Experimental and numerical investigation on bending and compressive behavior of carbon-epoxy sandwich panel with novel M-shaped core

Present paper has experimentally and numerically investigated the mechanical behavior of composite sandwich panel with novel M-shaped lattice core subjected to three-point bending and compressive loads. For this purpose, a composite sandwich panel with M-shaped core made of carbon fiber has been fabricated in this experiment. In order to fabricate the sandwich panels, the vacuum assisted resin transfer molding (VARTM) has been used to achieve a laminate without any fault. Afterward, polyurethane foam with density of 80 kg/m3 has been injected into the core of the sandwich panel. Then, a unique design was presented to sandwich panel cores. The study of force-displacement curves obtained from sandwich panel compression and three-point bending tests, showed that an optimum mechanical strength with a considerable lightweight. It should be noted that the experimental data was compared to numerical simulation in ABAQUS software. According to the results, polyurethane foam has improved the flexural strength of sandwich panels by 14% while this improvement for compressive strength is equal to 23%. As well as, it turned out that numerical results are in good agreement with experimental ones and make it possible to use simulation instead of time-consuming experimental procedures for design and analysis.

EVALUATION OF AXIAL LOAD-BEARING CAPACITY OF CONCRETE COLUMNS STRENGTHENED BY A NEW SECTION ENLARGEMENT METHOD

The objective of this study is to evaluate the axial load-bearing capacity of section-enlargement concrete columns. To reach the objection, a new strengthened method in which columns are jacketed with a large welded octagonal stirrup at the center and four spiral stirrups at the corners of column is developed. The new section-enlargement method avoids interrupting existing columns and improves the reliability of strengthened part, besides, the confining stress generated by octagonal stirrup and spiral stirrups enhances the compressive strength and deformability of strengthened columns. In addition, sixteen large-scale concrete columns strengthened by the new strengthened method were tested under axial compressive loads. The experimental results show that the axial compression ratio of existing column generates stressstrain lag in strengthened part and decreases the load-bearing capacity of specimens; the stirrups in strengthened part significantly enhance the axial load-bearing capacity of specimens. According to confinement conditions, the cross-section of specimens is divided into five parts and the confinement factor for each part is calculated to establish the prediction models for the load-bearing capacity of specimens. Furthermore, by comparing the results between the developed model and existing models, the developed model has high accuracy in evaluating the load-bearing capacity of strengthened columns.

Principles of Stress-Strength Modelling of the Highly Thermally Loaded Materials—The Influence of an Effect of Strength Differential on the Material Effort

This paper presents an improvement in the Huber–Mises–Hencky (HMH) material effort hypothesis proposed by Burzyński. Unlike the HMH hypothesis, it differentiates the plastic effort between compression and tensile load states, and links shear with tensile limit. Furthermore, it considers the fact that construction materials do not have infinite resistance in the pure tensile hydrostatic load state, which was proved by the static load experiment performed on St12T heat-resistant steel. The asymmetry between tensile and compressive loads is captured by the elastic region asymmetry coefficient ϰ, which was established by experiment for St12T steel in the temperature range between 20 °C and 800 °C.

Modelling vibrations of axial piezoelectric generator with active base

Modelling of an axial-type piezoelectric generator (PEG) is considered. PEG is an integral part of the system for converting mechanical vibration energy from the environment into electrical energy. The energy generator has an axial type of the configuration of elements, aimed on using bending and compressive loads simultaneously on piezoelectric elements. The base of the generator is made as an active pinching. A feature of PEG is that the generator has two types of piezoelectric elements: (1) elements located on the substrate in the form of a bimorph and (2) piezoelectric elements of a cylindrical shape, fixing the generator base, located on the same axis. PEG has a symmetrical structure about the center of proof mass. The results of modal and harmonic analysis of vibrations are given for vibration excitation of the PEG base in a certain frequency range. The analysis of the output characteristics is given.

Mechanical Properties of Wheat Grains at Compression

Hook’s law for evaluation of the modulus of elasticity of wheat grains and its general behaviour under compressive loads were studied. Whole specimens were subjected to compressive loading between metal parallel plates. The mechanical properties of grains were determined in terms of average failure strengths of grain bran and whole grain; deformation; and modulus of elasticity. The mechanical properties of very dry grains of the winter wheat Triticum aestivum L. with the moisture content of 10.3% were studied. The failure strength of grain bran was 4.43 MPa at the deformation of 10.7%, and the failure strength of whole grains was 4.88 MPa at the deformation of 13.5%. The modulus of elasticity of grains was 43.67 MPa. The apparent energy density at bran failure strength was 0.261 MJ·m−3, and 0.470 MJ·m−3 on the level of grain failure strength of the whole grain. The bran border structure of central inner part of grains was studied using microscope digital sections of longitudinal cuts of the grains using the image computer processing method. The area proportion of starch and pericarp of the border parts of grains was studied to describe the border texture of central sections of grains.

Walking Biomechanics and Spine Loading in Patients With Symptomatic Lumbar Spinal Stenosis

Symptomatic lumbar spinal stenosis is a leading cause of pain and mobility limitation in older adults. It is clinically believed that patients with lumbar spinal stenosis adopt a flexed trunk posture or bend forward and alter their gait pattern to improve tolerance for walking. However, a biomechanical assessment of spine posture and motion during walking is broadly lacking in these patients. The purpose of this study was to evaluate lumbar spine and pelvic sagittal angles and lumbar spine compressive loads in standing and walking and to determine the effect of pain and neurogenic claudication symptoms in patients with symptomatic lumbar spinal stenosis. Seven participants with symptomatic lumbar spinal stenosis, aged 44–82, underwent a 3D opto-electronic motion analysis during standing and walking trials in asymptomatic and symptomatic states. Passive reflective marker clusters (four markers each) were attached to participants at T1, L1, and S2 levels of the spine, with additional reflective markers at other spinal levels, as well as the head, pelvis, and extremities. Whole-body motion data was collected during standing and walking trials in asymptomatic and symptomatic states. The results showed that the spine was slightly flexed during walking, but this was not affected by symptoms. Pelvic tilt was not different when symptoms were present, but suggests a possible effect of more forward tilt in both standing (p = 0.052) and walking (p = 0.075). Lumbar spine loading during symptomatic walking was increased by an average of 7% over asymptomatic walking (p = 0.001). Our results did not show increased spine flexion (adopting a trunk-flexed posture) and only indicate a trend for a small forward shift of the pelvis during both symptomatic walking and standing. This suggests that provocation of symptoms in these patients does not markedly affect their normal gait kinematics. The finding of increased spine loading with provocation of symptoms supports our hypothesis that spine loading plays a role in limiting walking function in patients with lumbar spinal stenosis, but additional work is needed to understand the biomechanical cause of this increase.

A Study of Mechanoelectrical Transduction Behavior in Polyvinyl Chloride (PVC) Gel as Smart Sensors

Polyvinyl chloride (PVC) gels are soft electroactive polymers being researched for soft robotic applications. Sensing properties of these electroactive polymers have not been investigated in detail in regard to fundamental mechanoelectrical transduction behavior, but this smart material has been shown to exhibit a detectable response to external stimuli. This study shows PVC gels to be an extremely sensitive material when undergoing mechanoelectrical transduction and explores some response dependencies and proposes a theoretical framework for mechanoelectrical transduction within the gel. The work presented here also uncovers a very interesting phenomena under extremely low compressive loads during the initial contact with the gel. This phenomenon is attributed to a surface tension creeping motion onto the loading surface with an accompanying polarity inversion in the sensing signal relative to fully loaded gels in compression. Experimental work on hysteresis was also completed showing very little memory in steady state mechanoelectrical response to repeated stepped loading cycles. This study demonstrates the mechanoelectric ability of PVC gels to perform in sensing experiments and acts as a fundamental framework to further broaden the applications of PVC gel sensors.

A Contribution to Analytical Solutions for Buckling Analysis of Axially Compressed Rectangular Stiffened Panels

Analytical solution to the buckling problems of stiffened panels subjected to in-plane compressive loads is presented. The total potential energy functional of stiffened panel is obtained by the summation of that of a line continuum and stiffened panel derived from elastic principles of mechanics. Minimizing the resulting equation with respect to deflection coefficient and rearranging gives the expression for obtaining the buckling load of stiffened panel. Exact deflection functions were substituted directly in the new solution and various edge conditions were considered in this analysis. Obtained results were compared with analytical results of previous works. The method is computationally efficient for complex edge conditions and gives high numerical accuracy.