Tensile Properties of Engineering Polymers - Research Proposal Example

PORTFOLIO By Student’s name Course code and name Professor’s name University name City, State Date of submission Table of Contents Table of Contents 2 Experiment 1 3 Introduction and background 3 Methodology 4 Results 5 Discussion 7 Conclusion 8 Experiment 9: Tensile Properties of Engineering Polymers 9 Introduction and background 9 Apparatus 10 Methodology 11 Results 12 Discussion 13 Conclusion 15 Part 3 - Building Components and types 16 Fire Protection Standards for Design and Construction 16 Part 4: Failure Modes 19 Behaviour of Materials in Fire Conditions 19 Failure Modes 21 Signs and Hazards of Collapse in Construction 23 List of References 25 Experiment 1 Introduction and background The presence of various kinds of cables in construction pose fire risks of different magnitudes depending on materials used to manufacture them. The hidden danger that these cables possess is associated with the rates of fire spread during time of catastrophes since the materials utilised for insulation purposes is highly flammable. Therefore the materials to be used in cable manufacturing must be tested and approved by relevant authorities. Building designers must ensure that the materials being used in a building are approved by these authorities. The advancement in material science has seen the manufacture of fire retardant cables which are used along routes believed to be risky in order to reduce the probability of electric fires. More recently fire retardant cables have gained popularity among construction contractors for survival of buildings. This experiment seeks to study the flame propagation characteristics of single wire. This test is carried out on a 100cm cable sample fixed at an angle of 45º and 125mm flame long at its bottom. Once the burning is completed, the specimen is deemed to have passed the test only if the charred position does not affect the lower edge of the top clamp – equivalent to 420mm above the point of flame application. Methodology The availability of the cables under test was checked to ensure that all the three samples with two pieces for each type was available. The samples were marked at 100mm intervals in readiness for experiment commencement. 1m cable was clamped tightly at the top and bottom of the test apparatus and 20mm line marked at the top and bottom of the sample leaving the burning distance with exactly 420mm. The Bunsen burner was set on a flame approximately 125mm high while ensuring it possessed an inner blue cone to avoid excessive smoke from fuel. The filter paper was placed underneath the experimentation cable. The thermocouples were set in a manner that ensured they touched the top and bottom of the wire and then the data logger put on. The flame was impinged on 20mm line though at an angle. The flame was let to impinge on the cable for 60 seconds and then removed. The thermocouple temperatures were checked for both edges after every 15 seconds and recorded for analysis purposes. The cable was observed as burning at the top of the clamp and the droplets from the cable igniting the filter paper took place. This procedure was repeated for the rest of the samples that were availed for experimental purposes. Figure 1: Test setup. Results The experimental results were recorded and tabulated as shown in tables 1 and 2 below. Table 1: Sample measurements. Measurements Length of Flame Propagation Filter Paper Observations Temperature Readings Every 15 Seconds Sample 1 (Kettle Lead) 52 No Observations See table 2 Sample 2 (Kettle Lead) 55 No Observations See table 2 Sample 3 (Twin + Earth) 35 No Observations See table 2 Sample 4 (Twin + Earth) 40 No Observations See table 2 Sample 4 (Narrow) 83 Minor Carbon Spots See table 2 Sample 6 (Narrow) 83 Minor Carbon Spots See table 2 Table 2: Average temperature Readings Every 15 Seconds Time (s) Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 0 21.5 22.75 23.75 22.25 21 21 15 21.5 22.25 23.25 21.5 21 22 30 21.75 22.75 24.75 22.25 21 22.5 45 22.5 22.75 26.0 22.75 21 24.5 60 22.75 22.75 27.0 22.75 21 27.5 75 23.5 24 29.25 22.25 _ 30 90 24.75 24.25 _ 22.25 _ 31.5 Figure 2: A graph of temperature against time. Discussion The factors that influence the fire behavior of cables include the chemical composition of the insulating materials, availability of combustible gases in the compartment, the amount of current passing through the cable (depends on load), the cross sectional area of the cable, location of the said cable (middle or outermost of the bundle) and the availability of aggravating material or fuel around it such as compartment materials. In order to minimize electrical fires, construction designers must ensure that they follow rules and guidelines governing the industry. Isolating the cables to areas where fire is unlikely to occur or even