Properties of AB Materials PDF

Intended for BSABE 3A, 3B, 3C  I. Physical properties  II. Mechanical properties  III. Optical properties  IV. Acoustic properties  V. Frictional properties  VI. Electrical properties  VII. Thermal properties  VIII. Nondestructive quality determination of AB products  Durables – includes...

Intended for BSABE 3A, 3B, 3C  I. Physical properties  II. Mechanical properties  III. Optical properties  IV. Acoustic properties  V. Frictional properties  VI. Electrical properties  VII. Thermal properties  VIII. Nondestructive quality determination of AB products  Durables – includes cereals, grains and legumes  Perishables – includes fruit, vegetables, root and bulb crops, cutflower, herbs, and medicinal crops.  Cashew  Mango  Sweet potato  Coconut  Pineapple  Important in designing particular equipment prior to the behavior of the product upon handling.  The shape is considered in calculation of various cooling and heating loads of food materials.  The frontal area and diameters are essential for determination of terminal velocity, Reynold’s number, and drag coefficient.  The density and specific gravity are needed for calculating the thermal diffusivity in heat transfer operations.  Size, shape, volume, surface area, density – Fruits and vegetables are usually graded based on size, shape and density. Impurities in food materials are separated by density.  Bulk density – necessary to estimate floor space during storage and transportation.  Surface area of commodity – important in investigations related to spray coverage, removal of residues, respiration rate, light reflectance, and color evaluation, heat transfer studies in heating and cooling processes.  Volume change and porosity – important parameters in estimating the diffusion coefficient of shrinking systems.  Porosity – used to calculate effective diffusivity during mass transfer processes  What else?  Size can be measured using the projected area method. The three dimensions commonly measured includes: 1. Minor diameter – shortest dimension of the minimum projected area. 2. Major diameter – longest dimension of the maximum projected area. 3. Intermediate diameter – the minimum diameter of the maximum projected area or the maximum dimeter of the minimum projected area.  Indexes used to characterize a given shape: 1. Roundness 2. Roundness ratio 3. Sphericity 4. Axial ratio 5. Degree of inequality of projected areas  Roundness ratio is the ratio of the radius of the smallest circle, to the mean radius of the object. 𝑅𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑐𝑢𝑟𝑣𝑎𝑡𝑢𝑟𝑒, 𝑟, 𝑜𝑓 𝑡ℎ𝑒 𝑠ℎ𝑎𝑟𝑝𝑒𝑠𝑡 𝑐𝑜𝑟𝑛𝑒𝑟 𝑅𝑜𝑢𝑛𝑑𝑛𝑒𝑠𝑠 𝑟𝑎𝑡𝑖𝑜 = 𝑀𝑒𝑎𝑛 𝑟𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒, 𝑅  Roundness- it is a measure of the sharpness of the solid material. 𝑙𝑎𝑟𝑔𝑒𝑠𝑡 𝑝𝑟𝑜𝑗𝑒𝑐𝑡𝑒𝑑 𝑎𝑟𝑒𝑎 , 𝐹𝑚 Roundness = 𝐴𝑟𝑒𝑎 𝑜𝑓 𝑠𝑚𝑎𝑙𝑙𝑒𝑠𝑡 𝑐𝑖𝑟𝑐𝑢𝑚𝑠𝑐𝑟𝑖𝑏𝑖𝑛𝑔 𝑐𝑖𝑟𝑐𝑙𝑒, 𝐹𝑐 The shape of an irregular object can be described by terms such as the following: Shape Description Round Approaching spheroid Oblate Flattened at the stem end and apex Oblong Vertical diameter greater than the horizontal diameter Conic Tapered toward the apex Ovate Egg-shaped and broad at the stem end. Elliptical Approaching ellipsoid. Truncate Having both ends squared or flattened. Unequal One half larger than the other. Regular Horizontal section approaches a circle. Irregular Horizontal cross section departs materially from a circle.  Sphericity is the ratio of the diameter of a sphere of the same volume as that of the particle and the diameter of the smallest circumscribing sphere or generally the largest diameter of the particle. This parameter shows the shape character of the particle relative to the sphere having same volume. 𝐷𝑒 Sphericity = 𝐷𝑐 Where: De = diameter of a sphere having same volume as that of the particle Dc = diameter of the smallest circumscribing sphere - The platform scale is a simple technique which is commonly used for determination of volume of large materials like fruits and vegetables. The weight of material is determined by weighing on the scale in air, thereafter, the material is forced into the water with the help of a rod. The later reading of the scale while the material is submerged minus the weight of container and water is the actual weight of the displaced water. The volume density and specific gravity of the material are estimated by following formulae.  It is the measure of void space between the materials  Porosity is the percentage of the total volume occupied by the air  Total volume – Volume occupied by particle/sample +Volume occupied by air  Size, shape, volume, surface area, density – Fruits and vegetables are usually graded based on size, shape and density. Impurities in food materials are separated by density.  Bulk density – necessary to estimate floor space during storage and transportation.  Surface area of commodity – important in investigations related to spray coverage, removal of residues, respiration rate, light reflectance, and color evaluation, heat transfer studies in heating and cooling processes.  