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  1. LEGOs are one of the most popular toys and are known to be useful as instructional tools in STEM education. In this work, we used LEGO structures to demonstrate the energetic size effect on structural strength. Many material's fexural strength decreases with increasing structural size. We seek to demonstrate this effect in LEGO beams. Fracture experiments were performed using 3-point bend beams built of 2 X 4 LEGO blocks in a periodic staggered arrangement. LEGO wheels were used as rollers on either ends of the specimens which were weight compensated by adding counterweights. [1] Specimens were loaded by hanging weightsmore »at their midspan and the maximum sustained load was recorded. Specimens with a built-in defect (crack) of half specimen height were considered. Beam height was varied from two to 32 LEGO blocks while keeping the in-plane aspect ratio constant. The specimen thickness was kept constant at one LEGO block. Slow-motion videos and sound recordings of fractures were captured to determine how the fracture originated and propagated through the specimen. Flexural stress was calculated based on nominal specimen dimensions and fracture toughness was calculated following ASTM E-399 standard expressions from Srawley (1976). [2] The results demonstrate that the LEGO beams indeed exhibit a size effect on strength. For smaller beams the Uexural strength is higher than for larger beams. The dependence of strength on size is similar to that of Bažant’s size effect law [3] . Initiation of failure occurs consistently at the built-in defect. The staggered arrangement causes persistent crack branching which is more pronounced in larger specimens. The results also show that the apparent fracture toughness increases as the specimen size decreases. Further ongoing investigations consider the effects of the initial crack length on the size effect and the fracture response. The present work demonstrates that LEGO structures can serve as an instructional tool. We demonstrate principles of non-linear elastic fracture mechanics and highlight the importance of material microstructure (architecture) in fracture response. The experimental method is reproducible in a classroom setting without the need for complex facilities. This work was partially supported by the National Science Foundation (NSF) under the award #1662177 and the School of Mechanical Engineering at Purdue University. The authors acknowledge the support of Dr. Thomas Siegmund and Glynn Gallaway. [1] Khalilpour, S., BaniAsad, E. and Dehestani, M., 2019. A review on concrete fracture energy and effective parameters. Cement and Concrete research, 120, pp.294-321. [2] Srawley, J.E., 1976, January. Wide range stress intensity factor expressions for ASTM E 399 standard fracture toughness specimens. In Conf. of Am. Soc. for Testing and Mater., Committee E-24 (No. E-8654). [3] Bažant, Z.P., 1999. Size effect on structural strength: a review. Archive of applied Mechanics, 69(9), pp.703-725.« less
    Free, publicly-accessible full text available November 1, 2022
  2. Context. Brown dwarfs are transition objects between stars and planets that are still poorly understood, for which several competing mechanisms have been proposed to describe their formation. Mass measurements are generally difficult to carry out for isolated objects as well as for brown dwarfs orbiting low-mass stars, which are often too faint for a spectroscopic follow-up. Aims. Microlensing provides an alternative tool for the discovery and investigation of such faint systems. Here, we present an analysis of the microlensing event OGLE-2019-BLG-0033/MOA-2019-BLG-035, which is caused by a binary system composed of a brown dwarf orbiting a red dwarf. Methods. Thanks tomore »extensive ground observations and the availability of space observations from Spitzer, it has been possible to obtain accurate estimates of all microlensing parameters, including the parallax, source radius, and orbital motion of the binary lens. Results. Following an accurate modeling process, we found that the lens is composed of a red dwarf with a mass of M 1 = 0.149 ± 0.010 M ⊙ and a brown dwarf with a mass of M 2 = 0.0463 ± 0.0031 M ⊙ at a projected separation of a ⊥ = 0.585 au. The system has a peculiar velocity that is typical of old metal-poor populations in the thick disk. A percent-level precision in the mass measurement of brown dwarfs has been achieved only in a few microlensing events up to now, but will likely become more common in the future thanks to the Roman space telescope.« less
    Free, publicly-accessible full text available July 1, 2023
  3. Despite nationwide mandates to integrate computer science into P-6 curriculum, most P-6 preservice teachers (PSTs) are not exposed to coding or computational thinking during their professional preparation, and are unprepared to teach these topics. This study, conducted as a part of an NSF-funded project, explores a teacher preparation model designed to increase PSTs’ coding knowledge and coding self-efficacy. PSTs in an educational technology course partnered with engineering undergraduates (EUs) in a computational methods course and worked side-by-side on robotics activities to develop skill and confidence with basic programming concepts and block coding. Students utilized experience gained from these interdisciplinary partnershipsmore »to lead robotics activities with fifth and sixth grade students (FSGs) in an after-school technology club. Findings from quantitative studies suggest that the implementation of the approach resulted in a significant increase in both PSTs’ coding knowledge and coding self-efficacy. Qualitative studies revealed that most PSTs’ and EUs’ perceived value of the project was positive.« less
  4. This research paper presents preliminary results of an NSF-supported interdisciplinary collaboration between undergraduate engineering students and preservice teachers. The fields of engineering and elementary education share similar challenges when it comes to preparing undergraduate students for the new demands they will encounter in their profession. Engineering students need interprofessional skills that will help them value and negotiate the contributions of various disciplines while working on problems that require a multidisciplinary approach. Increasingly, the solutions to today's complex problems must integrate knowledge and practices from multiple disciplines and engineers must be able to recognize when expertise from outside their field canmore »enhance their perspective and ability to develop innovative solutions. However, research suggests that it is challenging even for professional engineers to understand the roles, responsibilities, and integration of various disciplines, and engineering curricula have traditionally left little room for development of non-technical skills such as effective communication with a range of audiences and an ability to collaborate in multidisciplinary teams. Meanwhile, preservice teachers need new technical knowledge and skills that go beyond traditional core content knowledge, as they are now expected to embed engineering into science and coding concepts into traditional subject areas. There are nationwide calls to integrate engineering and coding into PreK-6 education as part of a larger campaign to attract more students to STEM disciplines and to increase exposure for girls and minority students who remain significantly underrepresented in engineering and computer science. Accordingly, schools need teachers who have not only the knowledge and skills to integrate these topics into mainstream subjects, but also the intention to do so. However, research suggests that preservice teachers do not feel academically prepared and confident enough to teach engineering-related topics. This interdisciplinary project provided engineering students with an opportunity to develop interprofessional skills as well as to reinforce their technical knowledge, while preservice teachers had the opportunity to be exposed to engineering content, more specifically coding, and develop competence for their future teaching careers. Undergraduate engineering students enrolled in a computational methods course and preservice teachers enrolled in an educational technology course partnered to plan and deliver robotics lessons to fifth and sixth graders. This paper reports on the effects of this collaboration on twenty engineering students and eight preservice teachers. T-tests were used to compare participants’ pre-/post- scores on a coding quiz. A post-lesson written reflection asked the undergraduate students to describe their robotics lessons and what they learned from interacting with their cross disciplinary peers and the fifth/sixth graders. Content analysis was used to identify emergent themes. Engineering students’ perceptions were generally positive, recounting enjoyment interacting with elementary students and gaining communication skills from collaborating with non-technical partners. Preservice teachers demonstrated gains in their technical knowledge as measured by the coding quiz, but reported lacking the confidence to teach coding and robotics independently of their partner engineering students. Both groups reported gaining new perspectives from working in interdisciplinary teams and seeing benefits for the fifth and sixth grade participants, including exposing girls and students of color to engineering and computing.« less