Mechanical Properties PDF

Mechanical Properties Shearing Whenever the forces tend to cause one Stress and strain portion of the material to slide upon another adjacent to it the act...

Mechanical Properties Shearing Whenever the forces tend to cause one Stress and strain portion of the material to slide upon another adjacent to it the action is Stress is measured in pounds (or other called a shear. unit of weight or force) Unit stress – is the stress on a unit of Stiffness vs. flexibility the sectional area. Stiffness is the property by means of ex. If a load of 100 pounds is uniformly which a body acted upon by external supported by a vertical post with a forces tends to retain its natural size cross-sectional area of ten square and shape or resist deformation. Ex. A inches. What is the compressive material that is difficult to bend or stress? otherwise deform. Strain is measured in inches (or other Flexible one that is easily bent or linear unit). otherwise deformed. It is not the exact counterpart of stiffness as it also Unit strain – the strain per unit of involves toughness and pliability. length. Ex. A post 10 inches long before compression is 9.9 inches long under the compressive stress, Mechanical property terms what is the total strain? And unit strain? Elastic – when the body completely regains its original form upon release of 3 kinds of internal stress stress. Tensile Elastic limit – the limit beyond which it Compressive is impossible to carry the distortion of a shearing body without producing a permanent alteration in shape. Tensile Permanent set – beyond elastic limit When external forces act upon a bar in where the size and shape of the a direction away from its ends or a specimen after removal of the load will direct pull, the stress is a tensile stress not be the same as before and the – the stress is elongation difference or amount of change is called permanent set. Comprehensive When external force act towards the ends or a direct push it is compressive – the stress is shortening Resilience – the amount of work done Wood exhibits its greatest upon a body in deforming it. It is also a strength in tension measure of the potential energy stored parallel to the grain. In the material and represents the It is greatest in straight- amount of work the material would do grained specimens with upon being released from a state of thick-walled fibers stress. Mechanically property terms Compressive or crushing strength Plasticity – permanent set is due to the Compression across the grain – closely plasticity of the materials. related to hardness and transverse A perfectly plastic shear. substance would have no elasticity and the smallest The effect of compression across the forces would cause a set. grain is to compact the fibers, the load The plasticity of wood is gradually but irregularly increasing as increased by wetting, the density of the material is increased heating and especially by steaming and boiling. When wood is used for columns, props, Brittle – describes the property of a pots and spokes the weight of the load material that fractures when tends to shorten the material endwise. subjected to stress but has a little Also known as endwise compression tendency to deform before or compression parallel to the grain. rupture. Common ex are chalk and glass 𝑃 C= 𝐴 Sometimes the term brash is used to describe this condition in wood. Shearing Strength Whenever forces act upon a body in Modulus of elasticity – the measure of such a way that one portion tends to stiffness or aka coefficient of elaticity or slide upon another adjacent to it the young’s modulus. 𝒖𝒏𝒊𝒕 𝒔𝒕𝒓𝒆𝒔𝒔 action is called a shear. E = 𝒖𝒏𝒊𝒕 𝒔𝒕𝒓𝒂𝒊𝒏 It could be along the grain A large modulus indicates a or across the grain. stiff material The use of nails involves resistance to shear Tensile Strength across the gain. Or the steel edge of axe or Tension- results when a pulling force is hammer tends to cut off applied to opposite ends of a body. the handle The result is an elongation or stretching of the material in the direction of the applied force. The action is the opposite of compression. Knowledge of shear parallel to the grain greater is the liability of failure in is important since wood frequently fails horizontal shear before the ultimate in that way. strength of the beam is reached. The value of shearing stress parallel to the grain can be determined by: 3 common forms of beams 𝑃 𝑆ℎ𝑒𝑎𝑟 = 𝐴 Simple beam - bar resting upon two supports, one near each end Oblique shearing stresses are Cantilever beam - bar resting upon one developed in a bar when it is subjected support or that portion of any beam to direct tension or compression. The projecting out of a wall or beyond a maximum shearing stress occurs along support. a plane when it makes an angle of 45 degrees with the axis of the specimen. Continuous beam - bar resting upon In this case: 𝑃 more than two supports. 𝑠ℎ𝑒𝑎𝑟 = 2𝐴. When the angle θ is less than 45 degrees, the shear along the 𝑃 plane = 𝐴sin θ cos θ Stiffness of beams modulus of eLasticity (E) or measure of When external forces acting in the stiffness of a rectangular prismatic same plane are applied at right angles simple beam loaded at the centre and to the axis of a bar so as to cause it to resting freely on supports at either end bend, they occasion a shortening of the is: longitudinal fibers on the concave side 𝑃′ 𝑙 3 𝐸= and an elongation of those on the 4𝐷𝑏ℎ3 convex side. b= width of beam h = height or depth of Transverse shear – the external forces beam, inches. acting to bend the bar also tend to L = span (length between rupture it at right angles to the neutral points of supports) of plane by causing one transverse beam) inches. section to slip past another. D = deflection produced - This stress at any point is equal by load l”, inches. to the resultant perpendicular to P’ = load at or below the axis of the forces acting at elastic