areas where combustible materials is absent. The inclusion of fire blankets or fire retardant materials pose as important measures towards avoiding probability of fire occurrence. The cables should be well rated in order to avoid fire eruption due to overload. For purposes of extinguishing electrical fires also classified as Class E fires, dry powder and carbon dioxide are the only deployable fire extinguishers due to the risks of being electrocuted in case of liquid or foam usage. Electrical fire is considered as dangerous fire unless the source of electricity is unplugged. Using liquid or foam extinguishers may render the circuit complete and end up electrocuting the person extinguishing it. Further the organic material used as insulation poses as a danger because of the chemical makeup which may hurt the respiratory system of the fire fighter. Conclusion Electrical cables insulation pose a lot of negative factors when it comes to fire catastrophes. In an experiment setup to investigate rate of combustion in electrical cables, it was established that the rate of fire spread is very high when the cable being used contains readily combustible material. The low diameter material (1.5mm) achieved a high rate of burning as compared to 3-core 1mm squared cable because of its high susceptibility to fire. In the discussion section, it was established that electrical fires pose dangers of electrocution to fire fighters thus liquid or foam extinguishers should not be utilised. Experiment 9: Tensile Properties of Engineering Polymers Introduction and background Polymers or plastics are formed out of long chains of carbon compounds that bestow special properties depending on the present elements. Polymers are characterised by their light weight, resistance to corrosion, recyclability and ease of fabrication. Engineering plastics possess physical properties that enable them to perform exceptionally in structural setup even under extreme conditions such as exposure to temperatures, chemicals, loads and physical environments. Comparing polymers to metals in terms of applications it has been established that the clarity, self-lubrication and ease of decoration are now becoming the overriding objectives in its usability. Plastics do not conduct electricity and heat – factors that make it applicable for insulation in a diversity of industries. The fact that plastic is flexible has furthered its use as an electrical insulator for high voltage units and lines. Plastic properties can also be modified through chemical manipulation, reinforcement and fillers depending on the targeted achievements. Plastics have been utilised in wide areas of engineering such as high stress units, heat and chemical resistant units, low friction components, high light transmission applications, housings, electrical parts and other building construction functions (Foy, 1969). In order to establish the mechanical properties of plastic material prior to usage, there are various methods that have been developed. Tensile tests for example have been utilised since time immemorial to determine various basic properties of design materials. The most common obtainable property through the tensile test is the tensile yield strength which is the maximum engineering stress normally denoted as N/mm2. The yield point, where the plastic sample begins to neck down can also be determined through careful observation or use of advanced or computerised tensometers. The ultimate yield strength denoted as N/mm2 can also be determined by finding out the highest possible stress in a material. The elongation index of a material is determined in terms of percentage change in length per unit length when the material is exposed to a certain amount of load. The tensile modulus can also be determined by finding the ratio of stress against strain – this is carried out on points indicating elasticity. The tensile properties that are obtainable through this kind of mechanical analysis of structural components can be utilised in development of new materials or establishing the applicability of a given material. Material strength comes in as a primary concern in most designs and therefore, finding a way of measuring this factor offers extended convenience to engineers. This experiment utilises the tensile test in ascertaining the ductility and strength of plastic engineering materials. In such a scenario, the test piece is held by a suitable device (tensometer) and subjected to uniaxial load until it completely fails. Apparatus The apparatus required for the success of this experiment was the W-series tensile testing machine. The samples that were used included 2 white nylon bars (white), 1 low density polyethylene (yellow) and polycarbonate (green). The sample was machined to achieve the shape shown in figure 1 below. Figure 1: Test specimen. Methodology The overall