For plastics, textiles, and wood, the reaction of materials toward temperature, humidity, and mechanical stress defines their dimensional stability which is one of their fundamental properties. This concept ensures that materials across various applications have performance, durability, and reliability. This article sets out to inform engineers, designers, and other professionals in the field of materials science about the causes of dimensional stability, its measurement, and enhancement techniques. These principles, when mastered, assist in the discretion of materials required and affect their optimization in industrial and day-to-day activities.
What is Dimensional Stability and Why is Important to Us?
The term “dimensional stability” is described as a material’s ability to retain its shape and size when exposed to certain temperature, humidity, or mechanical force changes. It is crucial since otherwise strain-controlled applications may result in ou t-of-round conditions, malfunctioning, destructive fracturing, or catastrophic failure in extreme cases. As for the construction, automotive, or aerospace industry, negligence in particular areas can lead to a dimensional stability failure which can, cause severe damage to trim, affect longevity, and many other outcomes.
How Does It Change Divisions Occured
The material causes to dimensional change are moisture tightening, thermal expansion, and mechanical stress.
The term “dimensional stability” is described as a material’s ability to retain its shape and size when exposed to certain temperature, humidity, or mechanical force changes. One of the ways a material may change due to heating is expanding. As an example, steel is known to have an average thermal expansion at a rate of 11.7 x10⁻⁶/°C, including aluminum, which has a higher average rate of 23.1 x10⁻⁶/°C. These numbers are result from applying a temperature-change ratio to accomplishment of two different segments with steel as a base. Alternative thermal expansion exhibits behavior that can be expected with other metals or materials.Examples of hygroscopic materials include wood and certain polymers. These materials can absorb moisture, resulting in swelling or dimensional changes. For instance, while in high-humidity conditions, nylon can absorb up to 7% of its weight, resulting in a 2-3% dimensional increase. Such effects in sensitive applications need proper sealing or stabilizing methods to control these issues.
Prolonged exposure to some amount of mechanical stress may also cause the material to deform over time due to creep. This is of particular concern in high-temperature settings, such as with turbine engines. For example, at 600°C, stainless steel can creep at rates that need careful consideration during design for expected lifespan load bearing capability.
Meeting the requirements in the application of the material are ensuring factors like accurate modeling, selection of the appropriate material, and sufficient testing are managing and understanding the factors throughout the lifecycle of the material.
Why is Dimensional Stability Critical in Textile Products
Dimensional stability is critical in textile products because it helps materials to maintain their size, shape, and fit over the course of their life. This internal characteristic of textile materials directly determines its value, quality, performance, and the satisfaction level of the consumer. Factors such as fiber type, yarn structure, weaving or knitting methods, and finishing treatments affect the dimensional stability of textiles. For instance, untreated natural fibers such as cotton tend to shrink more during washing than other types of fabrics, and untreated synthetic fibers tend to have higher stability in size over a range of conditions. To improve stability and correct problems related to shrinkage or stretching, more advanced methods of fabric finishing like heat setting or chemical treatments are used. In technical textiles designed for precision applications like sportswear or medical textiles, where optimal fit and performance is critically required, while maintaining dimensional stability, are other areas where dimensional stability is emphasized.
Role of Dimensional Stability in Engineering Plastics
There are a number of factors that dictate the ability of engineering plastics to retain their shape, size, and proportions over a range of temperatures, pressures, and other types of environmental and mechanical conditions. Some of these factors are discussed below.
- Plastics exhibiting greater thermal expansion coefficients are less stable as they are more likely to change volume (expand or contract) with temperature.
- Hygroscopic materials absorb moisture from the environment. Examples are polyamides (nylons) which with time lead to geometric change.
- The glass transition temperature marks the value at which one measures plastic materials changing from a rigid state to more rubbery and bendable state, which also affects stability.
- Additives Glass Fibers or carbon have been shown to enhance the plastic’s dimensional stability by lowering the plastic’s thermal expansion and increasing the stiffness of the material which is more rigid.
- Plastics are subjected to various processes like cooling, molding, and annealing which induce certain internal stress that affects the long-term stability of the dimensions of the plastic.
- Residual stresses that are set during manufacturing usually causes unstable conditions in the finished piece as the workpiece automatically contorts during the inactivity period and therefore distorts the workpiece changing its stability.
