Improving Reliability in the Next Generation of US Army Platforms Through PoF Analysis, Part 1
Tuesday, July 31, 2012 | Geetha V. Chary, Gary S. Drake, and Ed Habtour
Published studies and audits have documented that a significant number of U.S. Army systems are failing to demonstrate established reliability requirements. In order to address this issue, the Army developed a new reliability policy in December 2007 which encourages use of cost-effective reliability best practices. The intent of this policy is to improve reliability of Army systems and material, which in turn will have a significant positive impact on mission effectiveness, logistics effectiveness and life-cycle costs.
Under this policy, the Army strongly encourages the use of mechanical and electronics physics of failure (PoF) analysis for military systems. At the U.S. Army Materiel Systems Analysis Activity (AMSAA), PoF analyses are conducted to support contractors, program managers (PMs) and engineers on systems in all stages of acquisition from design, to test and evaluation (T&E) and fielded systems.
This paper discusses using the PoF approach to improve reliability of military products. Physics of failure is a science-based approach to reliability that uses modeling and simulation to eliminate failures early in the design process by addressing root-cause failure mechanisms in a CAE environment. The PoF approach involves modeling the root causes of failure such as fatigue, fracture, wear, and corrosion. CAE tools have been developed to address various loads, stresses, failure mechanisms, and failure sites. This paper focuses on understanding the cause and effect of physical processes and mechanisms that cause degradation and failure of materials and components.
A reliability assessment case study of circuit cards consisting of dense circuitry is discussed. System-level dynamics models, component finite element models and fatigue-life models were used to reveal the underlying physics of the hardware in its mission environment. Outputs of these analyses included forces acting on the system, displacements of components, accelerations, stress levels, weak points in the design and probable component life. This information may be used during the design process to make design changes early in the acquisition process when changes are easier to make and are much more cost-effective.
Design decisions and corrective actions made early in the acquisition phase leads to improved efficiency and effectiveness of the T&E process. The intent is to make fixes prior to T&E to reduce test time and cost, allow more information to be obtained from test and improve test focus. PoF analyses may be conducted for failures occurring during test to better understand the underlying physics of the problem and identify the root cause of failures which may lead to optimal fixes for problems discovered, reduced test-fix-test iterations and reduced decision risk. The same analyses and benefits mentioned above may be applied to systems which are exhibiting failures in the field.
Design-in reliability, failure mechanisms, fatigue, physics of failure, shock, thermal overstress, vibration.
Many Army programs have taken an iterative loop approach, i.e., test-fix-test, with an emphasis on beginning the testing process early and learning from soldiers' experiences with the equipment. However, as time goes on, the cost to fix failures that were not addressed earlier in design can become very large and could adversely affect operational effectiveness and increase life-cycle costs.