Volume change and porosity – important parameters in estimating the diffusion coefficient of shrinking systems.  Porosity – used to calculate effective diffusivity during mass transfer processes  1. Boundary volume – volume of a material considering the geometric boundary. It can be measured by buoyancy force (liquid,gas, or solid displacement); gas adsorption, can be estimated from the materials geometric dimensions.  2. Pore volume – volume of the voids or air inside a material  Density is defined as mass per unit volume. 𝑘𝑔 𝑚𝑎𝑠𝑠  𝜎( ) = 𝑚3 𝑣𝑜𝑙𝑢𝑚𝑒  True density – is the density of pure substance or a composite material calculated from its component densities considering conservation of mass and volume.  Material density – density measured when a material has been thoroughly broken into pieces small enough to guarantee that no closed pores remain.  Particle density – is the density of a particle which includes the volume of all closed pores but not the externally connected pores. In this case, the particle is not modified structurally, as in the case of material density.  Apparent Density - is the density of a substance including all pores remaining in the material.  Bulk Density - is the density of a material when packed or stacked in bulk. The bulk density of packed materials depends on the geometry, size, and surface properties of individual particles 1. Apparent density a. Geometric dimension method - This method is only suitable for liquid and soft materials, where no void exists in the packing. The density determination method consists of finding the mass of a frozen sample with a known volume. The unfrozen sample is placed in the cylindrical container and then frozen at the desired temperature. The excess frozen sample can be removed with a sharp knife. Then the cylinder and frozen sample should be weighed immediately. From the mass of the sample and the volume of the cylinder, density can be calculated.  buoyant force can be determined from sample weight in air and liquid. The apparent density can be calculated from the equation. 𝑚 𝜌𝑎 =𝜌𝑤 x 𝐺 where m and G are the mass (in kilograms) of the sample in air and liquid (i.e., water), respectively, and ρw is the density of the liquid. Top-loading balance for measurement of buoyant force for a Two errors may occur – 1st ( mass transfer from the sample lighter than sample to liquid); 2nd ( due to partial floating) liquid  Mohsenin (1986) described a simple technique with a top-loading balance that applies to large objects such as fruits and vegetables. The sample is first weighed on the scale in air and then forced into water by means of a sinker rod. Second readings are then taken with the sample submerged. The density can then be calculated as: Analytical balance for  where G1 refers to the sinker plus the sample and G2 measurement of refers to the sinker only in water or liquid. m and G buoyant force are the mass (in kilograms); ρw is the density of the liquid  In the case of coated sample with a sinker, the following equation can be used:  where G1 refers to the sinker plus the wax-coated sample, G2 the sinker only, and G3 the wax only. G3 can be calculated as:  Liquid Displacement Method. The volume of a sample can be measured by direct measurement of volume of liquid displaced. The difference between the initial volume of the liquid in a measuring cylinder and the volume of the liquid plus immersed material (coated) is the volume of the material.  Gas Pycnometer Method - Different commercial gas pycnometers for volume measurement are available. The gases air, nitrogen, and helium can be used. Mohsenin (1986) described a method to measure volume using high- pressure air  Solid Displacement Method. The apparent volume of an irregular solid can be measured by a solid displacement or glass bead displacement method. Glass beads have an advantage over sand due to their uniform size and shape, thus producing reproducible results.  A. Pycnometer method - Material density can be measured when a material is ground enough to guarantee that no closed pores remain. Both liquid and gas displacement methods (pycnometer) can be used to measure the volume of ground material.  B. Mercury Porosimetry - Pore volumes can be measured by gas adsorption techniques or mercury porosimetry. Mercury porosimetry is suitable for measurement of smaller open pores since it uses high pressure. In the case of mercury porosimetry for material density, the sample need not be ground since high pressure forces mercury to penetrate into the pores.  C. Gas Adsorption method - In the gas adsorption method, the sample is cooled, usually to cryogenic temperatures, and then is exposed to the inert adsorptive gas, typically nitrogen, at a series of precisely controlled pressures. As the pressure increases, a number of the gas molecules are adsorbed onto the surface of the sample.  Particle density can be measured by the volume displacement method used in apparent density measurement without coating the particle or object.  