[ { "id": "authors:rtzbs-ypj97", "collection": "authors", "collection_id": "rtzbs-ypj97", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200520-074532493", "type": "book_section", "title": "Experimental Investigation of Failure in Viscoelastic Elastomers Under Combined Shear and Pressure", "book_title": "Challenges in Mechanics of Time-Dependent Materials and Processes in Conventional and Multifunctional Materials", "author": [ { "family_name": "Alkhader", "given_name": "Maen", "clpid": "Alkhader-M" }, { "family_name": "Knauss", "given_name": "Wolfgang", "clpid": "Knauss-W-G" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" } ], "contributor": [ { "family_name": "Antoun", "given_name": "Bonnie", "clpid": "Antoun-B" }, { "family_name": "Qi", "given_name": "H. Jerry", "clpid": "Qi-H-Jerry" }, { "family_name": "Hall", "given_name": "Richard", "clpid": "Hall-Richard" }, { "family_name": "Tandon", "given_name": "G. P.", "clpid": "Tandon-G-P" }, { "family_name": "Lu", "given_name": "Hongbing", "clpid": "Lu-Hongbing" }, { "family_name": "Lu", "given_name": "Charles", "clpid": "Lu-Charles" } ], "abstract": "An experimental approach, based on Split Hopkinson Pressure Bar (SHPB) apparatus, is developed to elucidate failure of viscoelastic elastomers under combined shear and high pressures such as are encountered in explosive and/or armor-impact scenarios. In this experimental arrangement, thin cylindrical polyurea specimens with an aspect ratio (Diameter to thickness) greater or equal to 15 are tested, up to failure, using Split Hopkinson Pressure Bar (SHPB). Specimens with large aspect ratio are used to guarantee the close approximation of a triaxial state of stress in the specimen upon loading; hence the measured normal stress would be approximately equal to the hydrostatic pressure in the specimen. Friction at the loading interfaces forces the stress state to deviate from uniformity, restrict both the circumferential and radial displacements and lead to the development of shear stresses and strains. Hence, induced failure occurs under conditions combining high-strain-rate, high pressure and shear stresses. By using this setup, repeatable failure modes were detected and elucidated using finite element simulations.", "doi": "10.1007/978-1-4614-4241-7_8", "isbn": "978-1-4614-4240-0", "publisher": "Springer", "place_of_publication": "New York, NY", "publication_date": "2013-10-25", "pages": "55-62" }, { "id": "authors:nt0d1-wam47", "collection": "authors", "collection_id": "nt0d1-wam47", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200520-144612061", "type": "book_section", "title": "Experimental arrangement for measuring the high-strain-rate response of polymers under pressures", "book_title": "Mechanics of Time-Dependent Materials and Processes in Conventional and Multifunctional Materials", "author": [ { "family_name": "Alkhader", "given_name": "Maen", "clpid": "Alkhader-M" }, { "family_name": "Knauss", "given_name": "Wolfgang", "clpid": "Knauss-W-G" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" } ], "contributor": [ { "family_name": "Proulx", "given_name": "Tom", "clpid": "Proulx-T" } ], "abstract": "This study aims to investigate the high-strain-rate shear response of viscoelastic elastomeric coatings at large strains and under elevated levels of hydrostatic pressure. Results of this study shed light on the combined effects of deformation rate and pressure which might promote a transition from viscoelastic to glassy behavior. This work utilizes a Split Hopkinson Pressure Bar (SHPB) apparatus in conjunction with a customized version of the recently proposed Shear Compression Specimen (SCS) which consists of a polymer gage section with two metal ends that remain essentially rigid during deformation. Detailed finite element simulations were used to customize the adopted specimen, to determine its proper dimensions and promote its functionality. The customized specimen permits subjecting the tested specimen to a state of uniform pressure and shear stress, while allowing for measuring pressure, shear stress and shear strain directly. Results obtained using the customized specimen, which are included in this paper, illustrate its usefulness in measuring the effect of high-strain-rate, large strain and hydrostatic pressure on the shear stress-strain response of viscoelastic elastomers.", "doi": "10.1007/978-1-4614-0213-8_20", "isbn": "978-1-4614-0212-1", "publisher": "Springer", "place_of_publication": "New York, NY", "publication_date": "2011-05-11", "pages": "139-144" }, { "id": "authors:mttpk-ken14", "collection": "authors", "collection_id": "mttpk-ken14", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200601-143119734", "type": "book_section", "title": "The influence of pressure on the large deformation shear response of a Polyurea", "book_title": "Time