- Plastics undergoing sudden breaching of the UV protective layer covering the plastic object and exposing it sudden bending moments and temperature can severely deform these materials, constantly altering them over time
- Steady application of external forces on an object for a long time results in creep which in turn is progressive deformation máquinas like turning or grinding the solid.
- Like PEEK and PPS, high-performance thermoplastics, and other engineering plastics with more uniform molecular structures, typically have better dimensional stability.
By taking these factors into consideration, manufacturers can tailor the design and processing strategies of the required engineering plastics to meet the desired stability criteria specifically tailored for a given application.
How Do Various Factors Affect Dimensional Stability?
Moisture Absorption Considerations and its Impact on Relative Humidity
The absorption of moisture swells nylon (polyamide) which is highly hygroscopic and it affects the engineering plastics moisture greatly. Water molecules disrupt the structure of a polymer, which increases the polymer size. For example, under 100% relative humidity conditions, nylon tends to absorb up to 8-9% of its weight, which for some polymers, can also result in volumetric increase or swelling of up to 2-3%.
The variation can be even upto 100% as described above in gears or biological components where precision is crucial and takes a big hit towards the value. In one such study, it was found that under 50% relative humidity, the nylon 6 parts showed a volumetric change of approx 1% but at 75% they change the volumetric change to more then 1.7%. This shows why consideration of harsh and tough selective guides are paramount during the design and construction of complex systems that require robust materials.
By doing so, the outcome becomes more desirable so many designers add fiberglass reinforcements to lower the moisture absorption rate or use acetal (POM) polymers which water isuth0less than 0.25% under those conditions. These trends ensure the quality use of the technology of polymers in complex environmental conditions.
Effects of Thermal Expansion and High Temperature
High temperatures affect the mechanical properties and the dimensional stability of plastics thermally and through expansion. Different materials have different compositions and structures which impact the range CTE (coefficient of thermal expansion) is exhibited by thermoplastics. Most thermoplastics show a CTE between 50 to 300 μm/m/°C, while Polyethylene (PE) has a higher CTE of 200-250 μm/m/°C and Polycarbonate (PC) a lower one between 65-70 μm/m/°C. Thus, polycarbonate demonstrates a greater stability in dimensions under thermal stress.
Some plastics become susceptible to softening or losing vital mechanical properties at certain high temperatures:
– Polypropylene (PP): It starts softening approximately around 100°C with its melting point between 160-170°C.
– Nylon (PA): Displays a drop in tensile strength and stiffness past the glass transition temperature (~50-70 °C). Mist of nylon grades will melt within the range 220-265°C.
– Polyetheretherketone (PEEK): Shows exceptional capabilities in enduring high temperatures, controlling structural integrity up to ~250°C under continuous use state.
PEEK is a heat resistant polymer which protects materials that undergo significant stress for long periods of time. Adding thermal-stabilizing fillers and switching to heat resistant polymers also provide similar benefits by preventing changes in shape and properties.
The Effect of Mechanical Stress alongside Internal Stress
Considered from any perspective, mechanical stress due to either external factors or internal processes originates the impact the stress will have on polymers and their useable lifetime is crucial. External forces of straight mechanical strain, elongation, and compression may result in structural damage in the form of deformation, cracking, or disintegration depending on the polymer’s strength and elasticity. Considerable internal stress, which is assumed to occur during the processes of molding, cooling, or machining, can result in gradual fatigue by fissuring material under constant strain and use.
To mitigate these effects, polymers that are more resistant to structural change, or further stabilizers such as fiber glass or carbon also improve withstandability. Also, internal strain can be a resolvable issue with the right thermal treatment alongside deform and relax techniques enabling better performance and stability. Attending to internal decisional stress fractures improves the reliability and defensibility of the system which ensures consistent stability tension performance while modular computations increase scale integration. Proper internal decisional fracture computation ensures the reliability of the architecture even under realistic operating conditions.
What are the Types of Shrinkage in Materials?
Explaining Fabric Property Shrinkage and Dimensional Stability
Shrinkage of a material can occur due to a number of reasons. These reasons usually depend on the makeup of the material, environmental conditions, and the ways it underwent processing. It is important to know the these differences when working with materials and ensuring their stability and functionality while meeting operational requirements. Here is a description of different types of unique classification systems:
- Defined as a reduction in dimensions and is caused by exposure to temperature change, particularly cooling events subsequent to heating or thermal exposure.
