## 4. Constructional and Functional Aspects of Chains
### Requirements and Dimensioning  
In the context of technical link chains, standards and guidelines play a critical role in ensuring reliability, safety, and proper functionality. For instance, ISO 3076 [71] defines dimensional tolerances and mechanical property requirements for industrial and transport chain systems. This standard outlines geometric parameters such as nominal link length, bar diameter, and curvature radii, which directly affect stress distribution during operation. At the final stage of design, optimization is performed with respect to cost, mass, and manufacturing requirements to produce durable and reliable chains for various applications. The geometry of these often single structural elements--combined into a continuous assembly--and the selection of suitable materials significantly influence the strength, stability, and longevity of the entire connection system. With the dynamic advancement of material science, particularly in the field of fiber-reinforced polymer composites, it has become possible to achieve improved strength characteristics while simultaneously optimizing production processes. Strength calculations account for maximum loads and include stress and strain analysis, often supported by the finite element method (FEM). Prototypes are subjected to tensile and fatigue testing. Heattreatment processes for metallic chains, such as hardening and nitriding, improve both mechanical properties and corrosion resistance [72; 73]. Standard requirements also include classification of chains according to load capacity, which depends on their resistance to static and dynamic loads. For example, EN 818 [74], which applies to steel chains, defines strength classes such as G80, G100, and G120\(-\)with each subsequent class offering increased load capacity relative to the chain's self-weight. This classification facilitates the appropriate selection of chains based on working load and operating conditions. Technical evaluation is another essential component of chain design and assessment. Standards such as ISO 1834 [75] and ASTM A0391 [76] specify testing methods, including tensile, fatigue, and wear resistance tests. These procedures verify the strength of individual links under multidirectional forces and assess durability under variable loading conditions. Figure 6 illustrates the geometric characteristics of a metal link in a technical chain, including the link length (L), width (B), bar diameter (d), and internal length (t). These parameters are essential for dimensional consistency and proper alignment of links within the chain. In this example, the chain conforms to DIN 5685 C [77]. Adherence to normative dimensional guidelines ensures uniform force distribution and minimizes the risk of mechanical failure. The requirements and dimensioning of chains are regulated by various international, European, and national standards, depending on the type of chain, its application, and the industry in which it is used. A large number of currently applicable standards exist. Based on publicly available information [78; 79; 80; 81; 82], Table 3 presents a compilation of the most widely used European and American standards. It is important to note that no dedicated standards currently exist for the design and manufacture of composite or polymer chains. \begin{table}
\begin{tabular}{c c l} \hline
**Standard** & **Number** & **Title** \\ \hline ISO & 610:1990 & High-tensile steel chains (round link) for chain conveyors and coal plows [83] \\ ISO & 1834:1999 & Short link chain for lifting purposes\(-\)General conditions of acceptance [84] \\ ISO & 1835:2018 & Round steel short link chains for lifting purposes\(-\)Medium tolerance sling \\  & \(-\)Grade 4, stainless steel [85] \\ ISO & 3076:2012 & Round steel short link chains for general lifting purposes\(-\)Medium tolerance sling \\  & \(-\)Grade 8 [86] \\ DIN & 762-2 & Quenched and tempered grade 5, round steel link chains [87] \\ \hline \end{tabular}
\end{table} 
Table 3: List of examples of currently applicable standards for link chains.