Shinji Ogihara

Mechanical and thermal properties and water absorption of jute fiber reinforced poly(butylene succinate) biodegradable composites

The poly(butylene succinate) (PBS) biodegradable composites reinforced with jute fibers were developed. The effect of fiber content (10–60wt%) on the properties and water absorption of jute/PBS biodegradable composites was studied. The effect of alkali, silane, and combined alkali and silane surface treatment on the properties and water absorption of jute/PBS composites was investigated. The mechanical properties of surface treated jute/PBS composites were significantly higher than those of untreated ones. Compared with alkali or silane treatment, the combined alkali and silane surface treatment showed better mechanical properties of jute/PBS composites. The best mechanical properties of jute/PBS composites were achieved at 50wt% in this study, which showed an increase in tensile strength by 517.9%, tensile modulus by 3529.8%, flexural strength by 302.6%, and flexural modulus by 1949.1% compared with those of PBS resin. Fractured surface morphologies of composite specimens exhibited an improvement of interfacial fiber–matrix adhesion in the composites reinforced with surface-treated jute fibers. The surface-treated jute/PBS composites having good fiber–matrix adhesion resulted in stable composites with better thermal stability than untreated jute/PBS composites. The water absorption amount of the composites increased with increasing the fiber content. The surface-treated jute/PBS composites showed relatively lower water absorption behavior compared to untreated ones.

Mechanical properties of fiber/matrix interface in polymer matrix composites

This paper reviews the mechanical properties of interface adhesion between the fiber and matrix mainly by interpreting the authors’ past articles. First, the methods for evaluating interface mechanical properties are described considering micromechanical testing using single-fiber composite specimens. In particular, the test-type dependence of the obtained interfacial strength is discussed, and this paper suggests that the cruciform specimen technique is an appropriate testing method. Then, this paper presents another way to obtain interface properties that is extracted from a bulk composite test. Moreover, the time and temperature dependence of the interface strength and the interface failure envelope under a combined stress state are described, respectively. Interface toughness is also discussed at the end of this paper, and it is implied that the value might be much lower than those presented in many conventional articles.

Mechanical property enhancement of aligned multi-walled carbon nanotube sheets and composites through press-drawing process

A solid-state drawing and winding process was done to create thin aligned carbon nanotube (CNT) sheets from CNT arrays. However, waviness and poor packing of CNTs in the sheets are two main weaknesses restricting their reinforcing efficiency in composites. This report proposes a simple press-drawing technique to reduce wavy CNTs and to enhance dense packing of CNTs in the sheets. Non-pressed and pressed CNT/epoxy composites were developed using prepreg processing with a vacuum-assisted system. Effects of pressing on the mechanical properties of the aligned CNT sheets and CNT/epoxy composites were examined. Pressing with distributed loads of 147, 221, and 294 N/m showed a substantial increase in the tensile strength and the elastic modulus of the aligned CNT sheets and their composites. The CNT sheets under a press load of 221 N/m exhibited the best mechanical properties found in this study. With a press load of 221 N/m, the pressed CNT sheet and its composite, respectively, enhanced the tensile strength by 139.1 and 141.9%, and the elastic modulus by 489 and 77.6% when compared with non-pressed ones. The pressed CNT/epoxy composites achieved high tensile strength (526.2 MPa) and elastic modulus (100.2 GPa). Results show that press-drawing is an important step to produce superior CNT sheets for development of high-performance CNT composites.

Study on impact perforation fracture mechanism in PMMA

Many studies on the hypervelocity impact problem in metallic materials have been conducted [1±3]. In these studies, rail guns, powder guns and light gas guns are used to launch projectiles. The correlation of target fracture morphology, absorbed energy, the penetration depth, and the crater diameter=volume with impact velocity is investigated. In the present study, polymeric materials are used as target material. The objective of the present study is to examine the fracture mechanism of polymeric materials by high velocity impact tests and quasistatic perforation tests. A target material is polymethylmethacrylate (PMMA). The target plate sizes are 115 mm3 115 mm and 214 mm 3 214 mm. Thickness of target specimens, t, are 1, 3, 5 and 10 mm. The target specimens are ®xed between two plates with circular holes. The diameters of the holes, D, are 100 mm and 200 mm. The high velocity impact tests and quasi-static perforation tests are impact test and perforation test into a ®xed circular plate. In high velocity impact tests, the experimental apparatus is composed of an air compressor and an air gun. Stainless and PMMA spherical projectiles, whose diameter is ,11 mm are launched by impact testing machine at various velocities up to 200 m sy1. In quasi-static perforation tests, the target specimen is perforated by a steel bar having a spherical head whose diameter is 10 mm. The tests are performed by using a universal testing machine. The cross head speeds are 0.5, 5.0 and 50.0 mm miny1. In high velocity impact tests, four typical fracture forms of targets and PMMA projectiles, respectively, were veri®ed. Fracture forms of targets are de®ned as ricochets, cracks, breaks and perforates. Those for projectiles are de®ned as intact, cracked, broken and shattered. Fig. 1 shows a ballistic phase diagram which indicates the relationships between the impact velocity and the fracture morphology of targets and projectiles. Fig. 2 shows the relation between impact velocity and perforated hole area. It is found that the hole area becomes similar to the maximum section area of the projectile at impact velocities above a certain value. For impact velocities below 100 m sy1, the perforation fracture is dominated by bending deformation. For impact velocities above 100 m sy1, bending deformation is very small before the projectile perforates the target. Fig. 3 shows typical load±displacement curves obtained by quasi-static perforation tests (D x88 100 mm, t x88 1 mm). It is seen that in this range of

Accurate full-field optical displacement measurement technique using a digital camera and repeated patterns

In this study, a novel, fast, and accurate in-plane displacement distribution measurement method is proposed that uses a digital camera and arbitrary repeated patterns based on the moiré methodology. The key aspect of this method is the use of phase information of both the fundamental frequency and the high-order frequency components of the moiré fringe before and after deformations. Compared with conventional displacement methods and sensors, the main advantages of the method developed herein are its high resolution, accuracy, speed, low cost, and easy implementation. The effectiveness is confirmed by a simple in-plane displacement measurement experiment, and the experimental results indicate that an accuracy of 1/1000 of the pitch can be achieved for various repeated patterns. This method is useful for various applications ranging from the study of displacement and strain distributions in materials science, the biomimetics field, and mechanical material testing, to secure the integrity of infrastructures.

