Predicting Mechanical Properties of Metal Matrix Syntactic Foams Reinforced with Ceramic Spheres

A model is presented that predicts peak stress, minimum stress, average stress, densification strain, and composite density in order to determine the energy absorption per unit volume and energy absorption per unit mass of metal matrix syntactic foams reinforced with hollow ceramic spheres subjected to unconstrained compression testing. Comparison of predictions to experimental data for Al-A206 and Al-A380 matrices of various heat treatments reinforced with Al2O3 spheres of various sizes, size ranges, and wall thickness to sphere diameter ratios show good agreement. Introduction Metal matrix syntactic foams (MMSF’s) may be considered as underdeveloped when compared to open cell or closed cell foams. Though many studies have been conducted where selected properties of single matrix and reinforcement composition and reinforcement size combinations have been reported, little information is available on how to intelligently tailor these materials to obtain desired mechanical properties [1-19]. Moreover, these studies rarely report all of the mechanical properties of interest to engineers. Critical review of the available literature is further complicated by the fact that there is not widespread agreement on the definitions of certain critical properties of MMSF’s as they differ from conventional metal foams. For example, the definition of plateau stress (i.e. the single stress level at which a foam material absorbs a significant amount of strain before densification) is problematic in these materials as the stress varies significantly between the peak and densification. Densification strain is even more arbitrary as some studies report properties to fixed strains (for example 30% strain or 50% strain), while others report densification strain at such high strain that the stresses are much higher than the peak stress. Parts 1 and 2 of this series [20, 21] defined the plateau stress as the average stress between the strain at peak stress and the strain at densification. For consistency, the densification strain was defined as the strain at which the foam sustains a stress equal to the initial peak stress. This definition follows that used in metal foamsmaterials in which the peak stress and plateau stress are similar, where densification is considered to occur when the stress rises above the plateau stress (i.e. peak stress) [22]. This definition is also consistent with analyses of syntactic foams containing metallic hollow spheres [23]. Using these definitions the authors reported the effects of sphere dimensions, matrix composition and mechanical and physical properties on the foam’s density, unconstrained compressive peak stress, plateau stress, densification strain, toughness (energy absorption per unit volume), and specific energy Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 13 AUG 2012 2. REPORT TYPE Journal Article 3. DATES COVERED 13-08-2012 to 13-08-2012 4. TITLE AND SUBTITLE Predicting Mechanical Properties of Metal Matrix Syntactic Foams Reinforced with Ceramic Spheres 5a. CONTRACT NUMBER w56hzv-08-c-0716 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) J. Ferguson; J. Santa Maria; B. Schultz; P. Rohatgi 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) University of Wisconsin,Milwaukee Materials Department CEAS,Milwaukee,WI,53201 8. PERFORMING ORGANIZATION REPORT NUMBER ; #23253 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) U.S. Army TARDEC, 6501 E.11 Mile Rd, Warren, MI, 48397-5000 10. SPONSOR/MONITOR’S ACRONYM(S) TARDEC 11. SPONSOR/MONITOR’S REPORT NUMBER(S) #23253 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT A model is presented that predicts peak stress, minimum stress, average stress, densification strain, and composite density in order to determine the energy absorption per unit volume and energy absorption per unit mass of metal matrix syntactic foams reinforced with hollow ceramic spheres subjected to unconstrained compression testing. Comparison of predictions to experimental data for Al-A206 and Al-A380 matrices of various heat treatments reinforced with Al2O3 spheres of various sizes, size ranges, and wall thickness to sphere diameter ratios show good agreement. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT Same as Report (SAR) 18. NUMBER OF PAGES 15 19a. NAME OF RESPONSIBLE PERSON a. REPORT unclassified b. ABSTRACT unclassified c. 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