Dependent Constitutive Behavior and Fracture/Failure Processes", "author": [ { "family_name": "Alkhader", "given_name": "Maen", "clpid": "Alkhader-M" }, { "family_name": "Knauss", "given_name": "W. G.", "clpid": "Knauss-W-G" }, { "family_name": "Ravichandran", "given_name": "G.", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" } ], "contributor": [ { "family_name": "Proulx", "given_name": "Tom", "clpid": "Proulx-T" } ], "abstract": "A new shear-compression experiment is developed to characterize the influence of hydrostatic pressure on the shear constitutive response of nearly incompressible viscoelastic materials undergoing large deformations. In this design, a uniform torsional shear stress is superposed on a uniform hydrostatic compressive state of stress generated by axially deforming samples confined by a stack of thin steel disks. The new design is effective in applying uniform multiaxial compressive strain while preventing buckling and barreling during inelastic deformation. In addition, it allows for the direct measurement of the stress and strain fields during the deformation history. The new shear-compression setup is developed to aid in characterizing the influence of pressure or negative dilatation on the shear constitutive response of viscoelastic materials in general and Polyurea in particular. Experimental results obtained with this technique illustrate the significant increase in the shear stiffness of polyurea under moderate to high hydrostatic pressures.", "doi": "10.1007/978-1-4419-9794-4_40", "isbn": "978-1-4419-9498-1", "publisher": "Springer", "place_of_publication": "New York, NY", "publication_date": "2011-04-15", "pages": "287-295" }, { "id": "authors:asy7m-a7e51", "collection": "authors", "collection_id": "asy7m-a7e51", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181204-132724650", "type": "book_section", "title": "Microtensile tests with the aid of probe microscopy for the study of MEMS materials", "book_title": "Materials and Device Characterization in Micromachining III", "author": [ { "family_name": "Chasiotis", "given_name": "Ioannis", "orcid": "0000-0001-6521-8332", "clpid": "Chasiotis-Ioannis" }, { "family_name": "Knauss", "given_name": "Wolfgang G.", "clpid": "Knauss-W-G" } ], "contributor": [ { "family_name": "Vladimirsky", "given_name": "Yuli", "clpid": "Vladimirsky-Y" }, { "family_name": "Coane", "given_name": "Philip J.", "clpid": "Coane-P-J" } ], "abstract": "Mechanical tests of thin films require novel and sophisticated methods that can address the geometry and microstructure of the films. A new method of micro-tensile testing of MicroElectroMechanical Systems (MEMS) films has been demonstrated. An improved apparatus has been designed and implemented to measure the elastic tensile properties. (Young's modulus, Poisson's ration and tensile strength) of surface micromachined polysilicon specimans. The tensile specimans are dog-bone shaped ending in a large paddle for convenient electrostatic or, in the improved apparatus, UV adhesive gripping. The test section of the specimens is 400\u00b5m long with 2\u00b5mx50\u00b5m cross section. The method employs Atomic Force Microscope (AFM) acquired surface topologies of deforming specimans to determine (fields of) strain by way of the Digital Image Correlation method (DIC). With this method, high strength of non- linearly behaving materials under different environmental conditions can be tested by measuring the strains directly on the surface of the film with nanometer resolution in in-place and out-of-plane measurements.", "doi": "10.1117/12.395616", "isbn": "9780819438317", "publisher": "Society of Photo-optical Instrumentation Engineers (SPIE)", "place_of_publication": "Bellingham, WA", "publication_date": "2000-08-11", "pages": "96-103" }, { "id": "authors:rbwrz-m0881", "collection": "authors", "collection_id": "rbwrz-m0881", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180813-091037460", "type": "book_section", "title": "Mechanical properties of thin polysilicon films by means of probe microscopy", "book_title": "Materials and Device Characterization in Micromachining", "author": [ { "family_name": "Chasiotis", "given_name": "Ioannis", "orcid": "0000-0001-6521-8332", "clpid": "Chasiotis-Ioannis" }, { "family_name": "Knauss", "given_name": "Wolfgang G.", "clpid": "Knauss-W-G" } ], "contributor": [ { "family_name": "Friedrich", "given_name": "Craig R.", "clpid": "Friedrich-C-R" }, { "family_name": "Vladimirsky", "given_name": "Yuli", "clpid": "Vladimirsky-Y" } ], "abstract": "A new method for tensile testing of thin films is being developed. An electrostatic grip apparatus was designed and implemented to measure the elastic and ultimate tensile properties (Young's modulus, Poisson's ratio and tensile strength) of surface micromachined polysilicon specimens. The