Bulk density can be determined by stacking or placing a known mass of particles into a container of known volume, such as a measuring cylinder. This method considers all pores inside as well as outside the individual particles. After the excess has been removed, the mass of the sample can be measured and the bulk density can be calculated.  1. Boundary surface area is mainly estimated from geometric dimensions or measured by image analysis or contour analysis. Leaf and stalk surface area are measured by contact-printing the surface on a lightsensitive paper and then estimating the area with a planimeter, or by tracing the area on graph paper and counting the squares or determining the mass of the paper. In this method, the mass-area relationship of the paper should be developed first. Another method is the use of an air-flow planimeter, which measures the area as a function of the surface obstructing the flow of air (Mohsenin, 1986).  The surface area of fruits and vegetables can be estimated from the peeled or skin area. In this method, fruit is peeled in narrow strips and the planimeter sum of the areas of tracings of the strips is taken as the surface area. Similarly, strips of narrow masking tape can be used to cover the surface; from the length and width of the tape, the surface area can be estimated. A transient heat transfer study can also be used to estimate the surface area (Mohsenin, 1986).  The simplest method of obtaining the surface area of a symmetrical convex body such as an egg is the projection method using a shadow graph or photographic enlarger. Using the profile of the egg, equally spaced parallel and perpendicular lines can be drawn from the axis of symmetry to the intersection with the profile. Then using manual computation, by integration, the surface area can be obtained by summing up the surfaces of revolution for all of the divided segments (Mohsenin, 1986).  Pore surface area can be defined as the surface of the pores in a porous medium exposed to fluid flow either per unit volume or per unit mass of the solid particles. a. Methods Based on Adsorption - The quantity of an inert vapor that can be adsorbed on the pore surface is dependent on the area of the surface. The quantity of a gas or vapor adsorbed is proportional to a surface area that inclines the tiny molecular interstices of the porous material, whereas the surface area pertinent to fluid flow does not include this portion of surface area.  Methods Based on Fluid Flow This method is more commonly used for rocks and is not suitable for fragile solids, such as foods. Also, the surface of dead-end pores cannot be included in the fluid flow method.  Mercury intrusion measures the characteristics of pores. Surface area is determined from the intruded volume using geometric dimensions of a preassumed geometric shape of the pores.  Cross-sectional area is the area of a surface after longitudinal or transverse section of a material. It is necessary when fluid is flowing over an object. The methods of boundary surface area can also be used.  1. Vernier caliper  2. Micrometer caliper  Porosity indicates the volume fraction of void space or air in a material and is defined as: 𝐴𝑖𝑟 𝑜𝑟 𝑣𝑜𝑖𝑑 𝑣𝑜𝑙𝑢𝑚𝑒 Porosity = 𝑇𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒  Different forms of porosity: 1. Open pore porosity 2. Closed pore porosity 3. Apparent porosity 4. Bulk porosity 5. Bulk particle porosity 6. Total porosity 1. Open pore porosity – The volume fraction of pores connected to the exterior boundary of a material. 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑜𝑝𝑒𝑛 𝑝𝑜𝑟𝑒 Open ore porosity = 𝑡𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝜌𝑎 𝜀𝑜𝑝 = 1 − 𝜌𝑝 2. Closed pore porosity - is the volume fraction of pores closed inside the material and not connected to the exterior boundary of the material. 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑐𝑙𝑜𝑠𝑒𝑑 𝑝𝑜𝑟𝑒𝑠 Closed ore porosity = 𝑡𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝜌𝑝 𝜀𝑐𝑝 =1− 𝜌𝑚 3. Apparent porosity - is the volume fraction of total air or void space in the material boundary and is defined as (εa = εop + εcp): 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑎𝑙𝑙 𝑝𝑜𝑟𝑒𝑠 Apparent porosity= 𝑡𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝜌𝑎 𝜀𝑎 = 1 − 𝜌𝑚 4. Bulk porosity - is the volume fraction of voids outside the boundary of individual materials when packed or stacked as bulk: 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑣𝑜𝑖𝑑𝑠 𝑜𝑢𝑡𝑠𝑖𝑑𝑒 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙𝑠 𝑏𝑜𝑢𝑛𝑑𝑎𝑟𝑦 Bulk porosity= 𝑡𝑜𝑡𝑎𝑙 𝑏𝑢𝑙𝑘 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑡𝑎𝑐𝑘𝑒𝑑 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙𝑠 𝜌𝑏 𝜀𝐵 = 1 − 𝜌𝑎 5. Bulk particle porosity - is the volume fraction of the voids outside the individual particle and open pore to the bulk volume when packed or stacked as bulk. 