Härtelt, M.

Liesching, B.

Rohde, M.

Südmeyer, I.

KITopen

Residual stresses and shear strength of laser brazed Al2O3/steel-jointsI. Südmeyer, B. Liesching, M. Härtelt, M. Rohde Laser Brazing Process Motivation Finite Element Modelling  Argon steelceramicbrazeinsulationCO2-laser beamStress Analysiscourse of temperature020040060080010000 1000 2000670s 1800 sstress analysistime [s]temperature [°C]pyrometer  sample geometry160.2412 16Increase of shear strength by reduction of residual stresses  inlaser brazed Al2O3/steel-jointsmaterial Incusil ABA CB4materials propertiestemperature [°C]laser heating zone1. laser heating 2) coolingtemperature [°C]1st : simulation of brazing processs2nd step: stress analysisThe ceramic pellet exhibits two areas of stress maxima:stress maximum at friction surfacestress maximum at joining surface Fracture Probabilitystress σ1 [MPa]                           propertyAl2O3 C45E Ag-Cu-In-Ti Ag-Cu-Ticompany Friatec AG - Morgan Chem. Brazetecdensity ρ / g/cm³ 3.95 7.85 9.7 9.63strength σ / MPa 350 560-710 338 72Youngs modulus E / GPa 380 210 76 0.23* thermal conductivity λ, W/mK 38 44 166 20* CTE α, 10-6 m/K 8.4 11.0 18.2 170* effect of element size on σ1max sequential temperature-stress-analysis:calculated temperature distribution provides as  loading for stress calculation evaluation of calculated stress:σ1-stress in ceramic pellet are considered to befailure relevant  Shear Testingtempered plungerYoungs modulus, CTE, thermal conductivity and σ were implied as thermal dependent paramters.  STAUi t value of σ1max on joining surface is explicitly dependent on element size (singularity) value of σ1max on the friction surface is independent of element size PclampingFceramic steelbrazenpuexperimental: material parameterfe-interfaceoutput: Pf , Vefffinite-element modelling:geometry, loadingspontaneous fracture: m, σ0     crack growth: n, B, (p)numerical integration∫∫∫ΩΩ⎟⎟⎠⎞⎜⎜⎝⎛, 0eqAmdAdσσl l i k f f t (STAU)*σ1 - stress distribution (fem)PF: fracture loadR:   sample radiusτ: fracture stressm: Weibull modulus τ = PFπ · R²F = i n + 1F: fracture probabilityi:  sample numbern: number of sampleselement size: 0 05 element size: 0 5τ0* mGauß laser profile MPa -non structured 21 4.9Tophead laser profilenon structured 25 1 9Weibull evaluation of shear testsoca  r s  o  rac ure local risc of fracturemaximum fracture riskLocation of σ1max and maximum local risk of fracture agree with real  crack starting point of laser brazed joints1st principal stress σ1 [MPa]σ1max300 µmσ1maxlocal risc of fracture maximum fracture riskσ1max  .   .element size: 0.05 element size: 0.58x10-46x1007x100e probability PfCu-interlayer lead to:  reduction of σ1max reduction of Pfinfluence of Cu-Interlayer on σ1max and Pfincrease of  joint strength through:  homogenized laser profile Cu-interlayer and  .non structured + Cu-layer (500µm) 39 1.5non structured + Cu-layer (1000µm) 71 1.7structured steel 39 2.1∗τ0 = τ (F=63,2%) XRD-measurementAl2O3-ceramic metalxceramic x t lMPa 389 251 226 151200 200 200 100- 500 1000 1000maximum of stress σ1maxbraze layerµmCu-interlayercalculation  not finishedceramic ceramic ceramicbraze braze brazeSEM- images of laser brazed  jointsinfluence of seam geometry04x10-4fractureconformity of experiments & modelsSummary structured steel surfaceShear testing of laser brazed joints Increase of joint strength and reduction of reliability through  heating with homogenized laser  intensity profile,  Cu-interlayer and  structured steel surfacesXRD measurement were carried out by IAM-WK, KIT – Campus South textures in ceramics lead to large inhomogeneity of x-ray signals  general compliance of calculated and measured residual stressestangentialaxialmeasuring pointsxceramic xsteels ee437 MPaFirst principle stress in ceramic pellet404 MPa300 µm 300 µm 300 µmsteel steel steelvariation of seam contour  (fem)15,8 16161617262 MPaFinite Element Modelling of laser brazing process A reduction of element size in the ceramic/braze interface affects an explicitincrease of σ1max (singularity) Thin metal carrier evoke bending of ceramic high σ1-values Reduction of σ1max through Cu-interlayer Seam geometry braze has an value of σ1max singularityXRD measurement of residual stress General compliance of measured and calculated axial and tangential stress, but  large deviation according to textures in the ceramicKIT – University of the State of Baden-Wuerttemberg andNational Research Center of the Helmholtz AssociationHigh performance sliding and friction systems on the basis of ceramic componentsECerS XII Stockholm, SwedenJune 19-23 2011         The authors thank the Deutsche Forschungsgemeinschaft for suppporting the Sonderforschungsbereich 483 „High performance sliding and friction systems on the basis of engineering ceramics“. 491 MPa  value of σ1max on joining surface is explicitly dependent on seam geometryCalculation of fracture probability Agreement of calculated local risk of fracture and real crack configuration Reduction of calculated fracture probability through Cu-interlayer correspond to experimental results 

Residual stresses and shear strength of laser brazed Al₂O₃/steel-joints

https://publikationen.bibliothek.kit.edu/220085110/3815923

Residual stresses and shear strength of laser brazed Al₂O₃/steel-joints

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