Plastics Engineering

Plastics

Craftech Industries, 2013 Engineering 8 Dock Street, Hudson, NY 12534 Website: www.craftechind.com Dictionary of Manufacturing Terms Blog: info.craftechind.com/blog E-mail: [email protected] Phone: 518-828-5001 or 800-833-5130 Fax: 518-828-9468 ABS See Acrylonitrile butadiene styrene.

Abrasion resistance is the ability of a material to tolerate mechanical action by means of friction such as rubbing, scrapping etc. and helps maintain the original appearance of the part.

Acetal forms when the hydroxyl group is lost as water. The ion that is produced is then rapidly attacked by a molecule of alcohol. Loss of the proton from the attached alcohol creates the acetal. Alkynes in organic chemistry are an unsaturated hydrocarbon containing one Acrylonitrile butsdiene styrene (ABS) carbon-carbon triple bond between two atoms. is a common thermoplastic polymer. Its glass Like other hydrocarbons, alkynes are generally transition temperature is approximately 105°C hydrophobic (see hydrophobic) but tend to be (221°F). ABS is amorphous and therefore has no more reactive. true melting point. ABS is a terpolymer, made by polymerizing styrene and acrylonitrile in the Aliphatic hydrocarbons are made up of presence of polybutadiene. carbon and hydrogen atoms joined together in straight chains, branched chains or nonaromatic Adhesive strength refers to the ability of rings such as white spirits and kerosene. an adhesive to adhere to a surface or bond two surfaces together. Amide groups are made up of a carbonyl group linked to a nitrogen atom. Amorphous Addition polymers involve the reaction of polymers’ molecular structure lacks a definite unsaturated monomers. Types of condensation repeating form. They have a glass transition polymers include polyamides, polyacetals and temperature but no definite melting point. polyesters. Amorphous Polymers have a molecular Additives include reinforcing fillers, like structure that lacks a continuous repeating form. fiberglass for strength, fillers added to create They have a glass transition temperature but no volume, plasticizers, flame retardants, colorants, definite melting point. UV resistance and many others. Most plastics are compounded from a resin and one or many Annealing is the process of heating a plastic additives. (See Craftech Industries Blog 10/27/14) gradually to above its glass transition point, maintaining that temperature for a specific Alkaline means having a pH greater than 7 and period of time and then allowing it to cool to a relatively low concentration of hydrogen ions. relieve internal stresses caused by manufacturing processes.

Antioxidants are molecules that inhibit other molecules from being oxidized.

2 COPYRIGHT©2016 CRAFTECH INDUSTRIES Antistatic Agents are compounds used Birefringent is the optical property of an to treat materials or their surfaces to reduce or anisotropic material whose refractive index eliminate the buildup of static. depends on the polarization and propagation direction of light. Aromatic Hydrocarbons have alternating double and single bonds between carbon Bond Strength is the degree to which atoms atoms that form rings found in petroleum. The linked together in a chemical bond contribute to configuration of six carbon atoms in aromatic one another’s valency. compounds is called the benzene ring. The term Bronsted - Lowry Acids - Bases The basic “aromatic” is derived from the sweet scent many of concept of this theory is that when an acid and these compounds have. a base react with each other, the acid forms its Arrhenius Acids are substances that when conjugate base and the base forms its conjugate added to water increases the concentration of H1+ acid by exchange of a proton (the hydrogen ions present. An example would be HCL. cation, or H+).

Arrhenius Bases are substances that when CAD/CAM System is the acronym for added to water increases the concentration of computer-aided design/computer-aided OH1- ions present. NaOH is an example of an manufacturing systems. They are used to design Arrhenius base. and manufacture products. An engineer can use the system to both design a product and program the machine that makes the part.

Capillary Action, sometimes called wicking or capillarity, is a manifestation of surface tension by which the portion of the surface of a liquid coming in contact with a solid is elevated or depressed, depending on the adhesive or cohesive properties of the material. A liquid may flow into narrow spaces without the assistance of gravity and indeed sometimes in opposition to it. An example would be a paintbrush in paint.