- Tracking along the lines of the definition, this phenomenon is also observed in metals and polymers since they also shrink when subjected to lower temperatures.
- As a result of a thermal measuring process done with a coefficient of thermal expansion (CTE), this can be quantified.
- Change in volume owing to moisture loss or moisture gain for materials that absorb moisture, particularly wood, paper and certain textiles.
- In large parts, this alters the state of humidity of the surroundings.
- Measured through percentage figure criteria such as moisture regain and moisture content.
- Captures materials such as concrete and the changes that occur due to evaporative processes that occur during the curing phase.
- Leads to the development of micro cracks associated with a volume decrease. further leads to volumetric strain which induces structural stress.
- This is achievable by controlling the methods administered to the curing procedure.
- This can be achieved in other processes that use polymerization such cement hydration reactions.
- In normal circumstances, we expect that there is a reduction in volume as a material undergo changes with its molecular makeup.
- This is observable when the load that’s been exercised is released.
- Described as the property of elastomeric and viscoelastic materials, recoverable upon removal of external force: deformation.
- This deformation does result in, although minimal, a change in dimensions.
- Outcomes from manufacturing processes such as injection molding or casting, in which liquid substances undergo cooling and solidification.
Considerable shrinks requires tolerances to be set at the time of production.
In What Manner Does Shrinkage impact Plastic Materials
This form of shrinkage is caused by a number of factors that focus on accuracy abstraction as well as the final measurements of different dimensions and overall weight of the product.
The underlined factors along with their corresponding data have been provided.
Shielding structures as well as fillers which make up the plastic play a major role in shrinkage.
Other examples include:
Crystalline Polymers (e.g., polypropylene, polyethylene): Sustains level of shrinkage ranging from 1.5% to 3.0% (High Shrinkage).
Amorphous Polymers (e.g., polystyrene, polycarbonate): Regarded at a range of 0.3% and 0.8%, hence low.
Reinforced plastics, like those which comprise shard glass, can go as low as 0.1% shrinkage due to inferior molecular contraction.
Besides results that are lower, elevated temperatures within the mold greatly improve the overall flow of the material, resulting in more shrinkage. For instance:
0.1% to 0.3% based on what type of polymer, 20°C increase within the mold can raise shrinkage.
Rapid cooling usually leads to a lower amount of shrinkage but can cause internal stress, which may compromise the durability of the part:
Uniform shrinkage is more easily achieved with slow cooling but can result in an increase in overall percentage.
Regions with greater thickness have longer cooling times, and therefore, higher localized shrinkage:
Some crystalline plastics are estimated to have a shrinkage of 4% or more resulting from wall thicknesses of 3mm or more.
What are the Test Methods for Ensuring Dimensional Stability?
ASTM and ISO Standard Test Methods Overview
The following steps describe the test methods established for measuring and ensuring material stability in length, width, thickness, and other directions:
Purpose: To measure the shrinkage of thermoplastic materials by measuring changes in dimensions after molding.
Key Data Measured: Shrinkage linear percentage of flow and cross flow directions.
Applications: Commonly employed in optimizing the injection molding process.
Purpose: To provide instructions on molding specimens for evaluating the shrinkage and other physical properties of thermoplastic materials.
Key Data Measured: Shrinkage values determined for certain thermoplastic materials based on geometry of molded parts.
Applications: Quality assurance in part production and material selection.
Purpose: To measure the shrinkage of thermoplastics in all directions after cooling under specified control conditions.
Key Data Measured: Values of shrinkage in millimeters or percentage of the original dimensions.
Applications: Comparing materials for the production of precision parts.
ASTM D648 – Standard Test Method for Deflection Temperature of Plastics Under Flexural Load
Purpose: To determine the heat resistance of constituents under concrete loading, contributing towards the assessment of the constituent’s stability analysis in dimension.
Key Data Measured: Deflection temperature for evaluating thermal performance.
Applications: Determining constituents in environments experiencing high temperatures.
Aim: Evaluate the linear thermal expansion and contraction behaviors of plastics.
Primary Information Evaluated: Thermal expansion/contraction coefficient (CTE) and dimensional changes relative to temperatures within a set range.
Other Uses: Assessment of thermal stability and design evaluation for systems sensitive to temperature changes.
ASTM E831 – Standard Test Method for Evaluation of Linear Thermal Expansion of Solid Materials
Aim: Measures solid materials expansion under a predetermined level of heat and over a determined time.
