On October 6, 2006, about 1107 mountain standard time, a Cessna172P, N97811, made a hard landing on runway 19 at the Glendale Municipal Airport, Glendale Arizona. A component in the airplane's nose gear steering assembly broke, and the crew lost directional control of the airplane. The airplane swerved off the runway and impacted a taxiway sign. The airplane's left wing lift strut bent. Angel Aviation, Inc., Glendale, operated the airplane under provisions of 14 CFR Part 91. Neither the certified flight instructor (CFI), who held a commercial pilot certificate, nor the student pilot was injured. The airplane was substantially damaged. Visual meteorological conditions prevailed, and no flight plan had been filed. The instructional flight originated from Glendale about 1015. The CFI stated that prior to taking off, his student and he performed a ground inspection of the airplane. No evidence of any mechanical malfunction was observed. Also, during the flight, no mechanical malfunction occurred. The CFI reported that during the flight with his 30-hour total flight time student, he directed that a series of takeoffs and landing be performed. Initially, the student landed on runway 01. Subsequently, they landed on runway 19. The CFI reported that during their last landing "we had a little bit of crosswind from the left," but we corrected with rudder to keep our nose wheel straight down the centerline. The airplane veered right during rollout, and the CFI took the controls. The CFI additionally indicated that he tried to correct the airplane's track by application of rudder pressure and brakes, but he was not successful. Regarding airframe damage, the National Transportation Safety Board investigator interviewed the Director of Maintenance (DM) for Glendale Aviation. The DM opined that the airplane's nose gear assembly had been overstressed/overloaded during a hard touchdown event. The DM noted the following airframe damage: (1) the nose gear strut was flattened, devoid of nitrogen, its seals were ruptured, and the hydraulic fluid had discharged; (2) the bolt that holds the nose gear torque link together was missing; and (3) four of the lower rubber engines cowling mounts were sheared. The DM opined that the airframe damage, which he observed, resulted from a hard landing. The Safety Board investigator noted that at 1047, the airport reported its surface wind was coming from 120 degrees (true course), or about 108 degrees, magnetic. The wind's speed was 12 knots, with gusts to 18 knots. According to the Federal Aviation Administration's "Airport Facility Directory," runway 19 has an asphalt surface. The runway is 7,150 feet long by 100 feet wide.