Joint Separation Load
Calculate the external load that causes a bolted joint to separate (open), P_0 = F_i ÷ (1 − C), from the preload F_i (N) and the joint stiffness constant C. The separation load is the external tensile load at which the compression between the clamped parts fully vanishes — the point where the joint starts to OPEN. Below it, the parts stay compressed and the joint behaves 'smartly' (the bolt feels only C·P of the external load, with small stress variation); ABOVE it, the parts separate, and from then on ALL additional external load goes straight to the bolt (which then takes the whole load, with severe fatigue and failure risk). Joint separation is thus a condition the design must AVOID with margin: a safety factor against separation is applied (the separation load must be well above the maximum expected external load). The formula shows the separation load grows with preload (well-tightened joints separate later) — another reason to use high preloads. Separation also causes leaks (in sealed joints), loss of stiffness and loosening. Ensuring the joint never separates under service load is a fundamental bolted-joint design criterion. Enter the preload and the stiffness constant.
Resultado
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Carga de separação da junta
A carga de separação de uma junta aparafusada é P_0 = F_i ÷ (1 − C), a partir da pré-carga F_i e da constante de rigidez da junta C. É o valor da carga externa de tração no qual a compressão entre as peças unidas se anula completamente — o ponto em que a junta começa a abrir. Abaixo dela, as peças permanecem comprimidas e a junta se comporta de forma 'inteligente' (o parafuso sente apenas C·P da carga externa, com pequena variação de tensão); acima dela, as peças se separam, e a partir daí toda a carga externa adicional vai direto para o parafuso (que passa a sofrer a carga inteira, com risco de fadiga severa e falha). A separação da junta é, portanto, uma condição que o projeto deve evitar com folga: aplica-se um fator de segurança contra a separação (a carga de separação deve ser bem maior que a carga externa máxima esperada). A fórmula mostra que a carga de separação cresce com a pré-carga (juntas bem apertadas separam mais tarde) — outra razão para usar pré-cargas altas. A separação também causa vazamentos (em juntas com vedação), perda de rigidez e afrouxamento. Garantir que a junta nunca separe sob a carga de serviço é um critério fundamental de projeto de uniões aparafusadas. Informe a pré-carga e a constante de rigidez.
Related Tools
Bolt Load under External Load
Calculate the total tensile force in the bolt when an external load is applied to the joint, F_b = F_i + C·P, from the preload F_i (N), the joint stiffness constant C and the external tensile load P (N). This is one of the most important — and most surprising to the uninitiated — relations of bolted joints: when you apply an external load P trying to 'separate' the parts, the bolt tension does NOT rise from F_i to F_i + P (as intuition suggests), but only to F_i + C·P, where C is typically 0.2-0.4. That is, the bolt only 'feels' a FRACTION of the external load! The reason: most of the external load (1−C)·P merely RELIEVES the compression between the parts (which were compressed by the preload), rather than stretching the bolt more. This is the genius of the preloaded joint — it 'hides' the external load from the bolt. So a well-tightened joint, under a CYCLIC external load (causing fatigue), exposes the bolt to a very small stress variation (proportional to C·ΔP, not ΔP), making it extremely fatigue-resistant. This formula holds while the joint does NOT separate (P below the separation load); above that, the bolt carries the whole load. Enter the preload, stiffness constant and external load.
Residual Member Clamping Force
Calculate the residual clamping force on the members (clamped parts) of a bolted joint under external load, F_m = F_i − (1 − C)·P, from the preload F_i (N), the joint stiffness constant C and the external tensile load P (N). When an external load P tries to separate the parts, it does not go entirely to the bolt — most, (1−C)·P, acts to RELIEVE the compression between the members. The residual force F_m is how much clamping STILL holds the parts together after the external load is applied. This value is crucial for several reasons: while F_m stays POSITIVE (compression), the joint is closed and tight, and the bolt is protected (feels only C·P); if F_m reaches ZERO, the joint SEPARATES (and the bolt takes the whole load). In SEALED joints (gaskets, engine joints, pressurized pipe flanges), the residual member force is what keeps the seal compressed and prevents leaks — so it must stay above a minimum value, even under maximum service load (internal pressure, for example). Computing F_m is essential to ensure the joint stays tight and sealed in operation, and it is the criterion that sets the minimum required preload. Enter the preload, the stiffness constant and the external load.
Joint Stiffness Constant
Calculate a bolted joint's stiffness constant, C = k_b ÷ (k_b + k_m), from the bolt stiffness k_b (N/mm) and the members' (clamped parts) stiffness k_m (N/mm). The constant C (also called bolt load fraction) is the heart of bolted-joint analysis: it tells what FRACTION of an external tensile load is carried by the BOLT, the rest (1−C) being carried by decompression of the MEMBERS. The value of C reveals the elegant, protective behavior of a preloaded joint: since the (massive) members are usually much stiffer than the (thin) bolt, k_m >> k_b, so C is SMALL (typically 0.2-0.4). This means that when an external load P is applied, only a small portion C·P adds to the bolt tension — most of the load (1−C)·P is absorbed by RELIEF of the compression between the parts. That is why the bolt stress variation is small (good fatigue resistance) and why preload is so beneficial. The smaller C (stiff parts, flexible bolt), the better the bolt protection. The constant C appears in all subsequent formulas: bolt load, residual member force, separation load and fatigue safety factor. Enter the bolt stiffness and the members' stiffness.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.