length of each sample was taken and recorded in the result section. The gauge width was then measured and recorded in mm as shown in the table 1 in the results section below. The gauge thickness was also measured and recorded together with the other principle dimensions above. The first test sample was placed on the machine grips and tightly held for commencement of the experiment. The tensile test machine was setup to test plastic material in its operation menu at a strain rate of 5mm/min. Once the sample was confirmed to be in place, the test machine was zeroed in readiness for test commencement. The machine was then activated to start the experiment and once the peak load was achieved, the value was recorded. The machine was then set to continue with the experiment until the sample was stretched to breaking point and the results printed. The sample was then removed from the machine and the new overall length measured. The thickness and width of the sample at the broken edge were also measured and recorded in table 1 below. The test data was exported to the computer in Microsoft Excel format and graph plotted for analysis. The machine was then reset and the experiment carried out for the remaining samples. Results SAMPLE LOW DENSITY POLYSTYRENE POLYCARBONATE NYLON NYLON Strain Rate 5mm/min 5mm/min 5mm/min 50mm/min Colour Code Blue Green White White Original Overall Length (mm) 115 115 115 115 Original Thickness (mm) 4.1 4.1 4.13 4.13 Original Width (mm) 10.24 10.24 10.24 10.24 Original Cross-sectional Area (mm2) 13.2 13.2 13.39 13.39 Length after Test (mm) 152 192 310 176 Width after Test (mm) 6.1 7.87 6.44 5.96 Thickness after Test (mm) 2.55 2.9 2.1 2.15 Cross-sectional Area after Test (mm2) 5.11 6.61 3.46 3.63 Reduction in Area (%) 61.3 49.9 74.2 72.9 Elongation (%) 32.2 67 170 53 Peak Load (N) Yield Stress (N/mm2) Fracture Stress (N/mm2) Ultimate Tensile Strength (N/mm2) Table 1: Experimental results Figure 2: Typical graph of stress-strain for plastic samples. Discussion The percentage elongation for the samples was calculated and recorder in table 1 above. It was established that nylon had the largest elongation index at 170% while polystyrene was the lowest with 32.2%. It was also observed that under gradual loading (5mm/min), nylon was able to perform better mechanically. On the other side, nylon performed poorly under abrupt loading 50mm/min thereby lowering the elongation index to 53%. This translates to a ductility variation through various modes of loading. Nylon also exhibited the highest % in cross-sectional area reduction (74.2 and 72.9 for 5mm/min and 50mm/min respectively) due to its high elasticity as compared to its counterparts namely polycarbonate and polystyrene. Thermosets are plastics which achieve permanent mechanical properties i.e. rigidity when cured. On the other side thermoplastics are organic materials that achieve reversible properties. These materials can be melted for process for mouldability into other forms and shapes when cooled to their final phases. These materials are differentiated from their performance and their adaptability to the market requirements. While the basic commodity materials available include polypropylene, polyvinyl carbon, polystyrene and polyethylene, the materials largely applied for the engineering applications include various types of nylon, polycarbonate and polyesters (Scotts Tool, 2007). As shown in figure 2 above, the elastic section starts right from the origin to point A. This portion is characterised by direct proportionality between stress and strain as per Hooke’s law. The proportionality limit is however exceeded beyond point A where the material now reaches the yielding point after which it enters the plastic zone. A material can still regain its initial properties when still under the elastic region but once it exceeds it cannot. Between point C and D the material exhibits plasticity a point during which the material decrease the cross sectional area without any indicators of going back to normal (Total Materials, 2010). The liquid glass transition temperature is also be used to indicate the temperature resistance property of plastic. During glass transition stage, the reversibility in properties still holds for amorphous materials. Conclusion This experiment was successful in establishing the mechanical properties of plastic materials. Tensile tests can be used for establishing such properties as strain and stress in order to come up with other basic properties such as ductility an elasticity of a material. It was established that nylon which is a thermoplastic has better elastic properties than polycarbonate and polystyrene. This also proves that nylon possesses better formability than the other samples being in possession of better elasticity. It is recommended that nylon be exposed to low loads in order to achieve better