Cracks, microcracks and fracture in polymer structures: Formation, detection, autonomic repair

3D imaging has become popular for analyzing material microstructures. When time lapse series of 3D pictures are acquired during a single experiment, it is possible to measure displacement fields via digital volume correlation (DVC), thereby leading to 4D results. Such 4D analyses have been performed for almost two decades. The present paper aims at reviewing the achievements of and challenges faced by such measurement technique. Ex-situ and in-situ experiments are discussed. A general and unified DVC framework is introduced. Various sources of measurement bias and uncertainties are analyzed. The current challenges are studied and some propositions are given to address them.

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Digital Volume Correlation: Review of Progress and Challenges

Mixed mode fracture behavior of PMMA, was studied experimentally and theoretically using four different test configurations and with different crack types. Although all the test samples were subjected to three-point bend loading but completely different mixed mode fracture behaviors were observed for the tested samples. For each test configuration, especial mixed mode fracture toughness curves were obtained for fracture initiation direction and fracture toughness in the whole ranges of mixed mode I/II loading conditions. The level of crack tip constraint in the tested samples (which is related to the stress intensity factors ( K ) and the T -stress) was used as the main affecting parameter for predicting the mixed mode fracture results based on a two parameter ( K-T ) fracture theory. It was observed that the loss of crack tip constraint in the tested samples increases the mixed mode fracture resistance and decreases the fracture initiation direction and vice versa.

Mixed mode fracture toughness testing of PMMA with different three-point bend type specimens

Reclaimed asphalt pavement (RAP) is harder than virgin bitumen due to ageing and it needs to be rejuvenated. Three bio-based rejuvenators are used and the rejuvenating effects are evaluated. Rheological tests show how the rejuvenators may restore the mechanical properties of RAP binder. An ageing index is proposed to show that the rejuvenators are affected differently by ageing. Despite their addition, physio-chemical oxidation did not reverse. Mechanical changes were not caused by chemical changes at functional groups level but a rearrangement of polar/nonpolar components. The results show that considering the effect of aging is vital in identifying how rejuvenators affect the RAP binder chemically and mechanically.

Effect of ageing on the mechanical and chemical properties of binder from RAP treated with bio-based rejuvenators

Construction and demolition waste (CDW) accounts for at least 30% of the total solid waste produced around the world. At around 924 million tons in the European Union in 2016 and 2.36 billion tons in China in 2018, the amount is expected to increase over the next few years. Dumping these wastes in sanitary landfills has always been the traditional approach to waste management but this will not be feasible in the years to come. To significantly reduce or eliminate the amount of CDW being dumped, circular economy is a possible solution to the increasing amounts of CDW. Circular economy is an economic system based on business models which replaces the end-of-life concept with reducing, reusing, recycling, and recovering materials. This paper discusses circular economy (CE) frameworks-specifically material recovery and production highlighting the reuse and recycling of CDW and reprocessing into new construction applications. Likewise, a literature review into recent studies of reuse and recycling of CDW and its feasibility is also discussed to possibly prove the effectivity of CE in reducing CDW. Findings such as effectivity of recycling CDW into new construction applications and its limitations in effective usage are discussed and research gaps such as reuse of construction materials are also undertaken. CE and recycling were also found to be emerging topics. Observed trends in published articles as well as the use of latent Dirichlet allocation in creating topic models have shown a rising awareness and increasing research in CE which focuses on recycling and reusing CDW.

Circular Economy on Construction and Demolition Waste: A Literature Review on Material Recovery and Production

An experimental investigation of the scratch behaviour of polymers: 1. Influence of rate-dependent bulk mechanical properties

The experimental investigation herein described is aimed at understanding the effects of cellulose-based fibers on the mechanical properties of bituminous mastics for paving applications. Three bitumen (two of which modified with SBS polymers), a calcareous filler and four different types of fiber with varying content were used to prepare the investigated mastics. The filler to bitumen ratio was maintained constant. The laboratory investigations were focused on empirical tests (Needle Penetration and Ring and Ball – R&B – Temperature) and dynamic-mechanical tests, the latter performed in a wide range of temperatures. Results suggest that fibers improve the behavior of mastics for hot mix asphalts, particularly with respect to the prevention of rutting phenomena at high service temperatures.

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The effects of fibers on the performance of bituminous mastics for road pavements

An experimental investigation of the scratch behaviour of polymers – 2: Influence of hard or soft fillers

Use of recycled fillers in bituminous mixtures for road pavements

In many applications, polymeric foams (such as expanded polystyrene or expanded polypropylene) are used for protection from impacts. Standard design requires the foam to maximize the energy absorpt...

https://journals.sagepub.com/doi/pdf/10.1177/0021955X18806794

Luca Andena

Papers

An experimental investigation of the scratch behaviour of polymers: 1. Influence of rate-dependent bulk mechanical properties

The effects of fibers on the performance of bituminous mastics for road pavements

An experimental investigation of the scratch behaviour of polymers – 2: Influence of hard or soft fillers

Use of recycled fillers in bituminous mixtures for road pavements

Compression of polystyrene and polypropylene foams for energy absorption applications: A combined mechanical and microstructural study: