Experimental Investigation on Environmentally Sustainable Cement Composites Based on Wheat Straw and Perlite

Environmentally sustainable cement mortars containing wheat straw (Southern Italy, Apulia region) of different length and dosage and perlite beads as aggregates were prepared and characterised by rheological, thermal, acoustic, mechanical, optical and microstructural tests. A complete replacement of the conventional sand was carried out. Composites with bare straw (S), perlite (P), and with a mixture of inorganic and organic aggregates (P/S), were characterised and compared with the properties of conventional sand mortar. It was observed that the straw fresh composites showed a decrease in workability with fibre length decrease and with increase in straw volume, while the conglomerates with bare perlite, and with the aggregate mixture, showed similar consistency to the control. The thermal insulation of the straw mortars was extremely high compared to the sand reference (85–90%), as was the acoustic absorption, especially in the 500–1000 Hz range. These results were attributed to the high porosity of these composites and showed enhancement of these properties with decrease in straw length and increase in straw volume. The bare perlite sample showed the lowest thermal insulation and acoustic absorption, being less porous than the former composites, while intermediate values were obtained with the P/S samples. The mechanical performance of the straw composites increased with length of the fibres and decreased with fibre dosage. The addition of expanded perlite to the mixture produced mortars with an improvement in mechanical strength and negligible modification of thermal properties. Straw mortars showed discrete cracks after failure, without separation of the two parts of the specimens, due to the aggregate tensile strength which influenced the impact compression tests. Preliminary observations of the stability of the mortars showed that, more than one year from preparation, the conglomerates did not show detectable signs of degradation.

P071 Osteoid osteoma in children: About 15 cases

Background Osteoid osteoma (OO)also called osteoblastoma, if the localization is in the spine, is a benign osteoblastic tumor of variable clinical expression, depending on the location of the lesion. It represents 2% to 3% of bone tumours and 15% of benign bone tumours in children. It affects mainly older children and adolescents and most often occurs in the lower limb, especially the femur. The diagnosis is radio-clinical. The aim of this study is to demonstrate the effectiveness of surgical removal of the tumor, the therapeutic difficulty in certain osteoarticular localizations and finally the radio-clinical evolution after surgery. Material & methods We report the radio-clinical outcomes of a series of 15 children (4 girls/11 boys; aged of 03–14 years) with OO operated in our department, over a period of 08 years (2011–2019). Results The OO is located in most of cases of the lower limbs: acetabulum (1 case); femoral neck (3 cases); femoral diaphysis (2 cases); tibial diaphysis (4 cases); distal metaphysis of the tibia (1 case); talus (1 case) and in the spine (3 cases: vertebral body of T3, the posterior arch of T12 and the sacrum S3). Nocturnal pain yielding to aspirin, was the main symptom. It was associated with lameness when walking in patients with location of OO in the lower limbs. Diagnosis was delayed in patients with localization of OO in the spine (after 3 years) and in the talus (after 2 years). Imaging (standard Rx, CT scan and MRI) allowed the diagnosis of OO in all cases (nidus and cocarde image) and assessed the loco-regional impact (compression of the spinal canal in the sacral location; eccentricity of the femoral epiphysis, in the acetabular location, scoliosis in the spinal location). Thirteen children received surgical treatment under fluoroscopic guidance, which consisted of: A surgical abstention was decided in 2 cases: an inaccessible location at the bottom of the acetabulum and the T3 thoracic vertebral body localization in a 6-year-old girl. 12 operated children have good outcomes. However, 03 children experienced post-therapy problems: lumbar pain radiating towards the left thigh in the girl with sacral location (S3) despite the large laminectomy; a relapse 7 months later in the child with the femoral neck localization; A valgus misalignment of the right knee after removal of the OO of the proximal metaphysis of the tibia with a relapse 3 months later. Conclusion OO is a rare, benign tumor. However, certain locations can lead to diagnostic difficulties, loco-regional, organic and functional repercussions and certain constraints on their therapeutic management. Modern imaging helps to improve the care of these patients, both in terms of early diagnosis (scintigraphy, CT scan and MRI) and therapeutic precision (photo-coagulation, radiofrequency ablation).