Carbocation is an ion with at least one positively charged carbon atom, for example methanium CH+. Benzene Rings are hexagonal rings arrangement found in benzene and other aromatic Charpy Impact Test or Charpy-notch test compounds, consisting of six carbon atoms with is a test that determines the amount of energy alternating single and double bonds between absorbed by a substance during fracture. The them, and with each carbon atom bonded to a energy absorbed is a measure of the material’s hydrogen atom, or to other atoms or groups of notch toughness. The Charpy impact test involves atoms in derivatives of benzene. striking a standard notched specimen with a controlled weight pendulum swung from a specific height.

3 COPYRIGHT©2016 CRAFTECH INDUSTRIES Chlorinated Polyvinyl Chloride (CPVC) Crazing refers to small hair-like cracks on the is a thermoplastic produced by the chlorination of surface of a plastic part. polyvinyl chloride (PVC) resin. Creep is the tendency of a solid material Coefficient of Linear Thermal to stretch or deform permanently under the Expansion (CLTE) is the relationship between influence of an unchanging load. a material’s dimensional response to heating and Cryogenics is the study of the production and cooling. behavior of materials at very low temperatures Comparative Tracking Index (CTI) that are generally accepted to be -150°C (-238°F). measures the electrical breakdown on the surface NIST has chosen to define cryogenics as below of an insulating material. It is often used to assess -180°C (-292°F). the electrical safety of an apparatus.

Compressive strength is the ability of a material to resist a compressive force and is the force per unit area that it can withstand. ASTM D695 is the standard test method used in the United States.

Condensation Polymers are any kind of polymer formed through a condensation reaction. With a condensation polymer, molecules join together and lose small molecules such as water or methanol.

Conductive Plastics are hybrid polymers that Crystalline polymers have a regular and are electrically conductive or static dissipative. defined pattern to their molecular structure. These plastics are engineered to have specific They have a melting temperature but not a glass conductivity characteristics using additives such as transition temperature. Polymers with regular copper, silver, aluminum, carbon black, and carbon chain structures (e.g. isotactic) are the most likely fibers. to form crystalline regions. The more crystalline a polymer is, the stronger and less flexible it Conductivity is the measure of how easily an becomes. electric charge or heat can pass through a material. Cut-off burs are a projection of material left Continuous Service Temperature is the when the work piece falls from the stock before maximum temperature at which a material can the edge has been broken. perform reliably in a long term application. CPVC See Chlorinated Polyvinyl Chloride. Copolymers are polymers of two or more different monomers. Deflection is the displacement of a material under load. It is expressed in inches or millimeters. Copolymerization is a process in which unlike molecules join together in random sequences Density is defined as the mass per unit volume or alternating sequences. An example of or ρ = m/v copolymerization is ABS plastic.

4 COPYRIGHT©2016 CRAFTECH INDUSTRIES Dielectric Constant is the relative permittivity Electromagnetic interference (EMI) is an of a dielectric material. electromagnetic energy that causes interference in the operation of electronic equipment by Dielectric breakdown is the point at which disrupting electrical circuits. conducting paths begin to form in an insulating material allowing electrical current to flow. Electrostatic discharge (ESD) is a sudden flow of electricity between two points such as the Dies are a specialized tools used in discharge of static electricity to the ground. manufacturing to cut or shape material mostly using a press. Dies are generally customized to the Elastic is a colloquial term for certain kinds item they are used to create. of elastomers. Elastic materials are capable of recovering their size and shape after deformation. Die Cutting is the process of using a die to cut low-strength materials, such as plastics, Elasticity is the physical property of a polymer rubber, cloth, paper, corrugated fiberboard, and that allows it to return to its original state after paperboard. deformation.

Elastomers are amorphous polymers existing above their glass transition temperature. At ambient temperatures, rubbers are thus relatively soft and deformable. Their primary uses are for seals, molded flexible parts, etc.

Fisch is a thermo softening plastic. Flame Rating/UL 94 is an internationally accepted plastic flammability testing standard created by Underwriters Laboratories. V stands for vertical flame and HB for horizontal burn. Expressed as V-0, V-1, and V-2. V-0 is a vertical burn that stops within 10 seconds. V-1 is a vertical burn that stops in 30 seconds and V-2 is one in which Dielectric Strength is the maximum electrical the vertical specimen stops burning in 30 seconds field strength a material can withstand without with the allowance of drips of flaming particles. HB experiencing failure of its insulating properties. is the designation for horizontal slow burn.

Dissipation Factor is the measurement Flame retardant materials are able to resist of how inefficient an insulating material is. It ignition when exposed to a flame or heat. measures the heat lost when an insulator such as a dielectric is exposed to an electrical field. Flavobacterium SP K172 is known as the nylon-eating bacteria and is a strain of ECTFE See Halar®. Flavobacterium that is capable of digesting certain Electrical strength is the maximum voltage by-products of nylon 6 manufacture. The enzymes a material can sustain before it loses its insulating used to digest the man-made molecules became properties. collectively known as nylonase.

5 COPYRIGHT©2016 CRAFTECH INDUSTRIES Flexural Modulus is a measure of how a plastic Homopolymer is a polymer composed of will deform and strain when weight or load is identical monomeric units. applied. It is calculated as the ratio of the initial Hydrocarbons in organic chemistry are organic stress to creep strain after a specific time under a compounds consisting entirely specific load. of hydrogen and carbon. The majority of Flexural Strength is the ability of a material to hydrocarbons found on Earth naturally occur resist deformation under load. in crude oil.

G-10-FR4 FR-4 is a glass-reinforced epoxy laminate sheets, tubes, rods and printed circuit boards (PCB). FR-4 is a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant (UL94VO self- extinguishing). G-10 is the non-self-extinguishing grade. Glass Transition Temperature (Tg) is the temperature below which a polymer becomes hard and brittle. This temperature is different for different plastics and does not apply to crystalline polymers. The transition is not itself a phase transition of any kind but rather is a Hydrolytic Stability is the ability of additives laboratory phenomenon extending over a range and certain synthetic lubricants to resist chemical of temperature. decomposition (hydrolysis) in the presence of Glow Wire Ignition Temperature (GWIT) water. is 25°K higher than the maximum temperature Impact-modified polymers are polymeric of the tip of a glow-wire which does not cause materials whose impact resistance and toughness ignition of a test specimen of a given thickness in a have been increased by the incorporation of phase maximum allowed time of five seconds. micro-domains of a rubbery material.

Halar® or ECTFE (Ethylene Instrumented Dart Impact is the energy ChloroTriFluoroEthylene) provides excellent required to puncture a material with the impact of chemical resistance in heavy duty corrosion a falling instrumented dart. ASTM D3763. applications. It is a partially fluorinated polymer (a fluoropolymer) and is semi-crystalline. Izod Impact Strength (Notched) To Chemically it is a copolymer of ethylene and determine the Izod impact strength, a swinging chlorotrifluoroethylene. pendulum with constant initial potential energy impacts a test specimen and breaks it. Heat Deflection Temperature or heat The specimen is usually notched to prevent distortion temperature (HDT) is the deformation on impact. The energy absorbed by temperature at which a polymer deforms under a the specimen is then equal to the energy lost by specified load. the pendulum. This measure is used to determine the impact strength of the material.

6 COPYRIGHT©2016 CRAFTECH INDUSTRIES Mass Spectrometry (MS) is an analytical Monocyclic is the term referring to polymers chemistry technique that helps identify the having one ring in the molecular cycle. amount and type of chemicals present in a plastic Monomer is a repeating molecular structure material by measuring the mass-to-charge ratio within a polymer. Monomers bond together to and abundance of gas-phase ions. form polymers by a process called polymerization Maximum Service Temperature is the in which the molecules are linked together by maximum acceptable temperature above which sharing electrons in a covalent bond. mechanical properties (tensile strength, impact Moisture Absorption refers to the capacity of strength) or electrical properties (dielectric a plastic to absorb moisture from the environment. strength, linked to insulation properties) of a The amount of moisture absorption depends on plastic part are significantly degrading, over the the kind of plastic used and on ambient conditions reasonable lifetime of the tested product. such as temperature, humidity and length of Melting Point is the transition temperature in contact. crystalline polymers at which the polymer chains NEMA is the acronym for the National Electrical fall out of their crystalline structure and become Manufacturers Association. See their website at liquid. www.nema.org. Mer Units are the unit of measure of the Nylon was first developed in the late 1930’s as a repeating structural unit of any polymer. One replacement for silk during World War II, when silk monomer is equal to one mer. Two monomers are became scarce in the US. Most nylons are made a dimer, three monomers are a trimer and so on. A from the reaction of a dicarboxylic acid with a polymer is many mers. diamine, as in Nylon 66, or a lactam or amino acid Molecular Weight is the mass of one mole with itself as in Nylon 6. Other grades include of a substance. Usually, the units used for this are Nylon 4/6 and Nylon 610. grams per mole. Ohms/Square Unit measures the surface Molding Shrinkage is the amount a plastic resistivity of a given material per a given unit of will shrink after the molding process. As different measure such as ohms/square inch, ohms/square plastics shrink at different rates, mold shrinkage centimeter or ohms/square meter. A lower ohms/ rates must be considered to ensure the product is square unit value indicates lower resistivity and dimensionally correct. better conductivity.

