A two-part adhesive formulation comprising: an adhesive part A comprising: a monomer amount of a (meth)acrylate ester monomer; a crosslinker amount of a polyfunctional monomer; an anti-oxidant; a free-radical polymerization inhibitor; an adhesion promoter system including an etching agent and an adhesion promoter, to improve cured adhesive strength to a substrate, wherein said etching agent includes inorganic acids such as sulfuric acid, nitric acid, hydrofluoric acid, hydrochloric acid, hydrobromic acid, perchloric acid, phosphoric acid, or monophosphate; and organic acids such as acetic acid, tannic acid or formic acid, and wherein said adhesion promoter includes phosphate esters, mono-functional phosphates, difunctional phosphates, and combinations thereof; and a free-radical polymerization initiator; a first impact modifier; and a toughening agent; and an activator part B present in a 1:1 weight ratio to said part A, said part B comprising: an activator monomer amount of said (meth)acrylate ester monomer; a second impact modifier; and a free-radical polymerization accelerator; each of said part A and said part B having separate storage stability of at least 300 days at 23° C (when packed under a nitrogen atmosphere), wherein the first and second impact modifiers are core-shell structured impact modifiers, and wherein the first and second impact modifiers are each independently at least one of methacrylate butadiene styrene, nitrile rubber, a block copolymer of styrene and butadiene, high rubber graft having 60 percent rubber, or a combination thereof; and wherein said toughening agent comprises at least one of copolymers of ethylene acrylic elastomer, chloro-sulphonated polyethylene, poly(methyl methacrylate) grafted rubber, neoprene, styrene acrylonitrile copolymer, or a combination thereof. an adhesive part A comprising: a monomer amount of a (meth)acrylate ester monomer; a crosslinker amount of a polyfunctional monomer; an anti-oxidant; a free-radical polymerization inhibitor; an adhesion promoter system including an etching agent and an adhesion promoter, to improve cured adhesive strength to a substrate, wherein said etching agent includes inorganic acids such as sulfuric acid, nitric acid, hydrofluoric acid, hydrochloric acid, hydrobromic acid, perchloric acid, phosphoric acid, or monophosphate; and organic acids such as acetic acid, tannic acid or formic acid, and wherein said adhesion promoter includes phosphate esters, mono-functional phosphates, difunctional phosphates, and combinations thereof; and a free-radical polymerization initiator; a first impact modifier; and a toughening agent; and a monomer amount of a (meth)acrylate ester monomer; a crosslinker amount of a polyfunctional monomer; an anti-oxidant; a free-radical polymerization inhibitor; an adhesion promoter system including an etching agent and an adhesion promoter, to improve cured adhesive strength to a substrate, wherein said etching agent includes inorganic acids such as sulfuric acid, nitric acid, hydrofluoric acid, hydrochloric acid, hydrobromic acid, perchloric acid, phosphoric acid, or monophosphate; and organic acids such as acetic acid, tannic acid or formic acid, and wherein said adhesion promoter includes phosphate esters, mono-functional phosphates, difunctional phosphates, and combinations thereof; and wherein said etching agent includes inorganic acids such as sulfuric acid, nitric acid, hydrofluoric acid, hydrochloric acid, hydrobromic acid, perchloric acid, phosphoric acid, or monophosphate; and organic acids such as acetic acid, tannic acid or formic acid, and wherein said adhesion promoter includes phosphate esters, mono-functional phosphates, difunctional phosphates, and combinations thereof; and a free-radical polymerization initiator; a first impact modifier; and a toughening agent; and an activator part B present in a 1:1 weight ratio to said part A, said part B comprising: an activator monomer amount of said (meth)acrylate ester monomer; a second impact modifier; and a free-radical polymerization accelerator; each of said part A and said part B having separate storage stability of at least 300 days at 23° C (when packed under a nitrogen atmosphere), an activator monomer amount of said (meth)acrylate ester monomer; a second impact modifier; and a free-radical polymerization accelerator; each of said part A and said part B having separate storage stability of at least 300 days at 23° C (when packed under a nitrogen atmosphere), wherein the first and second impact modifiers are core-shell structured impact modifiers, and wherein the first and second impact modifiers are each independently at least one of methacrylate butadiene styrene, nitrile rubber, a block copolymer of styrene and butadiene, high rubber graft having 60 percent rubber, or a combination thereof; and wherein said toughening agent comprises at least one of copolymers of ethylene acrylic elastomer, chloro-sulphonated polyethylene, poly(methyl methacrylate) grafted rubber, neoprene, styrene acrylonitrile copolymer, or a combination thereof.