Experimental Study on the Novel Interface Bond Behavior between Fiber-Reinforced Concrete and Common Concrete through 3D-DIC

A novel method was proposed to improve the bond behavior of new-to-old concrete interface, which was beneficial to introduce the fiber-reinforced concrete only at the old concrete interface. This study investigated the effect of the fiber addition, strength grade of new concrete, interfacial angle, and surface treatment types on the bond behavior in terms of the new-to-old concrete through the axial tensile tests. The three-dimensional digital image correlation technique (3D-DIC) and scanning electron microscope were adopted to evaluate the variation of specimen surface strain distributions and microstructure of fiber-reinforced concrete and bond interface between new-to-old concrete. The experimental results indicated that interfacial angle and surface treatment type were significantly promoted bond behaviors, while the specimen cooperating with steel fibers had the highest bond strength. Besides, the maximum strain locations obtained from 3D-DIC method were the same as the location of the specimen failure, which indicated the 3D-DIC method can be adopted to forecast the structural failure. The microcrack strain located in the major crack was decreased with the development of the major crack. Ample crystals and Ca(OH)2 were generated in the interface between the new-to-old concrete to weaken the bond strength. Moreover, this paper provided the mechanics-driven and machine learning method to predict the bond strength. This study provides a new interface bonding method for the fabricated and large span structure to effectively avoid cracking of new-to-old concrete.

Effects of mortar compressive strength on out of plane response of unreinforced masonry walls

In this study, the out-of-plane response of infill walls that are widely used in Turkey and the surrounding regions were experimentally investigated. Several out-of-plane wall tests were performed in the laboratory, with the walls specimens produced with lateral hollow clay bricks (LHCB) and different mortar qualities. The walls were tested in their out-of-plane (OOP) direction under static load conditions and evaluated based on the load-bearing and energy dissipation capacities, crack propagations, mortar strengths, and initial stiffnesses. These walls are experimentally investigated to understand the effects of the mortar strength on the infill wall structural behaviors and to assess the effectiveness of the out-of-plane strength formulations. It was found that when the mortar strength is low, the first major crack occurs at the mortar, however, because of the arch mechanism efficiency in this situation the OOP load-carrying and energy dissipation capacities of unreinforced walls can be significantly increased. When the first major crack in the wall occurs in the brick itself, the arc mechanism is provided with delicate sections in the brick, which leads to strength decreasing in the walls. In this case, excessive deviations occur in the out-of-plane strength formulations estimates. This study shows that the arc mechanism, the damage start region and progress can change significantly unreinforced masonry (URM) infill walls behaviors.

Establishing Fracture Mechanics Based Minimum Allowable Temperatures for Low Temperature Applications of ASME B31.3 Piping

Impact test exemption curves in ASME B31.3 [1] were adopted from ASME Section VIII Division 1 (VIII-1) [2] with subtle modifications. The VIII-1 exemption curves were generated based on early fracture mechanics methodologies and limited amount of test data with an assumption on maximum applied stress intended to correspond to the typical VIII-1 allowable stress criteria. The applicability of the exemption curves for low temperature applications of ASME B31.3 piping (such as blowdown events) is open to discussion because of potentially high longitudinal thermal expansion stresses that may exceed the VIII-1 allowable stress criteria. Additionally, unlike in VIII-1 and ASME Section VIII Division 2 (VIII-2) [3], there is no post weld heat treatment (PWHT) credit on Minimum Design Metal Temperature (MDMT) in ASME B31.3. Detailed fracture mechanics analyses have shown that PWHT can significantly reduce the risk of brittle fracture failures due to its relaxation effect on weld residual stresses, a major crack driving force. In this paper, a fracture mechanics-based methodology for establishing Minimum Allowable Temperatures (MAT) for low temperature applications of ASME B31.3 piping is presented. A state-of-the-art fracture mechanics methodology published in Welding Research Council (WRC) Bulletin 562 [4] is used to develop step-by-step Level 1 and Level 2 procedures for establishing MAT for low temperature applications of ASME B31.3 piping. For the Level 1 methodology, MAT screening curves are developed based on a likely conservative assumption that the stresses in the piping component are at the maximum code allowable stresses in both the hoop and longitudinal directions. For the Level 2 methodology, stress ratio verses temperature reduction curves are developed to consider the effect of lower operating stresses. Similar to VIII-2 [3] toughness exemption curves, the screening curves are generated for both As-Welded and PWHT conditions. The curves can also be used for impact tested materials. The established MAT can be directly coupled to different reference flaw sizes and integrated with an inspection criteria for piping components. Two examples of establishing MAT using both the proposed Level 1 and Level 2 methodologies are presented herein.