Oxidization/Oxidize is to combine with oxygen as with silver, which turns dark when reposed to oxygen.

Oxygen Index is the minimum concentration of oxygen in an oxygen/nitrogen mixture that will support a burning flame in a plastic specimen.

PA See Nylon.

PAI See polyamide-imide.

PEI See polyetherimide.

Perfluoroalkoxy alkane (PFAs) are fluoropolymers with properties similar to polytetrafluoroethylene (PTFE) prepared polytetrafluoroethylene perfluoro methylvinylether.

PEEK See poly ether ether ketone., with a different ratio of PTFE and MVE monomers from PFA, is MFA. In these materials, the ether groups are pendant from the polymer backbone.

Permittivity is the ability of a material to transmit (or permit) an electrical field. Also it is Polycarbonate (PC) is one in a group of a measure of the ability of a polymer to resist thermoplastic polymers containing carbonate formation of an electrical field within it. It is groups in their chemical structures. The express as a ratio of its electrical displacement characteristics of polycarbonate compare to to the applied field strength and is measured in those of acrylic, but polycarbonate is stronger farads/meter. and will hold up longer to extreme temperature. Polycarbonate is highly transparent to visible light, PES See polyethersulfone. with better light transmission than many kinds PFA See perfluoroalkoxy alkanes. of glass. Polycarbonates used in engineering are strong, durable materials. Although polycarbonate PP See polypropylene. has high impact-resistance, it has low scratch- Poisson Burrs are a result of the tendency resistance. Polycarbonate has a glass transition [7] of a material to bulge at the sides when it is temperature of about 147 °C (297 °F), so it softens compressed until permanent plastic deformation gradually above this point and flows above about occurs. 155 °C (311 °F).

Polyamide-imides can be either PolyChloroTriFluoroEthylene is a thermosetting or thermoplastic, amorphous fluorocarbon-based polymer and is commonly polymers. They are known to have exceptional abbreviated PCTFE. The Kel-F® brand is a mechanical, thermal and chemical resistant registered trademark of 3M, but they discontinued properties. Polyamide-imides display a production in 1995. The only remaining brand, combination of properties from both polyamides Neoflon®, is made by Daikin Industries of Japan. and polyimides, such as high strength, melt This OCTFE resin has the same chemical structure processibility, exceptional high heat tolerance, and and properties as the original Kel-F® brand broad resistance to chemicals. material. PCFTE offers the unique combination of physical and mechanical properties, non- Polyarylamide is a type of thermoplastic flammability, chemical resistance, near zero polymer able to accept a high filler loading and moisture absorption, and excellent electrical still have a resin rich surface. properties. These characteristics cannot be found

8 COPYRIGHT©2016 CRAFTECH INDUSTRIES in any other thermoplastic fluoropolymer with a Polyetherimide is an amorphous, amber-to- useful temperature of -400°F to +400°F (-240°Cto transparent thermoplastic material. +204°C). PCTFE also has extremely low out gassing Polyethersulfone (PES) is a polymer in a (0.01% TML, 0.00% CVCM, ) when tested per ASTM class of specially engineered thermoplastics. PES E-959-90, so it is suitable for use in aerospace and has high thermal, oxidative, hydrolytic stability, flight applications. and good resistance to oil and greases, aqueous Polycyclic describes a material that contains mineral acids, alkalis and salt solutions. two or more sets of close ring atoms. Polyphenylene Ether (PPE) is a thermoplastic, noncrystalline polyether. Polyphenylene ether is usually blended with polystyrene to improve its toughness and processability. Polyphenylene ether has excellent electrical properties, unusual resistance to acids and bases. PPE is attacked by some hydrocarbons, although it resists many other chemicals. Polyphenylene ether possesses low moisture absorption, excellent dimensional stability, and high mechanical and dielectric strength.