limit, pounds. this point, and is termed the transverse shear (or in the case The measure of the breaking strength of beams, vertical shear). of a beam is expressed in terms of unit stress by a modulus of rupture, which is longitudinal shear (or in the case of a purely hypothetical expression for beams, horizontal shear). - tending to points beyond the elastic limit. move the fibers past one another in an axial direction. It is maximum at the neutral plane and decreases to zero at the outer elements of the section. The shorter the span of a beam in proportion to its height, the Kinds of Loads Cleavability Uniform load - occurs where the load is Cleavability is the term used to denote spread evenly over the beam. the facility with which wood is split. Concentrated load - occurs where the This property of wood is very important load is applied at single point or points. in certain uses such as firewood, fence rails, billets, and squares. Resistance to Live or immediate load is one of splitting or low cleavability is desirable momentary or short duration at any one where wood must hold nails or screws, point, such as occurs in crossing a as in box-making. bridge. Creep and Duration of load Dead or permanent load is one of constant and indeterminate duration, as Creep and duration of load—Time- books on a shelf. dependent deformation of wood under load. If the load is sufficiently high and the Toughness or torsion duration of load is long, failure (creep– rupture) will eventually occur. Toughness is a term applied to more The time required to reach rupture is than one property of wood. Thus wood commonly called duration of load. that is difficult to split is said to be tough. Duration of load is an important factor - is one that will not rupture until it in setting design values for wood. has deformed considerably under loads at or near its maximum strength, or one which Fatigue still hangs together after it has been ruptured and may be bent Fatigue—Resistance to failure under back and forth without breaking specific combinations of cyclic loading apart. conditions: frequency and number of cycles, maximum stress, ratio of maximum to minimum stress, and other The torsion or twisting test is useful in less-important factors. determining the toughness of wood. Rolling shear strength Hardness Shear strength of wood where shearing resistance to indentation, and force is in a longitudinal plane and is resistance to abrasion or scratching. acting perpendicular to the grain. Tests for indentation are commonly shear stress acting on the radial– made by penetrations of the material tangential plane perpendicular to with a steel punch or ball. grain. Tests for abrasion are made by wearing down wood with sandpaper or by means of a sand blast. Fracture toughness—Ability of wood to Bending strength withstand flaws that initiate failure. Measurement of fracture toughness The ability of wood to resist load helps identify the length of critical flaws causing it to bend. that initiate failure in materials. The bending caused by load is called deflection Timber Mechanics TIMBER MECHANICS is a branch of wood science which deals with the Static - refers to a material's ability to energy and forces and their effects on withstand applied loads or forces when wood structure. they are applied slowly and steadily over time. - The expression of the behavior of wood under applied forces is called MECHANICAL Impact bending strength - material's PROPERTY/ strength property ability to withstand sudden and dynamic loads or forces that are applied - Mechanical Properties – are rapidly. This might include the capacity related to the strength qualities of wood to resist impact loads, such as or characteristic of wood, i.e., those experienced in situations like static bending (MOR/elasticity), dropping heavy objects on wooden compression, hardness, surfaces. shearing strength and tension. Strength values: The factors affecting the mechanical or 1. Work to proportional limit – wood strength property of wood absorbs shock without causing permanent damage. 1. Wood defect 2. Specific gravity 2. Work to Maximum Load – wood 3. Moisture content absorbs shock causing some 4. Temperature permanent damage. 5. Duration of load 3. Modulus of Elasticity – wood recovers its original shape and size Wood advantages as building materials after stress is removed. 1. Strong for its weight 4. Modulus of Rupture – wood resists to 2. Easy to cut in various shapes its tolerable bending and when excess 3. Easy to fasten with nails, bolts, etc. to stress applied might cause failure. 4. Resilient, tough, and elastic Compressive strength Toughness - (Shock resistance) – the ability or capacity of wood to absorbs - the ability of wood to resist shock energy. crushing due to applied force tending to shorten the wood Stiffness – the ability of wood to retain elements. its natural size and shape when acted on by an externally applied load. Shearing strength - The ability of wood to resist a force causing one part of the material to slip on adjacent part. A force that exerts on wood that causes it to slip is called SHEARING STRENGTH. The types of shears are: 1. Horizontal shear – slip upon a contiguous part in the direction of the grain. 2. Oblique shear – slip at an angle to the long axis of wood. 3. Endwise shear – slip on a contiguous part along a plane parallel to the grain. 4. Sidewise shear – slip on a contiguous part along a plane perpendicular to the grain. 