performance. Part 3 - Building Components and types Fire Protection Standards for Design and Construction Design and construction of buildings for fire protection requires keenness in every intermittent phase so as to eliminate or at least lower the effects of fire. Prior to construction, designers are required to consult with fire engineering experts in order to achieve the best results. Prior to the design stage, communication among stakeholders is an important parameter towards an architectural layout that is likely to be workable solution against fire occurrences. This is because the requirements are understood prior to commencement of a construction project. Fire engineers are required to consult with the client whose construction is under design preparations to come up with simulations and analysis for final occupancy as per the requirements. The designers must also maintain an alliance with the code authorities when it comes to new or unclear legislations so as to avoid designs that cannot be insured against risks of fire. Furthermore, approval of the designs is usually carried out by the local authorities on construction. Therefore, it is important to create an understanding on the authority’s interpretation of a given building design or blue print (Chibbaro, 2009). Today, fire protection engineers form a very vital combination for construction design teams. Their role is imperative to ensuring that the systems, materials and fire protection features are well incorporated into the designs. Ensuring that contingency measures are put in place as early as the design phase secures the construction workers’ confidence on working environment safety. The fire engineers should oversee the design so as to lead the architectures on where hazardous materials should be stored during the construction stage so as not to endanger human inhabitants. Locating of the fire fighting equipment such as pumps, hoses and control panels is mandated to the fire engineers in conjunction with owners so as to avoid conflict of interests. With the help of fire engineers, the building permits can be obtained through design adherence to existing codes (Chibbaro, 2009). During the construction phase, the project managers should ensure that they have fire protection devices. Induction and equipment usage lessons should be administered to construction workers by fire engineers in case an emergency response due to fire may be required at one time. Guidelines with regard to material storage and disposal should be offered as soon as work commences in order to avoid wild fire hazards from affecting the project. Fire engineering experts have proven efficient on most work sites to an extent of reducing the dangers of fire by considerable margins. Provision of fire escape to site and temporary buildings must be provided by the fire engineers (Chibbaro, 2009). During the erection phase, the workforce should be alerted on safe fire practices and escape routes. The temporary enclosures should be constructed using non-combustible materials or any other fire retardant. In case where high-rise buildings are being constructed, at least one stair case must be availed prior to completion and fire extinguishers be furnished in every room of the building just in case fire erupts. The fire protection engineer is required to determine all the project requirements as per the code of the authorities and also give the specifics of emergency responders and the construction documents. Elevators and hoist lie in the hands of the fire engineers as they are the ones who should dictate the safety of the construction with regard to fire. Codes offer clear guidance to the project team as a way of self protection and safety (Chibbaro, 2009). During the interior work, the fire protection systems are installed and a fire engineer must be involved in acceptance testing of the outcome of the design and the two areas of concern include removal of provisional appliance covers and impairment of the notification system. Concealed areas should then be inspected to see that the safe materials checklist is fulfilled. Ensuring cooperation between the project team and the fire engineer gives good returns when it comes to certification. The building at this stage is also checked for phasing in order to establish whether the egress principles were adhered to. Emergency response agencies are then invited in conjunction with the fire engineer in order to carry out a system check for the fire detection and control system just before the handover stage. The habitants are also given education on the installed systems prior to occupancy (Chibbaro, 2009). Part 4: Failure Modes Behaviour of Materials in Fire Conditions Describing material properties in common materials is done using basic theoretical approaches such as ignition, flame spread and the burning rate. Material