Analysis of Fractal and Energy Consumption Characteristics of Concrete under Impact Loading

In order to study the compressive deformation and energy evolution characteristics of concrete under dynamic loading, impact compression tests with impact velocities of 5, 6, and 7 m/s were carried out on concrete samples with aggregate volume ratios of 0, 32%, 37%, and 42%, respectively, using a split Hopkinson pressure bar test apparatus. The broken concrete pieces after destruction were collected and arranged. The fractal characteristics of fragmentation distribution of concrete specimens with different aggregate rates under impact were discussed, and the roughness of the fragment surface was characterized by the fractal dimension of the broken fragment and the crack surface energy was calculated. In addition, the analytical equation of the fractal dimension of the broken fragment and the crack surface energy was established. The relationship between the specimen energy absorption and the crack surface energy was compared and analyzed. The results show that the concrete specimens are mainly tensile split failure modes under different impact speeds. The fractal dimension, absorption energy, and crack surface energy all increase with the increase in impact speed and decrease with the increase in the aggregate rate. When the aggregate rate is different, the effective utilization rate of the absorbed energy is the largest when the aggregate content is 37%. The surface energy of the crack can be used to estimate the concrete dynamic intensity.

Research On Water-Immersion Softening Mechanism of Coal Rock Mass Based on Split Hopkinson Pressure Bar Experiment

The coal mining process is affected by multiple sources of water such as groundwater and coal seam water injection. Understanding the dynamic mechanical parameters of water-immersed coal is helpful to the safe production of coal mines. The impact compression tests were performed on coal with different moisture contents by using the ϕ50 mm Split Hopkinson Pressure Bar (SHPB) experimental system, and the dynamic characteristics and energy loss laws of water-immersed coal with different compositions and water contents were analyzed. Through analysis and discussion, it is found that: (1) When the moisture content of the coal sample is 0%, 30%, 60%, the stress, strain rate and energy first increase and then decrease with time; (2) When the moisture content of the coal sample increases from 30% to 60%, the stress "plateau" of the coal sample disappears, resulting in an increase in the interval of the compressive stress and a decrease in the interval of the expansion stress. (3) The increase of the moisture content of the coal sample will affect its impact deformation and failure mode. When the moisture content is 60%, the incident rod end and the transmission rod end of the coal sample will have obvious compression failure, and the middle part of the coal sample will also experience expansion and deformation. (4) The coal composition ratio suitable for the impact experiment of coal immersion softening is optimized.

Face Damage Growth of Sandwich Composites under Compressive Loading: Experiments, Analytical and Finite Element Modeling

Sandwich panels with composite laminate skins having [(±45C)2,(0C,0G)4,(±45C)2] stacking sequence (subscript C for carbon fibers, G for glass) and containing barely visible impact damage (BVID) induced on the whole sandwich structure impacted at low energy, were tested in edge after-impact-compression with load direction parallel and transversal to the fibers direction (0-dir.). The morphology of impact damage on the sandwich structure was determined by using ultrasonic C-Scan and visual observation of laminate cross section. A Digital Image Correlation (DIC) system was used to measure the delamination evolution during the test. Two different failure behaviors were observed in two different impacted panels. Panel with fibers oriented transversally to the compressive load showed an opening (Mode-I) propagation of a delamination, while the panel with fibers parallel to the load showed shear (Mode-II) propagation. The static load such to determine local buckling of the composite face and failure was experimentally measured. An analytical model was implemented to predict the static strength of laminate with Mode-I opening. An FE model was instead built to predict the local buckling failure mode of the laminate with BVID, which is the first phenomenon to appear. The results of the analytical model and the numerical simulation correlate well with the test.