Polyphenylsulfone (PPSU) is a type PEEK is an abbreviation for PolyEtherEther- of thermoplastic plastic belonging to the Ketone, a high performance engineering polyarysulfone group of materials. It is a heat thermoplastic. PEEK can be used continuously to and chemical-resistant material typically used in 480°F (250°C) and in hot water or steam without automotive, aerospace and plumbing applications. permanent loss in physical properties. Known for It has high strength and stability even at elevated its performance in hostile environments, PEEK is a temperatures as well as being a chemically high strength alternative to fluoropolymers. PEEK resistant material. Polyphenylsulfone has virtually carries a V-O flammability rating and exhibits very no melting point due to its amorphous nature. low smoke and toxic gas emission when exposed Polyols are an alcohol containing multiple to flame. Unfilled PEEK is approved by the FDA hydroxyl groups. for food contact applications (since 1998). PEEK is commonly used in a wide range of industries and Polyphenylene Sulfide (PPS) is a applications from semiconductor to automotive crystalline polymer. Polyphenylene sulfides exhibit and aerospace. outstanding chemical resistance, thermal stability, dimensionally stability, and fire resistance. Permittivity is the ability of a material to transmit (or permit) an electrical field. Also, it is Polypropylene is a thermoplastic addition a measure of the ability of a polymer to resist polymer made from the propylene monomer. the formation of an electrical field within it. It is It is a tough plastic that is usually resistant to expressed as a ratio of its electrical displacement many chemical solvents, bases and acids. It is to the applied field strength and is measured in widely used in textiles, carpets, plastic parts, and farads/meter. laboratory equipment.

9 COPYRIGHT©2016 CRAFTECH INDUSTRIES Polysulfones are thermoplastic polymers. Radio Frequency Interference (RFI) is These polymers are known for their toughness and the radiation or conduction of radio frequency stability at high temperatures. Polysulfone has one energy or electronic noise produced by electrical of the highest continuous service temperatures and electronic devices at levels that interfere with among all melt-processable thermoplastics. the operation of adjacent equipment. Frequency Its resistance to high temperatures makes it a ranges of most concern are at 10 kHz to 30 MHz flame retardant plastic, without compromise of (conducted) and 30 MHz to 1 GHz (radiated) strength that can result from the addition of flame REACH is the anachronism for Registration, retardants additives. Its high hydrolysis stability Evaluation, Authorisation and Restriction of allows it to be used in medical applications Chemicals (REACH). It is a European Union requiring autoclave and steam sterilization. regulation passed in 2006. REACH addresses the Polytetrafluoroethylene (PTFE) is a production and use of chemical substances, and synthetic fluoropolymer of tetrafluoroethylene. their potential impacts on both human health and PTFE is a fluorocarbon and is a white solid at the environment. room temperature. It is a high-molecular-weight compound consisting wholly of carbon and fluorine. PTFE is hydrophobic that is neither water nor water-containing substances wet PTFE. PTFE has one of the lowest coefficients of friction any solid. The strong carbon-fluorine bonds make it nonreactive so it is used in applications for reactive and corrosive chemicals. It is also used as a lubricant as it reduces friction and wear as well as a nonstick coating for pans and other cookware.

PPE See polyphenylene ether

PPS See polyphenylene sulfide.

PPSU See polyphenylsulfone.

PSU See polysulfone. Resistance is the ability of a material to oppose PSI (pounds per square inch) is a unit of the flow of an electrical current. It is the reciprocal measure for pressure. It is the pound force per of conductance. square inch. Resistivity is the capacity of a specific material PTFE See Teflon. to resist an electrical current. It is the converse of conductivity. PVC See polyvinylchloride. Rockwell Hardness refers to a method of PVDF See polyvinylidene fluoride. testing the hardness of materials. Hardness in this case is defined as the resistance of a polymer to penetration. The Rockwell scales are the most recognized tests for hardness.

10 COPYRIGHT©2016 CRAFTECH INDUSTRIES RoHS is the abbreviation for the Restriction of Specific Gravity (Relative Density) is the Hazardous Substances Directive 2002/95/EC, short ratio of the mass of a substance to the mass of an for the Directive on the Restriction of the use of equal volume of water at 4° C (39° F) under given Certain Hazardous Substances in Electrical and conditions of heat and pressure. Electronic Equipment. It was adopted in February SPE is the acronym for the Society of Plastic 2003 by the European Union. Engineers. Visit their website here www.4spe.org.