Primary Information Evaluated: Coefficient of linear thermal expansion.
Other Uses: Assessment of material precision for applications with specific dimensional accuracy requirements.
Aim: Evaluate heat deflection plasticity of materials by measuring how much plastic deforms under constant load over time and temperature.
Primary Information Evaluated: Deflection temperature under load (DTUL).
Other Uses: Application of heat-shrink resistant materials to parts that must endure heavy load.
How to Assess the Dimensional Change of Textiles
Measuring dimensional change in textiles necessitates taking into consideration a number of important metrics and parameters that ensure accuracy and reliability. To achieve optimal results, the accuracy of these data points should be as follows:
Calculation of shrinkage or expansion of the fabric’s width and length under exposure to certain conditions.
Evaluation of the weft wise dimensional changes that occur during the testing process.
Works out the total percentage increase in area of fabric by calculating the increase in both length and breadth.
Assess the fabric’s weight per unit area (gram per square meter) to determine the density changes after undergoing treatment to measure the change.
Provides a measurement of change relative to the bounds of the object which is used to express the dimensions as a percentage of original value in order to provide standard metrics.
Contains relevant information such as temperature, humidity, and time of exposure which are significant to the overall test results.
Significance of Quality Control in the Production of Textiles
For example, washing at 40°C, followed by drying at 60°C, shows the results for shrinkage measurement. Shrinkage measurement post laundering processes.
- Results shows that cottons and synthetic blends undergo dimensional changes of, respectively, up to 3% and 1.5% under standard condition.
- Under both wet and dry conditions with a tensile testing machine.
- Average tensile strength observed for is 30 N/mm² dry and 25 N/mm² wet for cotton samples.
- Assessed by 72 hours of exposure to artificial light followed by washing cycles.
- Measured fading rate ranges between ΔE equal to 1.2 up to 3.0 subject to dye composition and fiber type.
- Under identical test conditions, synthetic fabrics had an absorption rate of 5% in 30 seconds compared to 8% for cotton.
How Can Materials Be Made More Dimensionally Stable?
Ways to Enhance Dimensional Stability in Textile Products
Within 30 seconds, synthetic fabrics: 5% absorption.
Cotton fabrics: Total absorption of 8% in the same duration.
Observed range of tests: 1.2 to 3.0.
These variations are influenced by dye composition and fiber type.
Cotton textiles are known to shrink an average of 2.5% post the first wash.
Shrinkage is less for blends with polyester at about 0.8%.
Nylon that has undergone heat treatment shows an increase in length of 1.2% at 140°F (60°C).
Hy Un-Treated polyester maintains better stability at higher temperatures <1% elongation.
Elongation and stress are withstood more effectively by synthetic fibers, maintaining stability through 95% of stress load tests.
Under such conditions, deformation for natural fibers like wool are at 10-15%.
These points of data focus on the primary areas of improvement and reinforce efforts towards achieving dimensionally stable textile products.
Increasing the Dimensional Stability of Wood and Plastic Polymers
Effect on Change in Moisture Content: Solid wood is usually considered to be hygroscopic in nature, that is it shows 0.2% – 0.3% dimensional change in width and thickness for every 1% change in moisture content. So controlling humidity in storage and application environments will greatly reduce the risks of deformation.
Stability Under Temperature Stress: Solid wood displays some degree of thermal stability as well, showing approximately 2.5 – 3.5% of dimensional shrinkage when subjected to temperatures between 50 degrees celsius to 80 degrees celsius. Further exposing it to these limits tends to cause permanent irreversible damage to its structure.
Plastic Thermal Expansion: Depending on the type of polymer, plastic receive linear expansion coefficients between 50 x 10^-6 /°C to 200 x 10^-6 /°C. High performance plastics such as polyetheretherketone (PEEK) do maintain these margins but sustain closer to 50×10^-6/°C showing better performance than general-purpose polymers such as polyethylene.
Load Stress Resistance Evaluation: Studies conducted around 80% of the limit tensile stress exposed to show an average deformation around 0.8-1.2% indicating that plastics perform remarkably better and can withstand structural integrity even under more severe load conditions.
Frequently Asked Questions (FAQs)
Q: What does dimensional stability mean and what is its importance in materials such as plastics, textiles, and wood?
A: It’s the capacity of a material to preserve its original measurements under varying temperatures, humidity, or other environmental changes. This characteristic is important because if something has low dimmensional stability, it may warp, buckle or deform and this may have an impact on it’s functionality, use, and even looks.