A Novel Design Method for Energy Absorption Property of Chiral Mechanical Metamaterials

In this paper, a full-cycle interactive progressive (FIP) method that integrates topology optimization, parametric optimization, and experimental analysis to determine the optimal energy absorption properties in the design of chiral mechanical metamaterials is proposed. The FIP method has improved ability and efficiency compared with traditional design methods due to strengthening the overall design, introducing surrogate models, and its consideration of the application conditions. Here, the FIP design was applied in the design of mechanical metamaterials with optimized energy absorption properties, and a chiral mechanical metamaterial with good energy absorption and impact resistance was obtained based on the rotation mechanism of metamaterials with a negative Poisson’s ratio. The relationship among the size parameters, applied boundary conditions, and energy absorption properties were studied. An impact compression experiment using a self-made Fiber Bragg Grating sensor was carried out on the chiral mechanical metamaterial. In light of the large deviation of the experimental and simulation data, a feedback adjustment was carried out by adjusting the structural parameters to further improve the mechanical properties of the chiral mechanical metamaterial. Finally, human–computer interaction, self-innovation, and a breakthrough in the design limits of the optimized model were achieved. The results illustrate the effectiveness of the FIP design method in improving the energy absorption properties in the design of chiral mechanical metamaterials.

Design, Manufacturing, and Characterization of Hybrid Carbon/Hemp Sandwich Panels

Advanced sandwich composite structures that incorporate foams or honeycombs as core materials, have been extensively investigated and used in various applications. One of the major limitations of the conventional materials used is their weak impact resistance and their end-of-life recyclability and overall sustainability. This paper is focused on the study of the production and mechanical characterization of hybrid sandwich panels using hemp bi-grid cores that were manufactured with an ad hoc continuous manufacturing process. Bi-grid structures were stratified in multiple layers, resulting in cores with different thicknesses and planar density. Sandwich panels made with carbon fibers skins were then subjected to Low Velocity Impact, compression and indentation and the damaged panels were investigated via CT-Scan. Results show that the high tailorability of the failure modes and the very good energy absorption properties of the hybrid material open new exciting perspectives for the development of new sandwich structures that can extend the use of natural fibers into several industrial applications.

JUTE AND COTTON COMPOSITES REINFORCED UNSATURATED POLYESTER

In this study, the effect of adding two different types of reinforcing natural fibers (jute and cotton) singly and in combination as a hybrid to unsaturated polyester resin was investigated. At the first discontinuous random fibers used in (5)mm length are added separately with different weight fraction as (3, 4.5, 6, and 7.5 wt.%) for both types fibers, then these fibers were mixed at (3.75 wt.% jute, 3.75 wt.% cotton) in (5)mm long. and The mechanical tests (hardness, Impact, and compression), as well as moisture absorption, are performed. The results show an increase in these properties with increasing weight fraction of fibers (jute & cotton) and reach the maximum amount at the addition of weight fraction of (7.5 wt.%) of both fibers (jute and cotton) separately. All composite specimens reinforced with jute fibers showed the highest hardness, Impact, compression, and moisture absorption among the composite specimen reinforced by cotton fibers and higher than in combination as a hybrid it was (93.1, 28.81 KJ/m2, 205 Mpa., and 1.4%) respectively.

Experimental Study on Physical and Dynamic Mechanical Properties of Temperature-Water Coupled Sandstone

In order to study the influence characteristics of water bath at different temperatures on rock physical and dynamic mechanical properties, a total of 15 groups of temperature-water bath treatment were carried out on coal mine roadway sandstone at 25°C∼95°C, and the basic physical parameters were tested. The impact compression test was carried out using the split Hopkinson pressure bar (SHPB) device. The results show that, with the increase of water bath temperature, the particle gap on the specimen surface increases. The volume, mass, and density of the specimens all increased with the increase of water bath temperature, and the increase was closely related to the water bath temperature. The dynamic compressive strength increases as a quadratic function of the water bath temperature, and the rate of increase is different before and after 45°C. The dynamic peak strain and average strain rate showed a quadratic function with the water bath temperature. The dynamic peak strain before 45°C decreased with the temperature increasing, and the dynamic peak strain after 45°C increased with the temperature increasing. The dynamic elastic modulus increased first and then decreased with the increase of water bath temperature and reached the maximum at 45°C. The failure pattern of sandstone is spalling. With the increase of water bath temperature, the fracture degree of the specimen gradually decreases.