Residual Strength Of Material Research Articles

Fire behavior of hemp blocks: A biomass-based construction material

Hemp blocks, also known as hempcrete, are eco-friendly and sustainable construction materials composed of hemp, lime, and water. In this study, the fire behaviour and structural performance of hemp-based materials were experimentally investigated. Fire exposure scenarios using raw hemp shives, hemp blocks, and non-load-bearing hemp block walls were examined. Tests conducted include cone calorimeter, bomb calorimeter, standard furnace, heat-transfer rating inducing system (H-TRIS), and small-scale elevated temperature material tests. Hemp shives exhibit ignition with sustained flaming, a relatively high heat release rate (HRR), and a relatively low critical heat flux (CHF). However, the hemp blocks exhibited no flaming ignition, only smouldering combustion, and an HRR an order of magnitude lower. Hemp blocks and hemp shives produced minimal smoke. Hemp blocks charred, and associated discoloration zones have been documented. Tests indicate that limited structural capacity is lost up until 200 °C, whereas at 300 °C, the residual material strength is almost negligible. The hemp block walls maintained their structural stability and integrity for 2 h of standard fire testing. The ambient-temperature compressive strength of the hemp blocks was determined to be 1.0 MPa. This work is the first comprehensive study on the fire behaviour of hemp blocks and highlights their good performance, whereby they are likely to have a limited impact on fire risk in buildings. Plastered walls will have a fire performance exceeding those reported here.

Condition assessment of timber beam in a typical Tibetan heritage building under crowd load

Many Tibetan heritage buildings in China are opened to tourists recently. The crowd load has become a significantly concern to the structural safety of the structures. The beams of these wooden structures are easily deformed or cracked under the crowd load. The condition assessment of the timber beam in a Tibetan heritage building under crowd load has become a new challenge. Convention statistical evaluation method making use of monitored strain data require a threshold value which is determined with no physical meaning. This paper separates the monitored strain into temperature-induced strain and crowd-induced strain. An analytical model of the timber beam including the semi-rigid connections at its ends is formulated for the calculation of different material stresses under crowd load. The condition of the beam is then quantitatively evaluated against the residual strength of material. The shear stress at any point of the beam can then be calculated from limited number of sensors for evaluating the more popular shear crack damage which is not monitored in most existing ancient structures.

Probability Model of Residual Strength of Materials Under Uncertain Cyclic Load

Residual strength is usually used to characterize the degradation rule of material performance under the cyclic load, which is critical to fatigue life prediction as well as reliability assessment of materials. In order to reveal the probability characteristics of residual strength of material under uncertain cyclic load, the relationship between external stress and fatigue life (i.e., the equation of S-N curve) is considered in this study. Firstly, the probability density function of fatigue life under uncertain cyclic load is derived from the probability density function of external stress. Then, a probability model of residual strength is proposed on the basis of a fundamental assumption that the residual strength and the remaining life of material depend on the same damage state. Finally, the validity of the proposed model is verified by an illustrative example. The results indicate that the probability distribution of residual strength of material is affected by both the external factor (i.e., probability characteristics of the load) and the internal factor (i.e., fatigue performance parameters of material).

АНАЛИЗ ТЕХНИЧЕСКОГО СОСТОЯНИЯ ЭКСПЛУАТИРУЕМЫХ ЖЕЛЕЗОБЕТОННЫХ КОНСТРУКЦИЙ С ИСПОЛЬЗОВАНИЕМ НЕЧЕТКОЙ ЛОГИКИ НА ОСНОВЕ ЭКСПЕРТНОЙ СИСТЕМЫ ОЦЕНКИ

Fuzzy logic is a useful tool when assessing the existing reinforced concrete structures. The introduction of expert system in assessing the technical condition of the existing structures built on the fuzzy logic represents a transition to a new and higher-quality level for the survey of constructions sites. The paper presents the principle of development and implementation of expert system for assessment of the damages of the existing structures. The process is based on the algorithm in which the input data (crack width and propagation, residual strength of materials, amount and condition of the steel reinforcement, deflection, corrosion level et al.) and information collected at each phase are processed and interpreted in order to define the successive step of the procedure. As a result, it is seen that the assessment of the existing building with precast concrete elements with usage of the proposed fuzzy system is in compliance with the estimation of the qualified experts.

Numerical modeling of high velocity impact applied to reinforced concrete panel

A numerical simulation of a high-velocity impact of reinforced concrete structures is a complex problem for which robust numerical models are required to predict the behavior of the experimental tests. This paper presents the implementation of a numerical model to predict the impact behavior of a reinforced concrete panel penetrated by a rigid ogive-nosed steel projectile. The concrete panel has dimensions of 675 mm × 675 mm × 200 mm, and is meshed using 8-node hexahedron solid elements. The behavior of the concrete panel is modeled using a Johnson-Holmquist damage model incorporating both the damage and residual material strength. The steel projectile has a small mass and a length of 152 mm, and is modeled as a rigid element. Damage and pressure contours are applied, and the kinetic and internal energies of the concrete and projectile are evaluated. We also evaluate the velocity at different points of the steel projectile and the concrete panel under an impact velocity of 540 m/s.

Biomechanical Study on the Influence of Shaping Amplitude on Material Strenght of Titanium Implant

The effect of shaping amplitude on the residual material strength of titanium implants was studied. A purposely built to and fro three point bending apparatus was developed for different amplitudes on the implant material. The strength of the material after different levels of amplitude was investigated thorough uniaxial tensile testing. The effect of stress concentration due to amplitude was investigated by finite element analysis. It was concluded that plastic deformation due to shaping amplitude produced different effect on the residual strength of the material.

Damage Progression and Residual Strength Evaluation in Sandwich Panels Loaded at the Center

This paper addresses damage evaluation of loaded sandwich panels by using acoustic emission (AE) as a non-destructive method. The specimens were loaded monotonically out-of-plane in control of displacement and the tests were stopped at three different damage levels. Each loading level activates different failure mechanism that can influence on residual strength of material. After each quasi-static test, the damaged plate was cut by a diamond saw to obtain tensile specimens. After cutting, compression test carried out by using acoustic emission to monitor the process. Depend on loading level the damage value was variant as it caused different residual strength that was related to acoustic emission signals activities. There is a relation between AE signal energy and mechanical energy that can follow to evaluate the residual strength of panels in different loading level in sandwich panels. Results show that the using AE method having mechanical results can be effective in residual strength and progressive damage evolution.

Books and literature

Papers read at the symposium on damage tolerance in aircraft structures, in Toronto in 1970 are here collected between hard covers. Altogether they review the state of aircraft structural analysis for structures with propagating cracks and present recent advancements in research into basic mechanisms of crack propagation and residual strength of aircraft structures. The papers also provide a review of fracture mechanics as applied to the assessment of structural vulnerability and residual strength of materials and structures. To achieve this, the papers fall into the categories of basic concepts in fatigue crack propagation, effects of panel geometry, influence of panel stiffeners and application of fracture mechanics and crack propagation to the design and test of aircraft structures.