Masaaki Itabashi

Mechanical characterization of unidirectional CFRP thin strip and CFRP cables under quasi-static and dynamic tension

Under uniaxial tension, full stress-strain curves up to fracture and mechanical properties of a variety of CFRP cables having different structures are evaluated experimentally at three strain rates ranging from quasi-static (10-5 s-1) to dynamic (102 s-1). Such properties as tensile strength, chord or tangent modulus, strain at tensile strength and absorbed energy per unit volume are obtained. Experimental difficulties on stress and strain measurements and specimen fastening are overcome by introducing special instrumental arrangements and an expansive-cement fastening technique. For all cables, at quasi-static (10-5 s-1) and intermediate (10-2 s-1) strain rates, the stress-strain relation is linear. On the other hand, at a dynamic (102 s-1) strain rate, the stress-strain relation is non-linear and all cables tend to increase their elastic modulus and tensile strength. This obviously leads to increase of the absorbed energy per unit volume under dynamic tension. However, the strain at tensile strength remains almost the same at all strain rates. Thus, from a consideration based on the fracture strain criterion, it is concluded that strain rate insensitivity is assured for all cables.

Simplified compression bending test method for advanced composites

In the past, one of the authors has proposed a new bending test method, namely a compression bending test. The test was based on buckling and is suitable for advanced composites because the undesirable stress concentration from the loading nose is removed. The original paper dealt with the measurement of the bending strength and successive papers with the methodology used to measure the bending modulus. In the present paper, a new device has been designed by which the total system is drastically simplified. In addition, systematic comparison of all methods has been carried out. During a series of experiments, the superiority of the present compression bending test method was demonstrated.

Dynamic mechanical behavior of HTPB dummy composite propellant

The uniaxial dynamic tensile properties of HTPB (hydroxy-terminated polybutadiene) dummy solid composite propellant at high strain rates of about 103 S-1, strongly demanded but never obtained hitherto, was acquired using the KHKK (Kawata-Hashimoto-Kurokawa-Kanayama) one bar method of block-to-bar type established for the purpose of evaluating dynamic tensile stress-strain behavior up to breaking strain. Quasi-static to medium strain rate tensile tests at strain rates ranging from 10-3 to 10-1 s-1 were also performed and compared with dynamic behavior. The dependence of mechanical properties on strain rate is clarified. Particularly, the tensile strength and modulus increase drastically at dynamic strain rates of the order of 103 s-1. High velocity impact-absorbing ability is revealed, although the dynamic breaking strain shows values of an order similar to the static results. Fractured surfaces of filled HTPB dummy propellant after testing were also examined. The difference of fracture appearances in stat...

Eccentric compression bending test for CFRP pipe

This paper reports a new test method to evaluate the bending strength of composite pipes. In the past, we proposed a compression bending test method to get more reliable bending strength values than the conventional three- or four-point bending test. This compression bending was successfully applied not only to flat CFRP coupons but also to slender CFRP pipes. However, if the diameter of the pipe is relatively large, this compression bending is not necessarily appropriate. Therefore, as a step forward to accurate determination of compression bending, an eccentric compression bending test method is tried in the present paper.

The Japanese Building Standard Law and a series of steels for earthquake-resistant building structures

This contribution refers to the Building Standard Law in Japan and by focusing especially on the part which is related to seismic forces, shows how to protect humans and property (in Japan) from earthquake disasters. In 1981, the Law was amended to introduce plastic design into architecture. In order to enhance the ability of the new seismic proof structural design method, a new series of steels was developed and manufactured in 1994. Material damage induced by repeated earthquakes is investigated in this paper. The newly produced pre-damaged SN490B steel (one of the new steels) is tested and evaluated under dynamic tension. The pre-damage is introduced by pre-fatiguing or pre-straining. Compared with SM490A steel (a conventional steel), the remaining mechanical properties of the SN490B steel resemble those of SM490A even under dynamic tension. However, once plastic deformation has developed in the SN490B steel, it loses the capability of accepting large deformation when used in structural members. Tests ...

