Lamina Bending Research Articles

Crushing Behaviour of CFRP Composite Structure

The present paper investigates specific sustained crushing stress (SSCS) of various composite laminate designs and stiffened boxes under axial crushing test. In this regard, an optimum composite crash box design is sought by studying the effect of laminate design and stiffeners on SSCS. Crash boxes were fabricated from carbon/epoxy twill-weave fabrics of [0]4, [45]4 and [0,45]2. The progressive failure with three distinct crushing modes of transverse shearing, lamina bending and brittle fracture was observed for three laminate designs. Two new assembled composite boxes were made from channels and V-shape stiffener and tested in quasi-static condition. Adhesive bonding was used in joining the channelled and stiffened boxes. Measured amount of SSCS for all models were compared to find an optimum crash box. It was found SSCS increases with increasing proportion of 0° plies in the laminate.

Failure model for composite materials under quasi-static crushing conditions

This paper presents a failure model to simulate the crushing mechanisms of fabric composite materials. In order to realize delamination processes and resulting lamina bending modes a multi-layered discretization is applied which is composed of shell and solid elements representing the laminate plies and the resin phase. The differentiation between the two phases enables the implementation of both in-plane failure and delamination fracture criteria and appropriate parametric degradation functions. To verify the fracture and degradation model, quasi-static tests with various compression directions have been carried out. The tests were performed using truncated conical shells of different specimen geometries fabricated with glass/epoxy prepreg. Among a qualitative comparison of the experimental and simulated failure behaviour the numerical model parameters are mainly obtained by curve fitting based on the measured load characteristics. The numerical simulations compare well with the experimental results, proving the applicability of the model for fabric composites under various loading conditions.

Effects of temperature on the crash behaviour of glass fibre reinforced polyamide 12

Environmental conditions such as temperature and humidity influence both mechanical material properties and crash behaviour of composite structures in service. This paper investigates the effect of temperature on the crash behaviour of tubes made of polyamide 12 reinforced with twill 1/3 glass fibre textile. These composite tubes, manufactured from two hat shaped half-tubes welded together. were impact tested at temperatures between −30°C and 90°C using a 45 kg impactor mass released at an average velocity of 10 m/s. Crash characteristics such as mean force and specific absorbed energy arc shown to decrease significantly with rising temperature. The specific absorbed energy dropped almost linearly with respect to temperature changes. The main observed failure mode of the impacted tubes is lamina bending. Furthermore, material samples were tested under three-point-flexural tests employing similar temperature conditions in order to understand the temperature dependency phenomenon. The results were then checked for correlation between crash characteristics and flexural strength. Both crash tests and flexural tests show similar behaviour in relation to the temperature.

The Effects of Crushing Surface Roughness on the Crushing Characteristics of Composite Tubes

The effects of crushing-surface roughness on the energy-absorption capability of graphite and glass-epoxy composite tubes were investigated. Fifty different combinations of fiber, matrix, and specimen ply orientation were evaluated. Two different crushing surface roughnesses were used in this investigation. Crushing surface significantly influences the energy-absorption capability only of tubes that crush in the lamina bending crushing mode; tubes that crush in other modes are not influenced because their lamina bundles do not slide against the crushing surface. Those tubes that crush in the lamina bending mode can achieve higher, lower, or no change in energy-absorption capability as crushing surface roughness increases. If the fiber failure strain of tubes that crush in the lamina bending crushing mode exceeds the matrix failure strain then the energy-absorption capability increases as crushing surface roughness increases. However, if the matrix failure strain exceeds the fiber failure strain then the energy-absorption capability increases as crushing surface roughness decreases. Energy-absorption capability is uninfluenced by crushing surface roughness for tubes that have equal fiber and matrix failure strains.

Role of ethylene in brassinolide-induced rice lamina bending.

Role of ethylene in brassinolide-induced rice lamina bending.

Brassinosteroid-Induced Bending of the Leaf Lamina of Dwarf Rice Seedlings: An Auxin-Mediated Phenomenon

A synthetic brassinosteroid (BR), 2α,3α,22β,23β-tetrahydroxy-24β-methyl-B-homo 7-oxa-5α-cholestan-6-one, an isomer of the growth promoter brassinolide, when applied to seedlings of dwarf rice Oryza sativa var. Tan-ginbozu and Waito-C, induced a significant bending of the second leaf lamina at 100 ng/plant and higher dosages. Promotion of the second leaf sheath elongation, the characteristic response of dwarf rice varieties to gibberellins, was significantly but modestly enhanced by BR at a dosage of 10,000 ng/plant, five orders of magnitude higher than the minimal dosage response to GA3. Gibberellin A3 had no significant effect on the bending of the second leaf lamina, nor did any synergism exist between BR and GA3 in leaf lamina bending or leaf sheath elongation. Neither ethylene nor (2-chloroethyl)phosphonic acid (ethephon) caused the bending of the second leaf lamina, and neither synergized the BR effect. However, IAA and α-naphthaleneacetic acid caused significant bending at 5,000 ng/plant, and both auxins significantly synergized the effect of BR on the bending, IAA being effective at 500 ng/ plant in this regard. The antiauxins, 2,3,5-triiodobenzoic acid (TIBA) and α-(p-chlorophenoxy)isobutyric acid (PCIB) completely nullified both the BR-induced bending and the BR$IAA-synergized bending. The BR-induced bending response may thus be mediated through endogenous auxin.