The size effect in the failure of a hybrid adhesive joint of a metal with a fiber-polymer composite, which has been experimentally demonstrated and analytically formulated in preceding two papers, is here investigated numerically. Cohesive finite elements with a mixed-mode ß-acture criterion are adopted to model the adhesive layer in the metal-composite interface. A linear tractionseparation softening law is assumed to describe the damage evolution at debonding in the adhesive layer. The results of simulations agree with the previously measured load-displacement curves of geometrically similar hybrid joints of various sizes, with the size ratio of 1:4:12. The effective size of the fracture process zone is identified from the numerically simulated cohesive stress profile at the peak load. The fracture energy previously identified analytically by fitting the e.xperimentally observed size effect cwves agrees well with the fracture energy of the cohesive crack model obtained numerically by optimal fitting of the test data. ] metal-composite joints. For a double-lap joint of steel and fiberpolymer composite analyzed and tested at Northwestern University (see Fig. 1 (test series 2 in Ref.[1])), the dominant stress singularity exponent was found to be A = -0.459 -I-0.06/ (/' = \f^) for the inner corners and / = -0.219 for the outer comers [2]. Since the stress singularity at the inner comer of the joint is stronger than at the outer one, a crack will emanate from the inner corner and propagate along the weakest plane in the bimaterial joint. This plane of propagation will lie either in the metal-composite interface or in the fiber composite.Although the stress singularity exponent at the inner comers is very close to the exponent of -1/2 at the crack tips, the analysis of fracture at the bimaterial corner is complicated by the fact that the elastic energy release rate corresponding to a singularity exponent > -1/2 is zero. As such, the energetic argument of linear elastic fracture mechanics (LEFM) cannot directly be used to characterize the crack initiation from the comer. Rather, one must take into account the development of a finite fracture process zone (FPZ) at the inner comer, which can be quite large when dealing with a quasi-brittle material such as fiber composite [2,3]. For a propagating crack, the size of the FPZ is approximately constant, a material characteristic. The consequence is a size effect on the strength of the metal-composite joints.The size dependence of the nominal strength of hybrid joints has been studied experimentally and theoretically in the preceding papers [1,2]. For example, when the strength values measured in test series 2 of Ref.[1] are plotted in a logarithmic scale, the nominal strengths of geometrically similar metal-c.omposite joints are seen to decrease with the joint size as seen in Fig. 2.It was found that the size dependence of joint strength can be expressed by a formula similar to the classical type 2 size effect law [4][5][6][7] that has been shown to apply to homogeneous qua...