Q: How is the fabric dimensional stability tested?
A: The fabric expects are put through a set of conditions like washing in a washing machine. This is expected to follow the relevant washing and drying protocols of the volume of water used which compares to the estimates associated with washing machines of various makes. Fabrics have to ephemeral dimension changes as set within a defined distance in order to meet qualitative benchmarks. The fabric dimensional stability tests are constructed to fail in a hard manner touch adhere fail failure modes. This AATCC test enables the achievement of high quality standards.
Q: What are dimensionally stable plastics and how are they used?
A: Dimensionally stable plastics are defined to be flexible structure bearing materials. They retain their shape and size under changes in temperature and at extreme ones too. Construction applications need these materials as do precision mechanic and robotics, and electronics where electrical properties become critical.
Q: In what ways does dimensional stability influence the manufacturing of textiles?
A: In the production of textiles, dimensional stability impacts the quality and longevity of the product. Fabrics with high-range enduring stability do not lose their shape or fit after wearing and washing it, which is essential for businesses in terms of customer satisfaction and lowering returns due to poor stability.
Q: What causes a lack of dimensional stability in wood?
A: In woodworking and construction projects, wood’s exposure to humidity and changes in moisture content and temperature may lead to warping or buckling, compromising its structural soundness and visual appeal.
Q: Are there specific tests used to gauge the stability of different materials in relation to dimensions and volume, such as textiles, plastics, or wood?
A: Yes, there are specific tests used to measure the dimensional stability of different materials, including textiles, plastics, and wood. These measures determine how materials balance with the environment, adjusting to changes within the surroundings concerning heat and moisture.
Q: What role does fibre composition play in the fabric’s structural alteration resistance?
A: Fibre composition plays a significant role in fabric dimensional stability. The presence of natural and synthetic fibres brings out a different set of features as they face some environmental factor. Knowledge on fibre composition assists greatly in choosing the materials with appropriate stability in size and shape alterations.
Q: Does the washing machine have an effect on the fabric’s ability to retain its shape or size?
A: Yes, washing machines can impact the dimensional stability of fabrics. The rotating action together with the water temperature of the wash cycle tends to shrink or stretch pieces of fabric, making the use of these tests for stability invaluable in construction for fabrics meant to endure laundering.
Q: How can the dimensional stability of a product be improved by the manufacturers?
A: The right materials need to be selected and appropriate tests for dimensional stability need to be conducted to optimize production processes. Environmental conditions during production need to be controlled, and treatments or coatings which enhance dimensional stability need to be employed, to enhance dimensional stability.
Reference Sources
- Title: Dimensional Stability and Accuracy of Silicone – Based Impression Materials Using Different Impression Techniques – A Literature Review
- Authors: B. Naumovski, B. Kapushevska
- Journal: PRILOZI
- Publication Date: September 1, 2017
- Citation Token: (Naumovski & Kapushevska, 2017, pp. 131–138)
- Summary: This literature review evaluates the dimensional stability and accuracy of various silicone impression materials and techniques. It highlights the importance of material choice and technique on the dimensional stability of impressions, emphasizing that addition silicone materials generally outperform condensation silicone materials in terms of stability.
- Title: The effect of prolonged storage and disinfection on the dimensional stability of 5 vinyl polyether silicone impression materials
- Authors: U. Nassar, C. Flores‐Mir, G. Heo, Y. Torrealba
- Journal: The Journal of Advanced Prosthodontics
- Publication Date: June 1, 2017
- Citation Token: (Nassar et al., 2017, pp. 182–187)
- Summary: This study investigates the dimensional stability of vinyl polyether silicone (VPES) impression materials after disinfection and storage. The results indicate that the materials maintained dimensional stability within acceptable limits after disinfection and up to two weeks of storage, suggesting their clinical viability.
- Title: Dimensional Stability of a Preliminary Vinyl Polysiloxane Impression Material
- Authors: F. Martins, J. Reis, Ignacio Barbero Navarro, P. Maurício
- Journal: Dental Journal
- Publication Date: August 1, 2019
- Citation Token: (Martins et al., 2019)
- Summary: This study evaluates the dimensional stability of a vinyl polysiloxane impression material over time. The findings indicate that the material exhibited minimal shrinkage over a week, confirming its suitability for clinical applications.
