Failure Analysis > Joints > Bolted > Joint Correction Factors

Joint Correction Factors

Joint correction factors are used to correct the margins of safety for effects not captured in the FEM and analytical methods. During the fastener analysis, the bearing stress allowable F_bru is scaled by the cumulative correction factor, K_cf.

MS =	F_bru K_cf	– 1
	σ_bearing (fitting factor)

Important: The following section presents commonly used inputs for bolted joint analysis. These values are not a substitute for test-validated material data.

Countersink, Kcsk The countersink correction factor is dependent on the depth of the fastener countersink and is generally applied to both bearing and BJSFM analysis. For testing, the baseline fastener type is a protruding tension head fastener, K_csk = 1.0. Typical countersink correction factors are 0.7 < K_csk < 0.9.
Joint Eccentricity, Kj The joint eccentricity factor is applied to correct the bending moments present in single shear joints which are not captured in a FEM joining two co-planner meshes. The baseline is a double lap shear joint with equal splice plates, K_j = 1.0. In this case, bending is virtually eliminated. Typical single shear factors for solid laminates are 0.7 < K_j < 0.8. For single lap shear joints joining two honeycomb panels, 0.9 < K_j < 1.0.
Hole Diameter, KD The hole diameter correction factor is dependent on the fastener diameter. For bolt bearing tests, the baseline fastener diameter is 0.25 inches, K_D = 1.0. For larger fasteners, a common practice is to use the baseline bearing allowables determined from test specimens with 0.25 inch diameter holes. In this case a hole diameter factor (K_D < 1.0) is recommended. Typical hole diameter correction factors for 0.375 inch hole diameter, 0.9 < K_D < 0.95, and for a 0.5 inch hole diameter, 0.85 < K_D < 0.9. Usually the hole diameter factor is not recommended for a BJSFM analysis.
Thickness, Kt The thickness correction factor is used to correct the laminate thickness to hole diameter mismatch. The baseline fastener diameter to thickness ratio (D/t) > 1.0, so K_t = 1.0. The thickness correction factor is usually required for bearing analysis only.
Fastener Fit, Kfit The fastener fit correction factor is used to correct the hole tolerances and fiber damage which may occur from over-tightening the fastener. This is particularly a problem in joints where the installed fasteners are removed and reinstalled frequently. The baseline is a permanent expanded sleeve fastener, K_fit = 1.0.
Ke/D The edge distance correction factor is dependent on the edge distance to fastener diameter ratio (e/D). The edge distance is measured from the center of the hole to the free edge. Usually, if e/D < 3.0 then K_e/D < 1.0.
Ks/D The fastener spacing correction factor is dependent on the fastener spacing to fastener diameter ratio (K_s/D). The fastener spacing is measured from the center of each hole. Usually, if s/D < 4.0 then 0.8 < K_s/D < 0.9.
Hybrid Material, Khyb The hybrid material correction factor is used to correct the mismatch in properties of hybrid material systems used at the joint interface. Baseline is a nonhybrid material system, K_hyb = 1.0.
Liquid Shim, Kshiml Shims are commonly used in bolted joints to control structural alignment and produce custom mating surfaces. With liquid shimmed joints, bolt bending can occur which will degrade joint strength. Usually, if the liquid shim thickness > 0.5*D then K_shiml < 1.0.
Solid Shim, Kshims Shims are commonly used in bolted joints to control structural alignment and produce custom mating surfaces. Composite joints are generally less affected by solid shims because bolt bending is virtually eliminated. Tests have shown that degradation of joint shear strength is very gradual with increasing solid shim thickness. Usually, unless an extreme shim thickness is used, K_shims = 1.0.
User Defined The user defined field is reserved for additional user defined corrections.
Cumulative Factor, Kcf The cumulative factor displays the total factor used to scale down the pristine bearing allowable to compute the effective bearing allowable, F_{bru, effective}. This factor is calculated as the product of all joint correction and is not a direct user input.