M1 Abrams - Service Life
The Abrams Main Battle Tank has three usage-based service life limiters: miles driven, engine hours, and equivalent full charges/rounds fired from the gun tube (EFCs). The hull may last indefinitely, and components are replaced and upgraded through maintenance and recapitalization activities as needed to maintain operational capabilities. Therefore, the service life of the tank is defined as the amount of usage that can be expended before a recapitalization or rebuild is required, as defined by the PMO and tank rotational guidance (e.g., Marine Corps Combat Vehicle Evacuation Program).
The primary usage driver is mileage since the tank typically reaches the mileage limit prior to reaching the hours or EFC limits and should be the basis of service life for analysis in the methodology. The Army Abrams Main Battle Tank has an engineering-based service life of 6,000 miles, and the Marine Corps Abrams has a service life of 3,000 miles.
Usage data for Army Abrams tanks at the asset level is available, as well as for other Army aircraft and ground systems. Some limitations exist with service data, especially for ground systems, however, due to inconsistent and decentralized reporting requirements. First, data is only available back to 1993. Secondly, data input relies heavily on the units reporting on a monthly basis, and this poses risks for inconsistent and inaccurate data. Therefore, a requirement should be established that requires usage data to be collected and reported in enterprise-level systems on a routine basis. This will provide enterprise-wide data visibility for use within the OPTEMPO methodology. Usage data for Marine Corps Abrams is not available in a centralized system. It is available in an internal database located with the Marine Corps Systems Command, Armored Fire Support Systems, Tank Systems.
For Army and Marine Corps tanks, a mile or hour in theater is not equal to a mile or hour in the Continental United States (CONUS). Along with increased usage, the type of use that the tanks are experiencing while supporting GWOT operations is accelerating the degradation of the service life of the tank. PEO Ground Combat Systems has determined that the increased weight that tanks carry over the specified design weight, due to up-armor and carrying extra weapons and ammunition, is a significant fatigue factor that decreases the tank’s service life. The increased weight that the tanks carry for combat operations is beyond the designed weight specifications and leads to fatigue on the frame, axles, tracks, suspensions, and other components. This added wear and tear may prevent the tank from reaching its service life before requiring a recapitalization or rebuild.
The Army and Marine Corps Abrams programs do not have a method for quantifying the impact of fatigue on the service lives of the tanks. However, the engineers agreed that a reasonable basis for estimating the impact of fatigue is to apply the percentage increase in weight carried to support combat operations above the tanks’ maximum design specified weight. This fatigue would be applied to wartime usage, as this fatigue typically occurs during combat and contingency operations.
The Army M1A1 program-level example factors total losses, utilization expressed in miles, and fatigue over the lifetime of the program. From program inception through 2008, battle losses totaled four (all resulting from GWOT) and non-combat losses were zero (tank hulls are rarely disposed of as a result of maintenance wash-out; they are refurbished through a recapitalization/rebuild effort for model conversion). Total actual usage is calculated by adding peacetime miles to wartime miles. A fatigue multiplier has been applied to the wartime miles to account for asset fatigue. The M1A1 engineering-based design weight is 63 tons and current carrying weight is 67.5 tons. This equates to a 7.14% increase in weight above engineeringbased design specifications. The fatigue factor is calculated by adding 1 to the 7.14% weight increase. The peacetime miles and the wartime miles, after being weighted by the fatigue multiplier, are summed and divided by the total miles available (6,000 miles per tank times 1,729 active assets). The resulting number is multiplied by the active asset quantity. Battle losses and non-combat losses are then added to this number to determine the number of equivalent lives consumed. The result is 876.32 equivalent lives consumed, or 50.57% [876/1733] of the program service life had been consumed by 2008.
The Marine Corps M1A1 program-level example factors total losses, utilization expressed in miles, and fatigue over the lifetime of the program. By 2008 battle losses totaled 16 and non-combat losses were zero (tank hulls are never disposed of as a result of maintenance wash-out; they are refurbished through a recapitalization/rebuild effort for model conversion). Total actual usage is determined by summing the current mileage on the tanks, for a total of 1,012,667 miles. Since the PMO does not capture wartime mileage and peacetime mileage for their tanks, an estimate was provided for determining wartime and peacetime mileage based on current data trends. The estimate for wartime mileage is 25% of total mileage and the estimate for peacetime/non-combat mileage is 75% of total mileage. Applying the aforementioned percentages to estimate the number of miles supporting combat and non-combat operations results in 253,166.75 wartime miles (25% of 1,012,667 miles) and 759,500.25 peacetime miles (75% of 1,012,667 miles).
A fatigue multiplier has been applied to the wartime miles to account for asset fatigue. The M1A1 engineering-based design weight is 63 tons and current average carrying weight for the MC M1A1 tanks is 70.86 tons. This equates to a 12.48% average increase in weight above engineering-based design specifications that would be applied to wartime/combat mileage. The fatigue factor is calculated by adding one to the average 12.48% weight increase. The peacetime miles and the wartime miles, after being weighted by the fatigue multiplier, are summed and divided by the total miles available (3,000 miles per tank times 416 tanks). The resulting number is multiplied by the active asset quantity. Battle losses and non-combat losses are then added to this number to determine the number of equivalent lives consumed. The result is 364.09 equivalent lives consumed, or 84.26% [364/432] of the program service life had been consumed. Data applied to this example is as of August 2007.
The Marine Corps Systems Command, Armored Fire Support Systems, Tank Systems noticed a trend that tanks are currently experiencing increased hours of operation, while accumulating less mileage, which indicates that the tanks are running but sitting idle for extended periods of time. It has been noted that possibly by 2010 the main usage driver may become hours for the M1A1 if this trend continued in theater. This would cause the tanks to meet their hours-based service life limit prior to that based on mileage, meaning that the service life analysis should be based on hours. The methodology allows for these changes to be incorporated into the methodology as they are determined, to more accurately determine program aging.
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