Bolt Tensile Stress
Calculate the tensile stress in a bolt, σ = F_b ÷ A_t, from the total bolt tensile force F_b (N) and the tensile stress area A_t (mm²). It is the basic strength check of a tensioned bolt: the acting stress (force over resisting area) must be below the material strength with a safety margin. The force F_b is the total load the bolt carries — in a preloaded joint, the preload plus the fraction of external load reaching the bolt (F_i + C·P). The resulting stress is compared with the proof strength S_p (the limit up to which the bolt can be loaded without permanent deformation — typically 85-90% of yield) or the ultimate strength, per the criterion. The bolt strength class (marked on the head: 8.8, 10.9, 12.9 metric; or SAE grades 2, 5, 8) sets these allowable stresses — a class 8.8 bolt has a proof strength of 580-600 MPa, a 12.9 reaches ~970 MPa. Verifying σ does not exceed the allowable, considering preload and service load, is essential: overloaded bolts yield (losing preload) or break. With the fatigue and separation checks, it defines the tensioned joint's safety. Enter the total bolt force and the tensile area.
Result
—
Tensão de tração em parafuso
A tensão de tração em um parafuso é σ = F_b ÷ A_t, a partir da força total de tração no parafuso F_b e da área de tensão A_t. É a verificação básica de resistência de um parafuso tracionado: a tensão atuante (força dividida pela área resistente) deve ser menor que a resistência do material com margem de segurança. A força F_b é a carga total que o parafuso suporta — em uma junta pré-carregada, é a pré-carga mais a parcela da carga externa que chega ao parafuso (F_i + C·P). A tensão resultante é comparada com a tensão de prova S_p (o limite até onde o parafuso pode ser carregado sem deformação permanente — tipicamente 85-90% do escoamento) ou com a resistência última, conforme o critério. A classe de resistência do parafuso (gravada na cabeça: 8.8, 10.9, 12.9 em métricos; ou graus SAE 2, 5, 8) define essas tensões admissíveis — um parafuso classe 8.8 tem tensão de prova de 580-600 MPa, um 12.9 chega a ~970 MPa. Verificar que σ não excede o admissível, considerando a pré-carga e a carga de serviço, é essencial: parafusos sobrecarregados escoam (perdem a pré-carga) ou rompem. Junto com a verificação de fadiga e de separação, define a segurança da união tracionada. Informe a força total no parafuso e a área de tensão.
Related Tools
Bolt Tensile Stress Area (Metric)
Calculate the tensile stress area of a metric-thread bolt, A_t = (π/4)·(d − 0.9382·p)², from the nominal diameter d (mm) and the thread pitch p (mm). The tensile stress area is the EFFECTIVE cross-section resisting tension in a threaded bolt — and it is NOT the nominal-diameter area (the smooth cylinder) nor the root-diameter area (the thread bottom). Because of the helical thread geometry, tensile rupture occurs at an intermediate section, and tests showed it corresponds to an effective diameter equal to the average of the pitch and root diameters, leading to the formula with the 0.9382·p term (a geometric constant of the ISO metric thread, 60° triangular profile). The tensile area is the fundamental parameter for all bolt strength calculations: preload, tensile stress, proof load and ultimate strength are all found by multiplying A_t by the corresponding material stress. Using the wrong area (the larger nominal-diameter one) would overestimate strength and lead to undersized joints. Bolt tables list A_t for each diameter-pitch combination; this formula computes it for any metric thread. Enter the nominal diameter and the thread pitch.
True Stress
Calculate the true stress, σ_t = s × (1 + e), from the engineering stress s (MPa) and the engineering strain e. Engineering stress uses the specimen's initial area, but during a tensile test the real cross-section shrinks; true stress corrects this using the instantaneous area (assuming constant volume in the uniform region), always giving a higher value than engineering stress. It is essential to build the true stress-strain curve and model strain hardening (σ = K·εⁿ). The result is in the same unit as the input stress. Enter the engineering stress and strain.
Paper Breaking Length
Compute the breaking length (self-rupture) of paper, L = tensile index / 9.80665, in km — the length of a paper strip that, hung from one end, would break under its own weight. It is an intuitive, classic way to express tensile strength, independent of grammage. Common papers break around 3–8 km; high-strength papers, more. Enter the tensile index (N·m/g).
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.