Numerical simulation of damage progression and fracture in structures made of 3D woven ceramic matrix composites

This paper proposes numerical simulation to predict damage progression and critical strength in structural components made of 3D woven ceramic matrix composites (CMCs). This method implements three numerical approaches with the commercial finite element method. (i) Damage models are used to predict damage initiation and propagation of CMCs. (ii) The failure criterion based on the Weibull volumetric statistical strength model is implemented to take into account the size effects of fiber-bundle strength. (iii) The nonlocal damage theory is implemented to confirm the mesh independence of the results and the convergence of computation. To verify the accuracy of the two damage models, simulations of smooth SiC/SiC specimens were performed. Furthermore, several kinds of open-hole SiC/SiC tensile test were simulated to verify the accuracy of the proposed numerical simulation. Finally, the proposed numerical simulation was validated by detailed comparisons of experiment and simulation.

A probabilistic SCG model for transverse cracking in CFRP cross-ply laminates under cyclic loading

This paper presents a probabilistic fatigue model for transverse cracking in CFRP cross-ply laminates. First, a delayed fracture model for a crack in a brittle material subjected to cyclic loading was established on the basis of the slow crack growth (SCG) concept in conjunction with the Weibulls probabilistic failure model. Second, the above probabilistic delayed fracture model was applied to transverse cracking in cross-ply laminates during cyclic loading. The stress distribution and the length of the unit element were calculated with the aid of a shear lag analysis. The transverse crack density was expressed as a function of maximum stress, stress ratio and number of cycles using the parameters associated with the Paris equation and the Weibull distribution in addition to the mechanical properties. Unknown parameters were determined from experiment data for three kinds of cross-ply laminates to reproduce the transverse crack density against the number of cycles. The parametric studies using the obtained parameters revealed the effects of the Weibull modulus, crack propagation exponent and stress ratio on evolution of transverse cracking under fatigue loading.

Effects of surface treatment on mechanical and thermal properties of jute fabric-reinforced poly(butylene succinate) biodegradable composites

Biodegradable composites based on poly(butylene succinate) (PBS) and unidirectional plain jute fabrics have been developed. These composites were fabricated by compression molding of sandwiching 4–7 jute fabric layers between five and eight layers of PBS sheets. Surface modification of the jute fabric by alkali and combined alkali-silane treatments was investigated. The effects of surface modification on the mechanical and thermal properties of jute fabric/PBS biodegradable composites were studied. The mechanical properties of surface-treated jute fabric/PBS biodegradable composites were significantly higher than those of untreated ones. Compared with the alkali treatment, the combined alkali-silane treatment showed higher mechanical properties of the jute fabric/PBS biodegradable composites. The alkali-silane-treated jute fabric/PBS biodegradable laminated composite with six reinforced fabric layers (47.5u2009wt.%) achieved the best mechanical properties in this study, which showed an increase in tensile strength by 16.4%, tensile modulus by 10.8%, flexural strength by 24.2%, and flexural modulus by 21.9% compared with those of untreated one. Fractured surface morphologies of tensile specimens exhibited an improvement of interfacial fiber-matrix adhesion in the PBS biodegradable composites reinforced with surface-treated jute fabric. Thermal stability of the jute fabric/PBS biodegradable composites was remarkably to be intermediate between the PBS resin and the jute fabric. Surface-treated jute fabric/PBS biodegradable composites having good interfacial fiber-matrix adhesion resulted in stable composites with better thermal stability than that of untreated ones.

Numerical validation of split Hopkinson pressure bar technique for evaluating tensile mechanical properties of CFRP laminates

The present study proposes a simple numerical simulation technique for the split Hopkinson pressure bar (SHPB) and then investigates the experimental conditions for composite materials in a tensile-loading SHPB. The following issues were investigated through experiment and numerical simulation: (i) the effects of the cross section and acoustic mismatch between the jig with a slit and screw and the input/output bars on the loading condition and (ii) the effects of the duration time of the applied load and the acoustic impedance mismatch on the stress–strain curve obtained by SHPB testing. From the numerical simulation results, the following conclusions were found: (i) the proposed jig with a slit and screw can apply an ideal one-dimensional displacement to a specimen and (ii) the material characterization of a composite material by SHPB testing might be possible by optimizing a longer duration time if the acoustic mismatch is greater.

Fragmentation Analysis of Single-Fiber Carbon Composites

The effects of fiber surface oxidization and sizing treatment on both fiber strength distribution and fragmentation behavior in single carbon fiber epoxy composites are investigated experimentally. Based on the above experimental data, the fiber/matrix interfacial properties are discussed. It is found that the effect of fiber surface treatment on the fiber strength distribution is small and that the interfacial shear stress increases when applying fiber surface oxidization and sizing treatment in the carbon fiber/epoxy system used in the present study. K e y w o r d s : fragmentation test, single carbon fiber composite, interfacial shear stress, fiber surface treatment