5. Vertical shear – slip in the direction of the force lines represented by the loads and reactions. Shearing strength - The ability of wood to resist a force causing one part of the material to slip on adjacent part. Hardness – the ability or capacity to resist indentation or force. Tensile strength - the ability of wood to resist deformation due to applied force tending to pull the wood apart. Mechanics- a branch of physical Study of the mechanical properties of science that deals with energy and a material is concerned mostly with its forces and their effect on bodies. behavior in relation to stresses and strains, and the factors affecting this the practical application of mechanics behavior. to the design, construction, or operation of machines or tools. Rheology - a science dealing with the Stress deformation and flow of matter also : A stress is a distributed the ability to flow or be deformed. force and may be defined as the mutual action (1) of Orthotrophic- In contrast to metals and one body upon another, plastics, wood is an orthotropic material, or (2) of one part of a meaning its properties will be independent body upon another part. in three directions – longitudinal, tangential In the first case the stress and radial is external; in the other internal. The same stress Viscoelasticity - which can be described may be internal from one as having both plastic and elastic point of view and external characteristics when exposed to a from another. certain deformation. Stress is the force applied to a material, Elastic materials easily stretch under divided by the material's cross- an applied load. However, they return to sectional area. their original conditions once the load is force per unit area within materials that released. arises from externally applied forces, uneven heating, or permanent In contrast, plastic materials stay at the deformation and that permits an stretched condition even if the load is accurate description and prediction of released after a long period time. elastic, plastic, and fluid behaviour. Mechanical Properties - The If no external forces act upon a body its mechanical properties of wood are its particles assume certain relative fitness and ability to resist applied or positions, and it has what is called its external forces. natural shape and size. If sufficient external force is applied the external force is meant any force natural shape and size will be changed. outside of a given piece of material This distortion or deformation of the which tends to deform it in any manner. material is known as the strain. The amount of deformation such properties determine the use of experienced by the body in the wood for structural and building direction of force applied, divided by purposes and innumerable other uses the initial dimensions of the body. of which furniture, vehicles, implements, and tool handles are a few common examples. Fundamental Considerations and definitions Stress and Strain Every stress produces a corresponding strain, and within a certain limit the strain is directly proportional to the stress producing it. The same intensity of stress, however, does not produce the same strain in different materials or in different qualities of the same material. No strain would be produced in a perfectly rigid body, but such is not known to exist. Stress - is the force applied to a material, divided by the material’s cross-sectional area. Stress - is the force applied to a material, divided by the material’s cross-sectional area. This stress-strain relationship is known as Hooke’s Law, and in this region, the slope of the stress-strain curve is referred to as the modulus of elasticity (aka Young’s modulus), denoted E.  oriented nature of the Philippine Furniture- refers to movable objects furniture industry. intended to support various human activities such as seating, sleeping, and Skills Development:Ensuring a working. skilled workforce is crucial for maintaining the quality and competitiveness of the industry. Secondary wood products refer to items Ongoing efforts in training and skills that are manufactured from wood but development are essential to address are not part of the primary lumber or this concern. timber products like boards, beams, or planks Design Innovation:Keeping up with design trends and innovation is essential for attracting consumers, both Philippine wooden industry as an locally and internationally. Investments export industry -should meet the in design research and development following conditions: can contribute to the industry's growth. Strengthening of export marketing activities. Improving the performance of the Infrastructure and Logistics:Efficient industry and firms transportation and logistics are crucial for the timely delivery of products. COMMON ISSUES IN Furniture Improvements in infrastructure can INDUSTRY contribute to the industry's overall efficiency and competitiveness. Sustainability and Deforestation:The logging and harvesting of wood for Market Access and Export furniture production can contribute to Challenges:The industry's success is deforestation if not managed often tied to export markets. Addressing sustainably. issues related to trade barriers, market access, and compliance with Illegal Logging:The Philippines, like international standards is essential for many other countries, faced challenges sustained growth. related to illegal logging. This not only poses environmental issues but also affects the competitiveness of legal and COMMON SECONDARU WOOD ethical businesses within the industry. PRODUCTS COMMON IN PHILIPPINES Competition with Other Materials:The furniture industry faces competition from alternative materials Plywood such as metal, plastic, and engineered Particleboard wood. The industry needs to adapt to Medium density Fiberboard (MDF) changing consumer Oriented Strand Board Wooden Veneer Global Market Dynamics:Changes in Wooden Laminates global demand and market dynamics, such as economic fluctuations and Wood-Plastic Composites (WPC) trade policies, can impact the export- Finger-Jointed Wood Products Wood Pellets  Moldings and Trim -Various decorative and functional moldings and trim pieces, such as baseboards, crown moldings, and chair rails, are often made from processed wood materials. Wooden flooring -Engineered wood flooring and laminated wood flooring are produced in the