tensile specimens are 'dog-bone' shaped ending in a large 'paddle' for electrostatic gripping. The test section of the specimens is 400 micrometers long and with 2 micrometer X 50 micrometer cross section. The method employs Atomic Force Microscope (AFM) or Scanning Tunneling Microscope (STM) acquired surface topologies of deforming specimens to determine (fields of) strains. By way of the method of Digital Image Correlation (DIC), the natural surface roughness features are used as distributed markers. The effect of markers artificially deposited on the surface is examined computationally. Also the significance of other parameters on property measurements, such as surface roughness, has been examined computationally. Initial results obtained using the tensile test apparatus are presented.", "doi": "10.1117/12.324072", "isbn": "9780819429711", "publisher": "Society of Photo-optical Instrumentation Engineers (SPIE)", "place_of_publication": "Bellingham, WA", "publication_date": "1998-09-01", "pages": "66-75" }, { "id": "authors:f0j0s-p8s69", "collection": "authors", "collection_id": "f0j0s-p8s69", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181119-141500977", "type": "book_section", "title": "Round-Robin Tests of Modulus and Strength of Polysilicon", "book_title": "Microelectromechanical Structures for Materials Research", "author": [ { "family_name": "Sharpe", "given_name": "W. N.", "clpid": "Sharpe-W-N" }, { "family_name": "Brown", "given_name": "S.", "clpid": "Brown-S" }, { "family_name": "Johnson", "given_name": "G. C.", "clpid": "Johnson-G-C" }, { "family_name": "Knauss", "given_name": "W.", "clpid": "Knauss-W-G" } ], "contributor": [ { "family_name": "Brown", "given_name": "Stuart", "clpid": "Brown-S" } ], "abstract": "The Young's modulus and strength of polysilicon specimens manufactured in the same production run were measured in four different laboratories. Specimens subjected to in-plane bending were tested at U. C. Berkeley and at Failure Analysis Associates, and tensile measurements were made at Caltech and Johns Hopkins. All specimens were produced at the Microelectronics Center of North Carolina (MCNC). \n\nIn bending, the Young's modulus for specimens nominally 2 \u00b5m thick was measured as 174 GPa and 137 GPa; whereas in tension, a value of 132 GPa was obtained. Modulus values of 136 GPa and 142 GPa were measured in tension on specimens nominally 1.5 \u00b5m and 3.5 \u00b5m thick. Strengths of the brittle polysilicon were 2.8 and 2.7 GPa in bending and 1.3 GPa for both thicknesses in tension.\n\nThese preliminary results were presented at Symposium N - Microelectromechanical Structures for Materials Research at the Materials Research Society meeting in April 1998. This paper is a short overview of the test methods \u2014 each of which is described elsewhere \u2014 and a documentation of the results presented at that time.", "doi": "10.1557/PROC-518-57", "isbn": "9781558994249", "publisher": "Materials Research Society", "place_of_publication": "Warrendale, PA", "publication_date": "1998-04", "pages": "Art. No. 57" }, { "id": "authors:0jnxk-hhn26", "collection": "authors", "collection_id": "0jnxk-hhn26", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200716-135556381", "type": "book_section", "title": "Volume/Shear Interaction in Glassy Polymers", "book_title": "Progress and Trends in Rheology V", "author": [ { "family_name": "Knauss", "given_name": "W. G.", "clpid": "Knauss-W-G" } ], "contributor": [ { "family_name": "Emri", "given_name": "I.", "clpid": "Emri-I" } ], "abstract": "It has been demonstrated in the past that the nonlinear time- or rate-dependent shear behavior of glassy polymers is susceptible to volumetric changes. Following from models based on free volume effects in the glass transition range it has been shown analytically that many effects of nonlinear behavior could possibly be traced to volumetric changes and associated dilatational internal clock mechanisms.", "doi": "10.1007/978-3-642-51062-5_7", "isbn": "978-3-642-51064-9", "publisher": "Springer-Verlag", "place_of_publication": "Heidelberg", "publication_date": "1998", "pages": "21" }, { "id": "authors:r8gpc-ajy15", "collection": "authors", "collection_id": "r8gpc-ajy15", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:KNAafr89", "type": "book_section", "title": "Time dependent fracture of polymers", "book_title": "Advances in fracture research : proceedings of the 7th International Conference on Fracture (ICF-7), Houston, Tex., 20-24 March 1989", "author": [ { "family_name": "Knauss", "given_name": "W. G.", "clpid": "Knauss-W-G" } ], "contributor": [ { "family_name": "Salama", "given_name": "K." }, { "family_name": "Ravi-Chandar", "given_name": "K." }, { "family_name": "Taplin", "given_name": "D. M. R." }, { "family_name": "Rama Rao", "given_name": "P." } ], "abstract": "The