Main external causes that create mechanical stress on paints coatings
Extreme Temperature Fluctuations
Extreme temperature fluctuations can have detrimental effects on paint coatings. When temperatures fluctuate significantly, the materials comprising the paint expand and contract at different rates. This differential expansion and contraction can lead to stress within the paint film, causing it to crack, peel, or even delaminate from the substrate over time. These cracks and separations provide pathways for moisture and contaminants to penetrate the paint, accelerating degradation processes such as corrosion or mold growth. Aditionally, apart from the thermal effect of temperature on the expansion and compression of metal, in extremely cold humid climates, water and moisture freeze and expand. If the coating traps this moisture, it would be exposed to tensile forces within. Moreover, repeated cycles of expansion and contraction can weaken the adhesion between the paint and the underlying surface, compromising the overall integrity and protective capabilities of the coating. If this is compounded by poor surface preparation (resulting in poor adhesion) along with extremely humid weather, the integrity and effectiveness of the paint could be severely compromised. Proper selection of paint formulations designed to withstand thermal cycling and adherence to recommended application practices are essential to mitigate these damaging effects of temperature fluctuations on painted surfaces.
Vibration & Physical Impact and Mechanical loads
Vibrations, mechanical loads, and physical impact pose significant threats to the integrity of paint coatings. Vibrations, stemming from industrial activities or natural events like seismic movements, can induce repetitive stresses that weaken the adhesion of the coating to the substrate, potentially causing cracks and detachment. Meanwhile, mechanical loads, including the weight of objects and movement of equipment on painted surfaces, can generate static or dynamic stresses that locally deform the coating, compromising its protective capability and increasing the risk of peeling or fracturing. Physical impact, resulting from direct collisions or blows, can lead to visible damage such as dents and chipping in the coating, exposing vulnerable areas to corrosion and accelerating deterioration. To mitigate these risks, it is essential to select coatings designed to withstand these specific forces and implement proper maintenance practices that include prompt repairs for any detected damage, thereby ensuring the durability and effective protection of painted surfaces.
Abrasion
Abrasion refers to the gradual wearing down of a coating's surface due to constant friction with rough objects or abrasive surfaces. This wear can be caused by everyday activities such as foot traffic, furniture or object rubbing, and repeated movement of equipment or machinery over the painted surface. Additionally, adverse environmental conditions such as the dragging of sand or dust particles can contribute to the abrasion process. Mechanical abrasion compromises the protective layer of paint, reducing its thickness and exposing the underlying surface to additional damage such as corrosion or degradation.
Internal Forces in Mechanical stressed paint coatings
Tensile Stress
Tensile stress is a type of stress that refers to the internal forces per unit area acting to stretch or elongate a material when an external force is applied that tends to pull it apart. Simply put, it is the force that tries to separate the particles of a material, causing it to lengthen
Tensile stress can be generated by several factors. One of the main causes is temperature fluctuation. When the temperature rises, materials tend to expand, and when it decreases, they contract. These variations can create tensile stresses in the paint if the substrate and the paint do not expand or contract at the same rate, potentially leading to cracking. Additionally, mechanical stresses applied during regular use, such as structural movements or vibrations, can also induce tensile stresses in the paint, especially in areas where the coating is stretched or subjected to forces that tend to separate its layers.
Compressive stress
Compression stress is a type of stress that refers to the internal forces per unit area acting to compress or reduce the volume of a material when an external force is applied that tends to push it together. In other words, it is the force that tries to shorten or crush the particles of a material, making it more compact.
In the case of paint coatings, compression stress can be generated by several factors. One of the main causes is direct physical impacts, such as blows or collisions, which apply a sudden force to the painted surface, generating localized compression stresses that can cause dents or paint delamination. Aditionally, mechanical loads, such as the weight of objects or equipment on the painted surface, can also induce compression stresses that deform the coating.
Shear Stress
Shear stress is a type of stress that refers to the internal forces per unit area acting to slide one layer of material over another in opposite directions. Simply put, it is the force that tries to make the particles of a material slide past each other, deforming the material in a plane parallel to the applied force.
In the case of paint coatings, shear stress can be generated by several factors. One of the main causes is differential movement between the substrate and the paint layer. This can occur when the substrate deforms due to mechanical loads or vibrations, and the paint cannot uniformly follow this deformation. Additionally, temperature fluctuations can cause differential expansion and contraction between the substrate and the paint, generating shear stresses at the interface between the two materials.
Another common cause of shear stress is the application of tangential forces on the painted surface, such as constant rubbing of objects or friction caused by repeated contact. This can happen on surfaces subjected to pedestrian or vehicular traffic, where continuous friction can induce shear stresses that eventually wear down or damage the coating.
Wind can also be a factor, especially in outdoor structures. Wind gusts can apply tangential forces to the surface of the paint, generating shear stresses that, if repetitive or strong enough, can cause delamination or cracking of the coating.
Bending Stress
Bending stress refers to the internal forces per unit area that develop within a material when subjected to bending moments or flexural loads. It occurs when a material experiences a combination of tensile and compressive stresses on opposite sides of its cross-section due to applied bending forces.
In the context of coating paints, bending stress can arise from structural deformations or movements. Structures such as beams, panels, or surfaces can bend under the influence of loads, wind, or thermal expansion. As these structural elements bend, the outer surface experiences tension on one side and compression on the opposite side. This differential stress distribution across the coated surface can lead to deformation or failure of the coating if it cannot accommodate the bending without cracking or delaminating.
Temperature variations also contribute to bending stress in coatings. Differential expansion and contraction between the substrate and the paint layer can induce bending moments on the surface. For instance, during temperature changes, if the substrate expands or contracts more than the paint, it can create bending stresses that affect the adhesion and integrity of the coating.
Additionally, improper design or installation of structural elements can lead to uneven distribution of bending forces, causing localized bending stresses on the coating. Over time, repeated or excessive bending stresses can weaken the coating system, resulting in cracks, fractures, or detachment from the substrate.