properties that should hence be discussed in such analysis include heat of combustion, ignition temperature, total energy, thermal inertia and the heat of gasification. For the sake of this article, plastic, steel, concrete and wood are analysed in a bid to portray their behaviour in fire conditions. Plastic is a highly flammable material whose ignitability is higher than that of wood and cellulosic materials. Small flames are worth igniting plastic and render it vigorously burning at approximately 0.6m/s. The smoke produced is a combination of very dense black smoke with a sooty appearance due to flammability inhibition chemicals. During combustion, plastics produce highly toxic gases with the major one being carbon monoxide. Due to the melting action, plastics usually flow and produce dripping flames which are difficult to extinguish. It is therefore vital for designers to avoid this material whenever possible (National Fire Protection Association, 2008). Timber is a renewable and sustainable material that is composed of cellulose, lignin and hemicellulose. When heated, this material experiences thermal degradation which results to combustion thereby producing gases, tars, vapours and char. Increase in temperature results to carbonaceous char, tar and volatile gases. The decomposition process begins with hemicellulose at around 180 – 350°C which is then followed by cellulose at 275 – 350°C, and lastly lignin at temperatures of around 250 – 500°C. The dehydration of timber forms char which is a non-volatile residue enriched with carbon. The imparting of carbon on timber only increases the thermal resistance depending on the rate and temperature of heating. Smoke production of timber is estimated at 25–100 m2 kg-1 with a high rate of toxic gases emanation (Lowden & Hull , 2013). While steel materials do not exhibit the properties that plastic and timber possess, most analyses carried out indicate a strength change at various temperatures of exposure. Depending on the load, cross sectional capacity and the composition a steel structure is likely to withstand a considerable magnitude of buckling. Elevated temperature influence steel behaviour in four levels i.e. loss of strength and stiffness during the linear elastic phase in which the relationship between stress and strain eventually becomes nonlinear. Thermal creep at advanced temperatures influences the cross-sectional stress capacity of metallic structural members. The temperature dependency factors that lead to nonlinear stress-strain relationships go beyond the elastic range and lastly the plastic yield phase in which rapid deformation occurs and rupture in material without any sign or warning (Pauli, 2012). Concrete structures have been found to perform very well in event of fire due to their high temperature resistance properties. It has however been established that inasmuch as concrete exhibits fire resistance properties, losses in compressive strength and spalling is inevitable. The fact that concrete is a nonhomogeneous material that consists of composite cement and aggregate most often reinforced by steel renders its definition or modelling difficult. The difference in constituent materials differ across various industries thus there is no standard behaviour for concrete. It has however been demonstrated that losses in vapour lead to pressure build-up and eventual losses in compressive strength. Transformation of these properties is not a reversible process due to changes in chemical composition of the principle material; cement (Fletcher, et al., 2007). Failure Modes While material failure is not restricted to disintegration of fracturing, change in shape, alteration of mechanical properties and material loss can be considered. Failure occurs due to environmental conditions such as high energy, temperature and corrosion or even loads to which a structure is exposed to. Ultimate material failure however occurs in such conditions combining these factors. Some of the most common modes of failure have been identified in forms such as corrosion, fatigue, fracture and wear. Figure 1: Appearance of a brittle fracture (Craig, 2005). Brittle fractures are usually caused by ultimate tensile loading which causes a material to be split into two separate parts without necessarily undergoing the plastic deformation phase. Materials prone to this kind of failure are characterised by cracks, inclusions, notches, residual stresses and voids. Failure of this kind is catastrophic and has been observed in materials such as hard metals and ceramics (Craig, 2005). Ductile failures on the other hand have been observed in materials that elastically accommodate loads to yield point thereby rendering the attained shape permanent. The deformation of such materials is characterised by ductile fractures which are brought about unsustainable loads as shown in