.\ Ramadan Ibrahim El-Seoudy ( ) Professor in Mechanical Design Department-Faculty of Engineering -Suez Canal University Prof. Dr. Eng.\ Younes Khalil Younes ( ) Professor in Mechanical Design Department-Faculty of Engineering, Mataria-Helwan University Prof. Dr. Eng.\ Alaa Mohammed EL-Butch ( Thesis Advisor ) Professor in Mechanical Design Department-Faculty of Engineering, Mataria-Helwan University ( ) Assoc. Dr. Eng.\ Tarek Hussien EL-Mahdy ( Thesis Advisor ) Assoc. Prof. in Mechanical Design Department-Faculty of Engineering, Mataria-Helwan University ( ) Cairo 2012 Abstract Modern technology requires new materials of special properties. For the last two decades there has been a great interest in a class of materials known as auxetic materials. An auxetic material is a material that has a negative Poisson's ratio which means that this material expands laterally when they subjected to a tensile force unlike most of the other traditional materials. This material has superior properties over the traditional material such as high shear modulus and high impact resistance, which makes this material a good candidate for many engineering applications. In the present research work, auxetic flexible polyurethane polymeric foams having different densities were fabricated from conventional flexible polyurethane polymeric foam at different compression ratios. The microstructure of conventional and processed foams was examined by optical microscope to compare between the two structures. The microstructure of processed foam was compared with the one presented in the literature and it has shown the auxetic structure configuration. This is the first time to produce auxetic foam in Egypt. Conventional and auxetic foam samples having cylindrical and square cross-sections were produced from foams having different densities (25 kg/m3 and 30 kg/m3). The compression ratios used to produce the auxetic samples are (5.56, 6.94 and 9.26). Four mechanical tests were carried out to get the mechanical properties for both conventional and auxetic foams. Two quasi-static mechanical tests "tension and compression" and two dynamic mechanical tests "Hysteresis and resilience" were carried out to compare between the conventional and auxetic foams. The quasi-static tensile test was carried out at speed was adjusted to be position control rate of 0.2 mm/s. The compression and hysteresis tests were carried out at strain control rate of 0.3 S -1. The data recorded from the machine were stress and strain. The modulus of elasticity and Poisson’s ratio of the test samples were obtained from tensile and compression tests. Poisson’s ratio of the test samples was measured using video measurements using a dedicated Matlab and Get Data Graph Digitizer programs. Generally, the auxetic behaviour was observed for most of the processed foam. It has been observed for all compression ratios and the yellow and the grey foam only. The obtained values of Poisson’s ratios was between -0.27 and 0.74. The value of the modulus of elasticity for auxetic foam was lower than the conventional foam. For example the grey auxetic foam (B) with a compression ratio of 50% has a modulus of elasticity of 30.02 kPa which is lower than the conventional foam sample (A) by 77.3 %. i The energy absorbed of the foam was calculated using the compression and tensile test results. It has been observed that auxetic foam has higher absorbed energy than the conventional foam. For example for grey PU foam sample has a compression ratio of 5.56 and a density of 109.6 kg/m 3, the energy absorbed was 3.98 kJ/m 3, which is higher than the conventional PU foam sample by 69.6%. In the resilience test the value of resilience of the auxetic grey foam was higher than the conventional foam. For example for grey foam has a compression ratio of 9.26 and a density of 125.5 kg/m3, the resilience percentage was 38% which is higher than the conventional foam by 7.7%. The produced auxetic polymeric foam material has a potential to be used in the following areas: • Biomedical field as dilator and artificial blood vessels [16]. • Car body parts (head rest and seats) and nose-cone of aircrafts [33,34]. • Body armour [35]. • Can be used in the packing of electronic equipment. • Can be used in the pumps and Heat Exchangers fastenings as vibration absorbers. • Can be used in the packing and seals of valves and pumps. ii Table of Contents Abstract ................................................................................................................................ .......i Table of Contents ................................................................................................ ........................iii Acknowledgments ................................................................................................ .......................v Nomenclature ................................................................................................ ..............................vi List of Figures ................................................................................................ .............................viii List of Tables ................................................................................................ ...............................xiv CHAPTER (1) INTRODUCTION AND LITERATURE SURVEY 1.1 Introduction ..................................................................................................................... 1 1.2 Literature survey ............................................................................................................. 2 1.2.1 Negative poisson's ratio.............................................................................................. 2 1.2.2 Auxetic materials........................................................................................................ 4 1.2.3 Flexible polyurethane (FPU) polymeric foams .......................................................... 5 1.2.4 Conventional flexible polyurethane (FPU) foam applications ................................... 6 1.2.5 Previous work ............................................................................................................. 7 1.3 The Objective of the research ...................................................................................... 10 CHAPTER (2) POLYURETHANE FOAM SAMPLES FABRICATION AND PREPARATION 2.1 Fabrication method of flexible Polyurethane foams .................................................. 11 2.2 Manufacturing technique of auxetic PU polymeric foam .......................................... 12 2.3 Adaptation dimensions of samples for testing ............................................................16 2.4 Samples label .................................................................................................................17 CHAPTER (3) POLYURETHANE FOAM TESTING AND MEASURING TECHNIQUES 3.1 Testing techniques ......................................................................................................... 19 3.1.1 Compression ratio measurement...............................................................................19 3.1.2 Density measurement................................................................................................ 19 3.1.3 Poisson’s ratio measurement .................................................................................... 20 3.2 Mechanical testing machines ........................................................................................ 21 3.2.1 Zwick universal testing machine ..............................................................................21 3.2.2 Zwick rebound resilience tester machine .................................................................22 3.3 Mechanical testing and methodology .......................................................................... 24 3.3.1 Tensile test and methodology................................................................................... 24 3.3.2 Compression test and methodology..........................................................................27 3.3.3 Hysteresis test and methodology ..............................................................................30 3.3.4 Resilience test and methodology ..............................................................................31 CHAPTER