Repair of Major Cracks in Central Spans of the 4 Span Continuous Bridge, India

Varsova Bridge is across Vasai Creek, about 35 Km from Mumbai, India. It is on National Highway 48. Two bridges, 555.32m long, exist at the crossing, built in 1970 and 2004 respectively. Old bridge has central 4 spans, built in continuous PSC box girder su configuration of 57.3 + 2 x 114.6 + 57.3 construction technique. 114.6m span on Mumbai end developed a major crack, 4mm wi about 12m from mid span. Main c height in both webs. The paper describes the investigations made through analysis the probable reasons and deciding remedial measures as well as execution of the same. used four different models as per construction material parameters. Final repair measure crack locations.

Virtual Testing for Advanced Aerospace Composites: Advances and Future Needs

In this paper, the conceptual, experimental, and computational challenges associated with virtual testing have been discussed and recent advances that address these challenges have been summarized. The promising capability of augmented finite element method based numerical platform for carry out structural level, subply scale, and microscopic single-fiber level analyses with explicit consideration of arbitrary cracking has been demonstrated through a hierarchical simulation-based analysis of a double-notched tension test reported in the literature. The simulation can account for the nonlinear coupling among all major damage modes relevant at different scales. Thus, it offers a complete picture of how microdamage processes interact with each other to eventually form a catastrophic major crack responsible for structural failure. In the exercise of virtual testing, such information is key to guide the design of discovery experiments to inform and calibrate models of the evolution processes. Urgent questions derived from this exercise are: How can we assure that damage models address all important mechanisms, how can we calibrate the material properties embedded in the models, and what constitutes sufficient validation of model predictions? The virtual test definition must include real tests that are designed in such a way as to be rich in the information needed to inform models and must also include model-based analyses of the tests that are required to acquire the information. Model-based analysis of tests must be undertaken and information-rich tests must be defined, taking proper account of the limitations of experimental methods and the stochastic nature of sublaminar and microscopic phenomena.

The Relationship between Shear Bands and Crack Growth Behavior in Ultrafine Grained Copper Processed by Severe Plastic Deformation

Fatigue life of smooth specimens is approximately controlled by the growth life of a small crack. This means the growth behavior of small cracks must be clarified to estimate the fatigue life of plain members. However, there are few studies on the growth behavior of small cracks in ultrafine grained (UFG) metals. In the present study, fatigue tests for UFG copper have been conducted. The formation behavior of shear bands (SBs) and growth behavior of a small crack have been monitored to clarify the effect of SBs on the growth behavior of a major crack.

Fatigue Failure Mechanism of CVT Rubber Belts

The fatigue failure mechanism was investigated for the rubber CVT (continuously variable transmission) belts. There are three major crack initiation modes in the rubber CVT belts, namely the adhesive rubber crack, the backing rubber crack and the bottomland crack. Especially, the mode of the adhesive rubber crack is important to strengthen the rubber CVT belts, because the crack is the most difficult to find out during the driving. In this study, the failure morphology of the damaged belts was observed using an optical microscope and a X-ray CT scan after some fatigue tests. Moreover, the failure mechanism of the adhesive rubber crack was discussed basing on the FEM and simplified mechanical analyses. The fatigue damage was accumulated along the interface between the cog rubber and the adhesive rubber. The interface was de-bonded by the shearing strain, which was induced by the dishing deformation of the belt within the pulley groove.