A heat exchanger assembly that addresses the thermal cycling problem to increase the durability of the heat exchanger core by fabricating at least the tube next adjacent to each of the reinforcing members with a cross section adjacent each of the headers including a radius having a partial maximum tube strain energy density and fabricating each of the reinforcing members with a connection section adjacent each of the headers having a reinforcement with a partial maximum strain energy density greater than the partial maximum strain energy density of the adjacent tube.