Basic biomechanical measurements of bone: a tutorial.

The initiation ofdelamination in graphite/epoxy specimens was investigated both analyt ically and experimentally. Three specific laminate families were investigated: [±15n]s, [± 15 n /0n]s, and [0n / ± 15n] s with the normalized effective ply thickness, n, varying from one to five. Delamination initiation was determined to have occurred when a drop in load was detected and a delamination was observed on a replication of the specimen edge. Measured initiation stresses were correlated using the strain energy release rate approach and the Quadratic Delamination Criterion introduced herein. The strain energy release rate approach was unable to accurately correlate data for two of the three laminate fami lies. The data clearly shows that the critical value of strain energy release rate is dependent on ply thickness. The Quadratic Delamination Criterion, an average stress criterion which compares the calculated out-of-plane interlaminar stresses to their related strength param eters, is proposed and shows excel...

Quadratic Stress Criterion for Initiation of Delamination

With the increasing use of fiber reinforced plastic (FRP) composites outside the defense, space and aerospace industries, namely, civilian industries, machining of these materials is assuming a significant role. Unit cost rather than solely performance at any cost will be the consideration for the implementation of FRP composites to consumer industries. The current knowledge of machining FRP composites, unfortunately, is inadequate for its optimum utilization in many applications. This paper presents some observations made on the orthogonal machining of unidirectional carbon fiber reinforced plastic (UD-CFRP) laminates with different fiber orientations. Iosipescu shear test was adopted to evaluate the inplane shear strength of varied fiber angle test specimens. A model for predicting the cutting forces and the dependence of cutting direction on machinability requirements is presented.

On the machining of fiber reinforced plastic (FRP) composite laminates

Compressive failure of composites, part I: Testing and micromechanical theories

Additive manufacturing (AM), more commonly referred to as 3D printing, has become increasingly popular for rapid prototyping (RP) purposes by hobbyists and academics alike. In recent years AM has transitioned from a purely RP technology to one for final product manufacturing. As the transition from RP to manufacturing becomes an increasingly accepted practice it is imperative to fully understand the properties and characteristics of the materials used in 3D printers. This paper presents the methodology and results of the mechanical characterization of acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) 3D printed parts to determine the extent of anisotropy present in 3D printed materials. Specimens were printed with varying raster ([+45/−45], [+30/−60], [+15/−75], and [0/90]) and build orientations (flat, on-edge, and up-right) to determine the directional properties of the materials. Reduced gage section tensile and Isopescu shear specimens were printed and loaded in a universal testing machine utilizing 2D digital image correlation (DIC) to measure strain. Results indicated that raster and build orientation had a negligible effect on the Young’s modulus or Poisson’s ratio in ABS tensile specimens. Shear modulus and shear yield strength varied by up to 33 % in ABS specimens signifying that tensile properties are not indicative of shear properties. Raster orientation in the flat build samples reveal anisotropic behavior in PC specimens as the moduli and strengths varied by up to 20 %. Similar variations were also observed in shear for PC. Changing the build orientation of PC specimens appeared to reveal a similar magnitude of variation in material properties.

Experimental characterization of the mechanical properties of 3D-printed ABS and polycarbonate parts

A history of the losipescu shear test as applied to composite materials is presented along with a description of the test fixture and specimen design. Iosipescu's shear test is compared to similar test techniques, including the asymmetrical four-point bending (AFPB) test. Finally, in-plane and through-the-thickness shear properties measured using the losipescu shear tests are presented for a variety of materials, including a unidirectional graphite/epoxy, random and continuous-fiber sheet molding compounds, and two polymer materials.

The losipescu shear test as applied to composite materials

Recent activities by the present investigators to further develop the losipescu-shear-test method for use with composite materials are summarized Finite-element analyses used to predict the stress states in the specimen are described, with particular emphasis on how they are influenced by the specific test-fixture configuration used These same analytical tools were also used to predict the influence of specimen notch depth, notch angle, and notch-root radius The result was a redesign of the original Wyoming version of the losipescu-shear-test fixture, and the establishment of guidelines for preparing specimens These are discussed in some detail Many references to available literature are included An attempt has been made to put the work performed to date into perspective, to aid the potential user of the losipescu-shear-test method in establishing proper test procedures

Further development of the losipescu shear test method

The nonlinear-viscoelastic response of neat epoxy resin and unidirectional graphite/epoxy and glass/epoxy composites was characterized. Numerical techniques were developed for the efficient evaluation of the viscoelastic parameters in the Schapery integral representation that was used. A microcomputer-based test facility for automatic creep-recovery testing was developed. The time-dependent response of the composites correlated well with predictions obtained using a finite-element micromechanics program with the neat-epoxy-resin viscoelastic data as input.

Nonlinear creep-recovery response of a polymer matrix and its composites

An experimental facility has been developed that is capable of generating any combination of tensile and/or compressive forces on three mutually orthogonal axes of a cruciform-shaped composite specimen. Using this computer-controlled test facility, any stress ratio in biaxial (σ1-σ2) or triaxial (σ1-σ2-σ3) stress space can be evaluated. A description of this electromechanical testing facility, including the reaction frame, test fixture, computer control system and instrumentation is included. Once fully assembled, uniaxial, biaxial and triaxial tests were performed on aluminum and on a carbon/epoxy composite laminate to evaluate the performance of the test facility. Using the data generated from these tests, the performance of many aspects of the triaxial testing facility, including the intra-axis alignment, automated computer testing algorithms, data acquisition algorithms, calibration values and machine compliance, was evaluated. The overall very acceptable performance of the triaxial testing facility is believed to have been demonstrated.

Development of an electromechanical triaxial test facility for composite materials

Various compression test methods for composite materials have been developed during the past few years incorporating specimens of different gage lengths and modes of load introduction. Most of these test methods are not recognized as standards at the present time. Thus the question arises as to whether these various test methods produce similar results.

D. F. Adams

Papers

The losipescu shear test as applied to composite materials

Further development of the losipescu shear test method

Nonlinear creep-recovery response of a polymer matrix and its composites

Development of an electromechanical triaxial test facility for composite materials

Influence of specimen gage length and loading method on the axial compressive strength of a unidirectional composite material