the diagram in figure 2 below. This usually occurs in materials with high ductility index such as copper and steel (Craig, 2005). Figure 2: Ductile cup cone (University of Southampton, 2013). Creep failure is a temperature dependent type of failure which is characterised by dimensional change in such conditions as stressed ones. These changes render the material insufficient to hold any load thus leading to rupture due to stress. Further, the microstructure of a material is said to migrate into the grain boundaries oriented to the direction of applied stress. Thermal creep is activated at various temperatures for different materials – thus this is not a standard behaviour for all materials. For example, most super alloys are susceptible to creep at temperature of between 1000 - 1200°C while tin soldier gives in to this mode of failure at 25°C (Craig, 2005). Another mode of failure worth highlighting in this report is fatigue. Fatigue is inflicted by sudden stress levels that are far much beyond the stress limit of a material. This form of failure attributes to a large number of failures across structural engineering – approximately 90%. Materials exposed to cyclic loads are more prone to this kind of failure due to sudden excesses in cyclic stress. Failure occurs in three phases namely; crack commencement, crack spread, and lastly material rupture. Figure 3: Fatigue failure in cyclic components (Reliability Edge, 2014). Signs and Hazards of Collapse in Construction Cracks in concrete reinforced with steel mainly brought about by environmental condition coupled by shrinkage and other predictable behaviours. Shrinkage cracks which occur in beams slabs and walls for example are hazardous and if left unattended might result into catastrophe. Another sign of collapse is temperature cracks which occur due to temperature variances. Since reinforcing steel is not likely to budge, concrete shrinks and eventually cracks posing as a danger to the inhabitants. Tension cracks are on the other side caused when beams are forced to bend due to tensional forces in reinforcing steel (Chanter & Swallow, 2007). Diagonal tension cracks have been identified to occur in zones with high beam and girders under normal vertical loads. These are usually brought about by tremors and periodical earthquakes. Unreinforced concrete walls have been observed to contain these cracks between the openings. On the other hand masonry walls characterised by brittleness have been observed to frequently give in to this kind of failure. Smoothness in joints as well as adding clamping and dowel joints on vertical bars is positioned as the best solution for this problem (Chanter & Swallow, 2007). There are three forms of identifiable hazard namely; falling, collapse among others. Falling hazards indicate dangers from falling debris or loosened materials due to the identified forms of failure. Collapse is also identified as a hazard that is worth being attended to due to its nature of stability loss and abrupt falling. It is also important to consider other forms of hazards such as asbestos, toxic gas, carbon monoxide, and other hazardous substances that may be part of a construction (Chanter & Swallow, 2007). List of References Chanter, B. & Swallow, P., 2007. Hazard identification and building monitoring. Oxford: John Wiley & Sons. Chibbaro, M., 2009. Construction Fire Safety: Phase by Phase. [Online] Available at: http://magazine.sfpe.org/fire-protection-design/construction-fire-safety-phase-phase [Accessed 1 May 2014]. Craig, B. D., 2005. Material Failure Modes, Part I. The AMPTIAC Quarterly, 9(1), pp. 9-16. Fletcher, I. A. et al., 2007. Behaviour Of Concrete Structures In Fire. Thermal Science, 11(2), pp. 37-52. Foy, G. F., 1969. Summary of Engineering Plastics. American Chemical Society, June, Volume 96, pp. 1-8. Lowden, L. A. & Hull , T. R., 2013. Flammability behaviour of wood and a review of the methods for its reduction. Fire Science Reviews, 2(4), pp. 1-19. National Fire Protection Association, 2008. Fire Protection Handbook. I ed. New York: National Fire Protection Association. Pauli, J., 2012. The behaviour of steel columns in fire, Zurich: Swiss Federal Institute of Technology Zurich. Reliability Edge, 2014. Reliability Prediction for Components in Fatigue. [Online] Available at: http://www.reliasoft.com/newsletter/v8i2/fatigue.htm [Accessed 2014 April 30]. Scotts Tool, 2007. What Are Thermoplastics?. [Online] Available at: http://www.scottstool.com/thermoplastic.htm [Accessed 30 April 2014]. Total Materials, 2010. True Stress - True Strain Curve: Part One. [Online] Available at: http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&NM=280 [Accessed 30 April 2014]. University of Southampton, 2013. Properties of Materials. [Online] Available at: http://www.southampton.ac.uk/~doctor/QS_4.htm [Accessed 30 April 2014]. Read More