Stress cracks are internal or external cracks in a solid plastic body caused by tensile compressive or shear force.

Surface Resistivity is the ratio of DC voltage to the current that passes across the surface of a substrate. The unit of measure is ohms/sq. and is an indication of how conductive a material is.

Tear Burrs are the result of material tearing loose from the work piece rather than shearing it.

Tear Resistance is calculated by dividing the force applied by the thickness of the material.

A Rollover Burr is essentially a chip that is bent Ter Polymers are a resin that results from rather than sheared and results in a comparatively copolymerization of three discrete monomers. larger burr. This type of burr is also known as an Tensile Strain at Break or Ultimate exit burr because it is usually formed at the end of Tensile Strength (UTS) refers to the a cut. maximum stress a polymer can withstand while Self-extinguishing is a term somewhat loosely being pulled or stretched without breaking. applied to describe the ability of a polymer to Stress=force/area or F/A. It is expressed in MPA (Sl stop burning after a flame applied to it has been units) or PSI (KSI Units) removed. Tensile Strength Modulus is defined as Semi-crystalline polymers contain both strain=extension/length or ΔL/L. It is the ratio crystalline regions called crystallites within an of the uniaxial stress over the uniaxial strain in a amorphous matrix. This kind of polymer forms the polymer. It is determined by the slope of a stress/ largest group of commercially used polymers. strain curve. There is no unit of measure as it is a simple ratio. Shore Hardness is a measure of the hardness of a material obtained by pressing a needle into TEFLON (PTFE) See Polytetrafluoroethylene. a test specimen and determining how deep it penetrates. Shore A is defined as the measurement using a blunt tip needle and Shore D as the measurement taken using a needle with a 30 ° point angle. The higher the value, the greater the hardness.

11 COPYRIGHT©2016 CRAFTECH INDUSTRIES Thermoplastics are plastic materials that Unlike most plastics, it does not produce become moldable above a specific temperature significant outgassing even at high temperatures. and solidify upon cooling. Most thermoplastics It performs well in vacuum applications, down to have a high molecular weight. The polymer chains extremely low cryogenic temperatures. Although associate through intermolecular forces, which there are polymers that surpass Vespel® in weaken rapidly with increased temperature, individual in properties, it is the combination of yielding a viscous liquid. Thermoplastics may them is the main advantage of Vespel. be reshaped by heating and are typically Vicat Softening Temperature is used to used to produce parts by various polymer determine the softening point for materials that processing techniques such as injection molding, have no definite melting point. The temperature at compression molding, and extrusion. which a flat-ended needle penetrates a specimen Thermal Conductivity in physics (often to the depth of 1mm under a specific load. ASTM denoted k, λ, or κ) is the property of a material D 1525. to conduct heat. It is evaluated primarily in terms of Fourier’s Law for heat conduction. The reciprocal of thermal conductivity is called thermal resistivity or ‘R’.

Thermoset plastics do not melt, but decompose and do not reform upon cooling.

Toxic Substance Control Act (TSCA) is a United States law passed in 1976 and administered by the United States Environmental Protection Agency that regulates the introduction of new or already existing chemicals. The TSCA specifically regulates polychlorinated biphenyl (PCB) products.

TPU See thermoplastic polyurethane.

UHMW-PE See high molecular weight Viscoelastic materials have both elastic and polyethylene viscous properties like plastics. UL is the acronym for Underwriters Laboratory. Volume Resistivity is a measure of an object’s Visit their website here www.ul.com. ability to carry an electrical current through the Ultimate Elongation refers to the elongation bulk of a material. The unit of measure if ohm-cm. of a polymer sample at break. Young’s Modulus is a numerical constant that Vespel® is the trademark for a durable high- describes the elastic properties of a solid under performance polyimide-based plastic. Vespel® tension or compression from only one direction. It is commonly used in aerospace, semiconductor is a measure of stiffness. and transportation applications. It combines Wavelength refers to the distance between one outstanding heat resistance, lubricity, dimensional amplitude and the next of an electrical current or stability, chemical resistance, and creep resistance. the distance over which the wave shape repeats.