𝜀𝐵𝑃 = 𝜀𝐵 + 𝜀𝑜𝑝 6. Total Porosity - Total porosity is the total volume fraction of air or void space (i.e., inside and outside of the materials) when material is packed or stacked as bulk.  1. Direct method - In this method, the bulk volume of a piece of porous material is measured first, and then the volume is measured after compacting the material to destroy all its voids. Porosity can be determined from the difference of the two measured volumes. This method can be applied if the material is very soft and no repulsive or attractive force is present between the surfaces of solid particles.  2. Optical Microscopic method - In this method the porosity can be determined from the microscopic view of a random section of the porous medium. This method is reliable if the sectional (two- dimensional) porosity is same as the three-dimensional porosity. Image analysis is necessary to estimate the surface area of pores.  3. Density method - pore volume can be measured directly by liquid or gas displacement methods  Mechanical properties - defined as those which affect the behavior of the agricultural material under the applied force. The mechanical properties such as hardness, compressive strength, impact and shear resistance and the rheological properties affect the various operations of agricultural processing  Useful for application in designing equipment for milling, handling, storage, transportation, food processing etc.  The impact and shear resistance are important for size reduction of food grains. This information is useful in determination of the appropriate methods of crushing, breaking or grinding the grains. These properties also play important roles towards seed resistance to cracking under harvesting and threshing conditions. Stress is measure of an external force acting over the cross sectional area of an object. Stress has units of force per area: N/m2 or lb/in2. Types of stress: 1. Compressive stress – directed toward the material 2. Tensile stress – directed away from the material. 3. Shearing stress – directed tangentially to the material.  Stress can act on food at different mechanical situations: 1. Static – constant stress/strain 2. Dynamic – varying stress/strain 3. Impact – stress exerted and removed after a short period of time. Solid foods are mechanically characterized by compression tests or impact tests. Equipment used: Universal Testing Machine Material Testing Equipment   Elastic Deformation – This deformation is temporary and is recovered as soon as the load is Typical stress-strain curve removed. The sample returns to its original size. Depending on the type of plastic, some time- dependent elastic and plastic deformation (anelasticity and creep) may accompany the initial elastic deformation of the specimen.  Yielding– This marks the end of the initial elastic region and the start of plastic deformation and in some cases the onset of necking   Strain Softening – Following yielding some materials will appear to soften (load decreases) as a neck forms and the structure begins the Typical stress-strain curve transformation from one of randomly oriented chains and crystallites into a more aligned structure.  Cold Drawing – The crystallites are rotating and being reoriented. Most of this is happening in the zone where the neck is forming. Strain  Hardening – Once the specimen’s structure is fully drawn the stress increases again. This new structure is now resisting deformation.  Fracture – The specimen finally breaks.  1. Uniaxial compression/tension test –In this test, a sample with a convenient geometry (e.g., cylinder or rectangular prism) is subjected either to a deformation or to a force, and the corresponding force or deformation is recorded. If the magnitudes of force and deformation are small, then the body may be assumed to be elastic. The resultant stress (σ) and strain (∈) may be calculated as 𝐹 𝜎=𝐴 ∆𝐿 ∈= 𝐿 where F is the force, A is the cross-sectional area of Uniaxial compression, shear, the body, ∆L is the deformation, and L is the original length of the body and isotropic (bulk) compression of an elastic solid  Morrow and Mohsenin (1968) divided the methods of dynamic testing into four types: (1) direct measurement of stress and strain (2) resonance methods (3) wave propagation methods, and (4) transducer methods.  Resonance methods have been used primarily for determining resonant frequencies and thereby also determining Young’s modulus, shear modulus, loss coefficient, etc., at the resonant frequency.  In direct stress–strain tests, a linear viscoelastic material (most foods show this behavior to some extent) is subjected to a sinusoidally varying strain, and the resulting stress as a function of time is observed. If a material is subjected to a strain variation, such that  Rheology is a science devoted to the study of deformation and flow.  The mechanical and rheological properties are measures of how materials respond when they are deformed. Solids are characterized by mechanical properties such as the Young's modulus, strength and hardness, whereas liquids are characterized by rheological properties such as the viscosity and yield stress  A material can deform in 3 ways: elastic, plastic or viscous. 