Mechanical Characterization of Solids in High Strain Rate Tension

Extensive studies on mechanical characterization of solids of wide categories in high strain rate tension are reported. A bird’s-eye view of breaking strain and absorbed energy per unit volume, not only stress, is given for uniaxial tension in strain rate level of 10−3 s−1 ~103 s−1 never studied enough hitherto. In these studies, solutions of long standing questions are included. Classification of solids ranging from metals, polymers (energy elasticity and entropy elasticity) and composites to ceramics, from the standpoint of impact-resistant properties in high strain rates is also summarized.

Analysis of tensile behavior of CFRP strand cables with various structures

This article presents experimental analysis and related discussion on tensile behavior of CFRP strand cables with various structures, never studied in detail hitherto. The influence of structure itself and helix angle on the tensile behavior under quasi-static loading of CFRP strand cable is investigated. While the structure of the cable does not much affect its tensile properties, too large a helix angle reduces the cable tensile strength, chord modulus and absorbed energy. The reduction of the strength may be attributed obviously to shear stress induced in helical strings of the cable. A newly developed strain measuring system works successfully for very precise determination of small strains up to break in such stiff materials. Notable characteristics are also specified as failure criterion for the unique helical array of CFRP.

Development of Compression Bending Test Method for Advanced Composites - A Review

This paper reviews a series of our research works in developing a compression bending test method. This idea was invented to get rid of undesirable effect of loading devices in a conventional 3or 4-point bending test. Starting from the basic concept, some refinements of data reduction methodology and some advancements of test fixtures are described in conjunction with the application to flat coupons as well as pipe configurations. The most recent work of an eccentric compression bending test is also reviewed. INTRODUCTION region and this is the main benefit of the present method. Wisnom 15, 6/ applied the same idea to evaluate the compressive failure stress and/or strain of composites rather than bending strength. In the present paper, the essence of our works is presented step by step. The major subjects are (1) how to measure the bending strength 111, (2) how to measure the bending modulus /8, 9/, and (3) a simplification of the test device /10/. The above works were conducted using flat coupons whereas test results for pipe configuration / l l / are also reported in the present paper. Further, an eccentric compression bending test /12/, which is an advancement of the compression bending test, is briefly reviewed. It is well known that the bending strength of CFRP coupon is strongly affected by the stress concentration due to a stiff loading device in a 3or 4-point bending test. The works of Whitney /1 / and Cui and Wisnom 121 are some examples addressing this stress concentration effect. The work of Hojo, et al. 13/ focused on reducing the stress concentration by inserting a soft film between the test specimen and the loading devices and this idea was adopted in the J IS (Japanese Industrial Standard) as a recommendation /4/. To compensate for this undesirable effect of the stress concentration due to the loading device, we have developed an additional approach. That is, if an axial load is applied to a column, it will buckle (Euler buckling) and eventually the bar will break at the middle of the span. The present review focuses on the compression bending caused by Euler buckling. In this case, there is no loading device at around the failure HOW TO MEASURE THE BENDING STRENGTH As was mentioned in the Introduction, the present idea is based on the Euler buckling of a pin-ended column. Figure 1 shows the half length of the present specimen. The experimental methodology is based on the Euler buckling of the specimen. The bending moment at the midspan A is

On the effects of loading velocity in T-peeling and lap-shearing strengths of FRP

Mechanical properties in T-peeling and lap-shearing of FRP under dynamic load obtained by using the one-bar method are reported. Comparing these with mechanical properties under quasi-static load, positive velocity dependence is clarified in T-peeling strength and lap-shearing strength vs. loading velocity relations. The effects of fiber orientation (reinforcement combination) and of the nature of the fiber itself on the strengths of specimens are also clarified.

Characterization of Highly Anisotropically Reinforced Solids in High Velocity Tension

The characterization method and obtained results for unidirectionally reinforced Kevlar composite in high strain rate tension up to 103/s are stated.