Inverse Analyses in Fracture Mechanics

The present purpose is a survey of some engineering-oriented research results which may be representative of the main issues in the title subject. Some recent or current developments are pointed out in the growing area of fracture mechanics centered on the calibration of cohesive fracture models for quasi-brittle materials, by approaches which combine experimentation, experiment simulation and minimisation of the discrepancy between measured and computed quantities. Specifically, reference is made herein to the following topics in calibration of fracture constitutive models: (a) deterministic characterisation of concrete-like materials by traditional three-point-bending tests (TPBTs), supplemented by optical measurements; (b) wedge-splitting tests (WST) and extended Kalman filter (EKF) for the stochastic estimation of fracture parameters; (c) in situ parameter identification for the local diagnosis of possibly deteriorated concrete dams on the basis of flat-jack tests; (d) fracture properties of ceramic materials and coating-substrate interfaces identified through indentation tests, imprint mapping and inverse analysis in micro-technologies.     

Stochastic and recursive estimation of the hygro-thermo-chemical-mechanical parameters of concrete through Monte Carlo analysis and extended Kalman filter

Structural and Multidisciplinary Optimization - Hygro-thermo-chemical-mechanical models, used to determine the variations over time of temperature, relative humidity and shrinkage induced...     

Prediction of debonding strength of tensile steel/CFRP joints using fracture mechanics and stress based criteria

In this paper, the debonding strength of axially loaded double shear lap specimens between steel plates and carbon fibre reinforced plastic plates is investigated from the analytical, numerical and experimental point of view. Two steel plates were joined together by two carbon fibre reinforced plastic (CFRP) plates and epoxy adhesive in order to realize double shear lap specimens of different length. Failure of the steel-adhesive interface was identified as the dominant failure mode and fracture mechanics and stress based approach are presented in order to estimate the relevant failure load. A good agreement between the analytical-numerical results and experimental data is achieved.     

CFRP加固静定钢梁的弹-塑性响应

为对碳纤维增强复合材料加固的静定钢梁响应进行评估,提出一种简化方法。所提出的公式适用两种情况,一种是集中荷载作用下的简支梁;另一种是分布荷载作用下的简支梁。通过与试验数据的对比,验证了所提方法的有效性。     

Indentation and imprint mapping for the identification of interface properties in film-substrate systems

Indentation tests are frequently employed at present for the identification of material parameters at different scales. An innovative inverse analysis technique, recently proposed by the Authors, combines the traditional indentation test with the mapping of the residual deformations (imprint), thus providing experimental data apt to be used to identify material parameters in film-substrate systems. In this paper, such methodology is enhanced to permit the identification of the fracture properties of the interface between a coating and its substrate once the bulk material parameters are known. In order to make the inverse problem well posed, a further set of experimental data, namely the horizontal displacement field measured on the film external surface, is considered as available experimental information. The sought material parameters are recovered through recursive calculations of the mechanical response of the film-substrate system, performed by a finite strain numerical simulation. The coating and a significant portion of the underlying bulk material are incorporated in the finite element models built up to this purpose, while delamination is accounted for through cohesive elements. The inverse analysis procedure rests on a batch, deterministic approach and conventional optimization algorithms are employed for the minimization of a suitably defined discrepancy norm. Extensive numerical computations have been performed in order to test the performance of the proposed methodology in terms of result accuracy and computational effort.     

Indentation and imprint mapping for the identification of material properties in multi-layered systems

Multi-layered thin films have become popular thanks to their ability to enhance the performance, stiffness and strength of a component. In order to verify that the above properties are achieved in a production process, it is necessary to have reliable techniques to measure the mechanical parameters of such systems. Indentation tests are frequently employed for the identification of material parameters at different scales. In this context, this paper presents an inverse analysis technique which combines the indentation curve with the imprint geometry for the identification of the mechanical parameters of two alternating elasto-plastic hardening materials placed through the thickness of multi-layered systems. Three indentation-based inverse analysis methodologies are proposed for the identification of the sought material properties. Inverse analysis procedure consists of a batch, deterministic approach, and conventional optimization algorithms are employed for the minimization of the discrepancy norm. Extensive numerical computations have been performed in order to test the performance of the proposed methodologies in terms of result accuracy and computational effort.     

CFRP加固受拉钢构件的疲劳性能

对采用CFRP加固的钢结构的疲劳性能进行研究,完成了不同荷载条件下的初步试验以评估双侧加固试件的疲劳性能。由于粘合剂的连续剥离导致加固构件的刚度退化,因此,刚度退化被选择作为整体破坏的指标。观察发现,首先从板端部产生剥离,然后沿界面剥离直至破坏。对破坏后的粘合层检查发现,粘合剂-金属界面是加固系统的薄弱点。详细定义了S-N曲线,对试件的疲劳性能与欧洲规范3中详细分类的焊逢疲劳抗力进行比较,结果显示:钢板和碳纤维之间的粘合层疲劳抗力明显高于盖板焊缝的抗力(欧洲规范3:36*-56*条目)。     

Response of statically determined steel beams reinforced by CFRP plates in the elastic–plastic regime

The paper presents a simple approach to evaluate the response of statically determined steel beams reinforced by carbon fiber reinforced polymer (CFRP) plates in the elastic–plastic regime. The formulation is applied to two cases: simply supported beams both with distributed and concentrated load. The proposed solution is validated by comparison with experimental data available in the literature.