1. Elastic deformation  Young’s modulus, E 2. Plastic deformation: deformation does not occur as long as the stress is below a limit value of yield stress. Deformation is permanent. 3. Viscous deformation: deformation (flow) occurs instantly with the application of stress and it is permanent. The rate of strain is proportional to the stress 1. Normal strain - change in length per unit length in the direction of the applied normal stress. ∆𝐿 𝜀= 𝐿 2. Shear strain - defined as the change in the angle formed between two planes that are orthogonal prior to deformation as a result of the application of stress. 𝑑 𝛾 = 𝑡𝑎𝑛𝜃 = 𝑡  Pure elastic behavior is defined such that when a force is applied to a material, it will instantaneously and finitely deform; and when the force is released, the material will instantaneously return to its original form. Such a material is called a Hookean solid.  Elastic modulus is the ratio of stress to strain in a material, where stress is equal to force per unit area and strain is the observed deformation due to the force, divided by the original length of the material.  Modulus of elasticity (E) - The modulus calculated by applying a force perpendicular to the area defined by the stress. 𝜎 E= 𝜀  Plastic strain - strain that is not recovered during unloading.  Elastic strain - strain that is recovered during unloading.  Degree of plasticity - the ratio of plastic strain to total strain when a material is loaded to a certain load and unloaded.  Degree of elasticity - the ratio of elastic strain to total strain  Shear or modulus of rigidity (G) - The modulus calculated by applying a force parallel to the area defined by the stress, or a shearing force. 𝜏 G= 𝛾  Bulk modulus (K)- If the force is applied from all directions (isotropically) and the change in volume per original volume is obtained.  Poisson’s ratio (µ):  When a material is compressed in one direction, it usually tends to expand in the other two directions perpendicular to the direction of compression.  The Poisson ratio is the ratio of the fraction (or percent) of expansion divided by the fraction (or percent) of compression, for small values of these changes.  Coefficient of viscosity - is defined as the shearing stress applied divided by the resulting rate of strain. In this way, it is very similar to the modulus for Hookean solids.  Newtonian liquid - This liquid flows infinitely until the force is removed, and upon removal of the force, it has no ability to regain its original state.  Bioyield point is defined as the point at which an increase in deformation is observed with a decrease or no change of force. Bioyield point is an indication of initial cell rupture. Corresponds to a failure in the microstructure of the sample.  Rupture point - point on the stress- strain or force-deformation curve at which the axially loaded specimen ruptures under a load. Corresponds to a failure in the macrostructure of the specimen.  Stress-strain curve determines how a material behaves how it has a relationship between the strain and stress for a given material. We apply a force on a material cylinder and record the change in length at various applied forces to cause the strain.  Ultimate strength point (point D) – The point up to which tells the maximum stress a material can withstand.  Breaking point ( point E) – the point of rupture or fracture.  The ultimate strength and fracture points are far apart, then the material is ductile.  The ultimate strength and fracture points are close to each other then the material is brittle.  Different material properties:  Ductile – the ability of a amterial to be plastically deformed without fracture is called ductility.  Brittle – the element that is hard but breaks easily with very less force is called brittle material.  Malleable – The property of a material that helps to form thin sheets either by rolling or hammering.  Lustrous – the shiny surface materials.  Uniaxial Compression – A popular method of testing for agricultural product/food material.  Tensile loading – less common than compression testing for agricultural product/food material. Suitable for testing packaging materials.  Bending tests – can be used for determination of the critical tensile stresses at failure  Torsional loading  1. Uniaxial compression/tension test –In this test, a sample with a convenient geometry (e.g., cylinder or rectangular prism) is subjected either to a deformation or to a force, and the corresponding force or deformation is recorded. If the magnitudes of force and deformation are small, then the body may be assumed to be elastic. The resultant stress (σ) and strain (∈) may be calculated as 𝐹 𝜎=𝐴 ∆𝐿 ∈= 𝐿 where F is the force, A is the cross-sectional area of the body, ∆L is the deformation, and L is the original length of the body Uniaxial compression, shear, and isotropic (bulk) compression of an elastic solid