fracture behavior of polymers is reviewed with emphasis on the time dependent aspects of the problem. Following a delineation of the history of crack propagation investigations in linearly viscoelastic materials, the effects of temperature and solvent environment are examined besides the special effects arising from fatigue loading. These phenomena are examined for both crosslinked and uncrosslinked polymers. Some special consideration is given to the phenomena connected with craze formation in amorphous homopolymers as well as in crystalline materials as exemplified by polyethylene. Finally, status of analytical tools and formulations of fracture problems involving non-linearly viscoelastic material behavior is delineated by means of some examples.", "isbn": "0080343430", "publisher": "Pergamon Press", "place_of_publication": "New York", "publication_date": "1989", "pages": "2683-2711" }, { "id": "authors:a2z2w-q7y23", "collection": "authors", "collection_id": "a2z2w-q7y23", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151125-113158676", "type": "book_section", "title": "Fatigue Failure in Linearly Viscoelastic Masterials", "author": [ { "family_name": "Williams", "given_name": "M. L.", "clpid": "Williams-M-L" }, { "family_name": "Knauss", "given_name": "W. G.", "clpid": "Knauss-W-G" }, { "family_name": "Wagner", "given_name": "F. R.", "clpid": "Wagner-F-R" } ], "abstract": "The thermodynamic approach to the fracture of linearly viscoelastic materials presented earlier is extended to include fatigue. The theoretical analysis of the growth of an internal spherical flaw due to a uniformly distributed,\noscillatory input of displacement in the radial direction predicts a growth-rest type of flaw growth which depends upon the properties of the media and the loading frequency. Comparison of these results with experimental\ncrack growth data for a pre-cracked sheet specimen subjected to an oscillatory displacement input discloses a qualitative similarity in behavior. It is, therefore, believed that the analytical model employed is representative of real flaw behavior and that its study can reveal the main features of macroscopic flaw-growth.", "publisher": "Chemical Propulsion Information Agency", "publication_date": "1966" }, { "id": "authors:35ez5-7fe83", "collection": "authors", "collection_id": "35ez5-7fe83", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151125-113438967", "type": "book_section", "title": "Time-Dependent Failure of Viscoelastic Materials Under Cyclic Loads", "author": [ { "family_name": "Knauss", "given_name": "W. G.", "clpid": "Knauss-W-G" } ], "abstract": "The problem of failure in viscoelastic materials under cyclic strain histories is treated theoretically by using a fracture model based on the theory of rate processes. Failure times in constant, uniaxial strain tests are compared with failure times encountered\nin sinusoidal strain histories. The dependence of the latter on the mean strain, the size of the strain variation and its frequency is illustrated. It is pointed out that for certain conditions a difference in the failure times in constant or cyclic strain histories may be\nmasked entirely by statistical data scatter. Finally the failure of solid propellant fuels under cyclic loading is discussed in the light of the results derived for a continuum rubber.", "publisher": "Chemical Propulsion Information Agency", "publication_date": "1966" }, { "id": "authors:2g0fj-g2k30", "collection": "authors", "collection_id": "2g0fj-g2k30", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100519-091001010", "type": "book_section", "title": "On the mechanical properties of an H-C rubber", "author": [ { "family_name": "Knauss", "given_name": "Wolfgang G.", "clpid": "Knauss-W-G" } ], "abstract": "The material properties of H-C binder including dynamic shear compliance, relaxation modulus, creep compliance, ultimate stress and ultimate strain are reported. Further useful information in the form of Modified Power Law and Prony Series curve fits are included as well as a master curve of reduced stress vs. strain. \n\nAll tests are performed using standard procedures; however some inconsistency in material properties has been found. It was further determined that the time-temperature shift principle is not directly applicable in its simplest form; however, upon postulating two molecular mechanisms responsible for gross deformations it is found that each one can be associated with a different characteristic glass transition temperature such that, e.g. the dynamic compliance J(w) is the sum of two compliances J_\u03b1 and J_\u03b3 \n\nJ(w,t) = J_\u03b1(w, T^\u03b1_glass) + J_\u03b3(w, T^\u03b3_glass) \n\nwhich individually follow the time temperature superposition principle.", "publisher": "Caltech Library", "publication_date": "1963-11" } ]